Astigmatism aberration as a function of distance

[Lu Yan]

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Hi folks,

I am building a fiber based confocal microscopy setup (with sample stage
scanning). But I always got some astigmatism aberration in PSF measuremnts.
The similar aberration was there even I replaced the objective lens with a
regular lens and imaged my illumination beam through that lens with a
camera. I got elongated beam 'spot' on both sides of the focal plane, and
the orientation of the two 'spot' were orthogonal. I think that is
astigmatism aberration if I am not mistaken. I draw a schematic in Evernote
so I can include it here. Here is the link:
https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
(copy and paste if the link does not work in email)

I tried to adjust both lens in xy to avoid off-axis incident, but the
aberration would go away. So I got confused where they came from. I hope
someone here could lead me a direction to further look into it.

Thanks very much,
Lu
-----------------------------------------------------
​​

Lu Yan
Nanostructured Fibers and Nonlinear Optics Laboratory
Electrical and Computer Engineering
Boston University
8 St. Mary St., Boston, MA, 02215
[phone]
-----------------------------------------------------

[Michael Giacomelli]

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Hi Lu,

In an on axis system like you have drawn there should be no astigmatism if
the fiber is well centered on the optic.  Assuming you've correctly aligned
the collimator, I would think it is some other aberration you are seeing.

Regarding your questions in that linked page:

1)  It depends on what you want to collect.  4f (or some other imaging
condition) will give you maximum light collection, which is likely what you
want if you have selected a multimode fiber.  Alternatively, if this is a
confocal system, it is probably not necessary.

2)  The diagram shows a collimated single mode fiber.  That should be
independent of distance.  If you find that your spot is changing rapidly
with distance, likely something is wrong with the collimation.  What are
you using a collimator?  Is it suitable for the NA and wavelength/bandwidth
of your source?  Is it well aligned?  What is the exact model of fiber you
are using.

3)  Most likely it is a problem with your coupler.

Mike

On Tue, Nov 4, 2014 at 11:36 PM, Yan, Lu <[hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> Hi folks,
>
> I am building a fiber based confocal microscopy setup (with sample stage
> scanning). But I always got some astigmatism aberration in PSF measuremnts.
> The similar aberration was there even I replaced the objective lens with a
> regular lens and imaged my illumination beam through that lens with a
> camera. I got elongated beam 'spot' on both sides of the focal plane, and
> the orientation of the two 'spot' were orthogonal. I think that is
> astigmatism aberration if I am not mistaken. I draw a schematic in Evernote
> so I can include it here. Here is the link:
>
> https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
> (copy and paste if the link does not work in email)
>
> I tried to adjust both lens in xy to avoid off-axis incident, but the
> aberration would go away. So I got confused where they came from. I hope
> someone here could lead me a direction to further look into it.
>
> Thanks very much,
> Lu
> -----------------------------------------------------
> ​​
>
> Lu Yan
> Nanostructured Fibers and Nonlinear Optics Laboratory
> Electrical and Computer Engineering
> Boston University
> 8 St. Mary St., Boston, MA, 02215
> [phone]
> -----------------------------------------------------
>

[Lu Yan]

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*****

Hi Mike,

Thanks for promote reply. Like you said for an on axis system (especially
simple as mine), astigmatism should not be there, and that why it confused
me a lot. I am currently using a Thorlabs air-spaced achromatic lens
(f=30mm) (http://www.thorlabs.com/thorproduct.cfm?partnumber=ACA254-030-A)
for the collimation. The fiber I have tried are SMF600 and RBG 400, both of
which are single mode at 632 nm. I usually looked at the back reflection
(from surfaces of the lens) formed interference pattern (concentric rings)
to align my fiber w.r.t. my fiber facet.

For your comments on my questions:

1) I am using the multimode fiber as the pinhole to achieve confocal.
2) Looking at the beam spot after the collimation lens, it was not changing
much even at several meters away from the lens. The spot changed rapidly
around the focal plane if the beam was reimaged through another lens (e.g.
L2 or L3 in the linked page). I think the NA is large enough for the fiber
I am using.
3) I was thinking maybe the fiber tip is tilted with respect to the
collimation lens plane? Would that cause problem? OR would that still give
me concentric rings pattern centered at my fiber tip (if the fiber is
tilted w.r.t. the lens plane)?

Thanks,
Lu

-----------------------------------------------------
Lu Yan
Nanostructured Fibers and Nonlinear Optics Laboratory
Electrical and Computer Engineering
Boston University
8 St. Mary St., Boston, MA, 02215
[phone]
[hidden email]
-----------------------------------------------------

On Wed, Nov 5, 2014 at 12:37 AM, Michael Giacomelli <[hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> Hi Lu,
>
> In an on axis system like you have drawn there should be no astigmatism if
> the fiber is well centered on the optic.  Assuming you've correctly aligned
> the collimator, I would think it is some other aberration you are seeing.
>
> Regarding your questions in that linked page:
>
> 1)  It depends on what you want to collect.  4f (or some other imaging
> condition) will give you maximum light collection, which is likely what you
> want if you have selected a multimode fiber.  Alternatively, if this is a
> confocal system, it is probably not necessary.
>
> 2)  The diagram shows a collimated single mode fiber.  That should be
> independent of distance.  If you find that your spot is changing rapidly
> with distance, likely something is wrong with the collimation.  What are
> you using a collimator?  Is it suitable for the NA and wavelength/bandwidth
> of your source?  Is it well aligned?  What is the exact model of fiber you
> are using.
>
> 3)  Most likely it is a problem with your coupler.
>
> Mike
>
> On Tue, Nov 4, 2014 at 11:36 PM, Yan, Lu <[hidden email]> wrote:
>
> > *****
> > To join, leave or search the confocal microscopy listserv, go to:
> > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > Post images on http://www.imgur.com and include the link in your
> posting.
> > *****
> >
> > Hi folks,
> >
> > I am building a fiber based confocal microscopy setup (with sample stage
> > scanning). But I always got some astigmatism aberration in PSF
> measuremnts.
> > The similar aberration was there even I replaced the objective lens with
> a
> > regular lens and imaged my illumination beam through that lens with a
> > camera. I got elongated beam 'spot' on both sides of the focal plane, and
> > the orientation of the two 'spot' were orthogonal. I think that is
> > astigmatism aberration if I am not mistaken. I draw a schematic in
> Evernote
> > so I can include it here. Here is the link:
> >
> >
> https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
> > (copy and paste if the link does not work in email)
> >
> > I tried to adjust both lens in xy to avoid off-axis incident, but the
> > aberration would go away. So I got confused where they came from. I hope
> > someone here could lead me a direction to further look into it.
> >
> > Thanks very much,
> > Lu
> > -----------------------------------------------------
> > ​​
> >
> > Lu Yan
> > Nanostructured Fibers and Nonlinear Optics Laboratory
> > Electrical and Computer Engineering
> > Boston University
> > 8 St. Mary St., Boston, MA, 02215
> > [phone]
> > -----------------------------------------------------
> >
>

[Kyle Michael Douglass]

*****
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http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
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*****

Hi Lu,

     On 11/05/2014 05:36 AM, Yan, Lu wrote:

> Hi folks,
>
> I am building a fiber based confocal microscopy setup (with sample stage
> scanning). But I always got some astigmatism aberration in PSF measuremnts.
> The similar aberration was there even I replaced the objective lens with a
> regular lens and imaged my illumination beam through that lens with a
> camera. I got elongated beam 'spot' on both sides of the focal plane, and
> the orientation of the two 'spot' were orthogonal. I think that is
> astigmatism aberration if I am not mistaken. I draw a schematic in Evernote
> so I can include it here. Here is the link:
> https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
> (copy and paste if the link does not work in email)
>
> I tried to adjust both lens in xy to avoid off-axis incident, but the
> aberration would go away. So I got confused where they came from. I hope
> someone here could lead me a direction to further look into it.
>
> Thanks very much,
> Lu

Here are two quick checks that came to mind. Maybe you've tried them,
but it's still good to check all the possible sources of the problem:

1) Is the beam splitter really a glass cube as it's drawn, or one of the
thin dichroic-like beam splitters? Sometimes the thin dichroics are
slightly warped in one direction and can introduce astigmatism after
reflection.

2) When you illuminate a flat surface or white piece of paper with light
directly coming from the single mode fiber, do you see a smooth,
homogeneous intensity distribution or some other kind of structure? I've
noticed that one can occasionally get a weak first-order mode coming
from the fiber if the wavelength is close to the multimode cut-on. It
may not necessarily lead to astigmatism, but it's still good to check.

Good luck!

Dr. Kyle Douglass
The Laboratory of Experimental Biophysics
EPFL, Lausanne, Switzerland

[Mark Cannell-2]

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*****

I agree, it could be the mirrors -are they pinched in some way or else you have a lens/source off axis.
HTH

Mark

On 5/11/2014, at 7:56 am, Kyle Douglass <[hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> Hi Lu,
>
>    On 11/05/2014 05:36 AM, Yan, Lu wrote:
>> Hi folks,
>>
>> I am building a fiber based confocal microscopy setup (with sample stage
>> scanning). But I always got some astigmatism aberration in PSF measuremnts.
>> The similar aberration was there even I replaced the objective lens with a
>> regular lens and imaged my illumination beam through that lens with a
>> camera. I got elongated beam 'spot' on both sides of the focal plane, and
>> the orientation of the two 'spot' were orthogonal. I think that is
>> astigmatism aberration if I am not mistaken. I draw a schematic in Evernote
>> so I can include it here. Here is the link:
>> https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
>> (copy and paste if the link does not work in email)
>>
>> I tried to adjust both lens in xy to avoid off-axis incident, but the
>> aberration would go away. So I got confused where they came from. I hope
>> someone here could lead me a direction to further look into it.
>>
>> Thanks very much,
>> Lu
> Here are two quick checks that came to mind. Maybe you've tried them, but it's still good to check all the possible sources of the problem:
>
> 1) Is the beam splitter really a glass cube as it's drawn, or one of the thin dichroic-like beam splitters? Sometimes the thin dichroics are slightly warped in one direction and can introduce astigmatism after reflection.
>
> 2) When you illuminate a flat surface or white piece of paper with light directly coming from the single mode fiber, do you see a smooth, homogeneous intensity distribution or some other kind of structure? I've noticed that one can occasionally get a weak first-order mode coming from the fiber if the wavelength is close to the multimode cut-on. It may not necessarily lead to astigmatism, but it's still good to check.
>
> Good luck!
>
> Dr. Kyle Douglass
> The Laboratory of Experimental Biophysics
> EPFL, Lausanne, Switzerland

Mark  B. Cannell Ph.D. FRSNZ
Professor of Cardiac Cell Biology
School of Physiology &  Pharmacology
Medical Sciences Building
University of Bristol
Bristol
BS8 1TD UK

[hidden email]

[Lu Yan]

*****
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*****

Hi Kyle, Mark,

Thanks for your suggestions. Regarding to Kyle's comments/questions:

1) my beam splitter is those cube beam splitter. I should have mentioned
that even without beam splitter, when I imaged the collimated beam through
a lens far away from the collimation lens [between two lenses are just two
mirrors (1 inch Thorlabs silver protected mirror)], I got similar amount of
astigmatism. [To Mark: would mirrors usually also cause astigmatism in
microscopy? Then does that make sense to use larger mirrors? my beam 1/e^2
size is about 5 mm in diameter.]

2) the fiber is single moded, and I have tried imaging is using a 150X
Nikon objective lens (single lens imaging), and it does not have higher
order mode, pretty Gaussian. BTW, imaging with 150X obj. did not give me
astigmatism as I moved the fiber (or the camera) back and forth.

Besides these, I have another question about astigmatism. Supposed that I
have an off-axis lens for the collimation of my Gaussian illumination beam,
does the amount of astigmatism I will get depend on the distance after
which I will image the Gaussian beam?

Thanks,
Lu

-----------------------------------------------------
Lu Yan
Nanostructured Fibers and Nonlinear Optics Laboratory
Electrical and Computer Engineering
Boston University
8 St. Mary St., Boston, MA, 02215
[phone]
[hidden email]
-----------------------------------------------------

On Wed, Nov 5, 2014 at 3:04 AM, Mark Cannell <[hidden email]>
wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> I agree, it could be the mirrors -are they pinched in some way or else you
> have a lens/source off axis.
> HTH
>
> Mark
>
> On 5/11/2014, at 7:56 am, Kyle Douglass <[hidden email]> wrote:
>
> > *****
> > To join, leave or search the confocal microscopy listserv, go to:
> > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > Post images on http://www.imgur.com and include the link in your
> posting.
> > *****
> >
> > Hi Lu,
> >
> >    On 11/05/2014 05:36 AM, Yan, Lu wrote:
> >> Hi folks,
> >>
> >> I am building a fiber based confocal microscopy setup (with sample stage
> >> scanning). But I always got some astigmatism aberration in PSF
> measuremnts.
> >> The similar aberration was there even I replaced the objective lens
> with a
> >> regular lens and imaged my illumination beam through that lens with a
> >> camera. I got elongated beam 'spot' on both sides of the focal plane,
> and
> >> the orientation of the two 'spot' were orthogonal. I think that is
> >> astigmatism aberration if I am not mistaken. I draw a schematic in
> Evernote
> >> so I can include it here. Here is the link:
> >>
> https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
> >> (copy and paste if the link does not work in email)
> >>
> >> I tried to adjust both lens in xy to avoid off-axis incident, but the
> >> aberration would go away. So I got confused where they came from. I hope
> >> someone here could lead me a direction to further look into it.
> >>
> >> Thanks very much,
> >> Lu
> > Here are two quick checks that came to mind. Maybe you've tried them,
> but it's still good to check all the possible sources of the problem:
> >
> > 1) Is the beam splitter really a glass cube as it's drawn, or one of the
> thin dichroic-like beam splitters? Sometimes the thin dichroics are
> slightly warped in one direction and can introduce astigmatism after
> reflection.
> >
> > 2) When you illuminate a flat surface or white piece of paper with light
> directly coming from the single mode fiber, do you see a smooth,
> homogeneous intensity distribution or some other kind of structure? I've
> noticed that one can occasionally get a weak first-order mode coming from
> the fiber if the wavelength is close to the multimode cut-on. It may not
> necessarily lead to astigmatism, but it's still good to check.
> >
> > Good luck!
> >
> > Dr. Kyle Douglass
> > The Laboratory of Experimental Biophysics
> > EPFL, Lausanne, Switzerland
>
> Mark  B. Cannell Ph.D. FRSNZ
> Professor of Cardiac Cell Biology
> School of Physiology &  Pharmacology
> Medical Sciences Building
> University of Bristol
> Bristol
> BS8 1TD UK
>
> [hidden email]
>

[Kyle Michael Douglass]

*****
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*****

Hi Lu and others,

On 11/05/2014 10:08 AM, Yan, Lu wrote:
> 1) my beam splitter is those cube beam splitter. I should have mentioned
> that even without beam splitter, when I imaged the collimated beam through
> a lens far away from the collimation lens [between two lenses are just two
> mirrors (1 inch Thorlabs silver protected mirror)], I got similar amount of
> astigmatism. [To Mark: would mirrors usually also cause astigmatism in
> microscopy? Then does that make sense to use larger mirrors? my beam 1/e^2
> size is about 5 mm in diameter.]
>

OK, if it's a cube then you probably don't have any warping of the
reflecting surface. And mirrors tend to be flatter than dichroics, so I
doubt they're warped (unless you've mounted them in a way to put a lot
of stress in one direction of the mirror).

Like Mike suggested earlier, I'm now thinking that it's likely a problem
with the collimator. Since it's an air-spaced achromat, I suppose it's
possible that the lens are misaligned relative to one another.

What happens if you try a singlet lens with the same focal length?

Kyle

[Mark Cannell-2]

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*****

Hi Lu

A mirror can produce astigmatism -if it is bent by pressure from the mount. The amount of astigmatism may not depend on distance -depends on where it is arising -for sure if you have to move an alignment tilt screw when moving an optic along the axis you have something off axis. Astigmatism is most easily produced by a surface that does not have equal radii of curvature in two orthogonal directions this could be a tilted spherical surface or a bent plane and you don’t need much to see the effect -just a one wave error in the wavefront will do…  That you lost the astigmatism when you substituted a 150x objective suggests to me that you look at the collimator. Have you considered looking at fringes to help you decide what the error is? Look at some of the telescope literature on the web to see how to do this.  

As a last thought, you don’t by any chance have a DIC wedge in the system do you and you are not seeing an eyepiece problem?

And a beam diameter of 5mm sounds a bit small to fill the rear aperture of most objectives...

HTH

Mark


a cylindrical lens -which is what you get of you go off axis
On 5/11/2014, at 9:08 am, Yan, Lu <[hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> Hi Kyle, Mark,
>
> Thanks for your suggestions. Regarding to Kyle's comments/questions:
>
> 1) my beam splitter is those cube beam splitter. I should have mentioned
> that even without beam splitter, when I imaged the collimated beam through
> a lens far away from the collimation lens [between two lenses are just two
> mirrors (1 inch Thorlabs silver protected mirror)], I got similar amount of
> astigmatism. [To Mark: would mirrors usually also cause astigmatism in
> microscopy? Then does that make sense to use larger mirrors? my beam 1/e^2
> size is about 5 mm in diameter.]
>
> 2) the fiber is single moded, and I have tried imaging is using a 150X
> Nikon objective lens (single lens imaging), and it does not have higher
> order mode, pretty Gaussian. BTW, imaging with 150X obj. did not give me
> astigmatism as I moved the fiber (or the camera) back and forth.
>
> Besides these, I have another question about astigmatism. Supposed that I
> have an off-axis lens for the collimation of my Gaussian illumination beam,
> does the amount of astigmatism I will get depend on the distance after
> which I will image the Gaussian beam?
>
> Thanks,
> Lu
>
> -----------------------------------------------------
> Lu Yan
> Nanostructured Fibers and Nonlinear Optics Laboratory
> Electrical and Computer Engineering
> Boston University
> 8 St. Mary St., Boston, MA, 02215
> [phone]
> [hidden email]
> -----------------------------------------------------
>
> On Wed, Nov 5, 2014 at 3:04 AM, Mark Cannell <[hidden email]>
> wrote:
>
>> *****
>> To join, leave or search the confocal microscopy listserv, go to:
>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>> Post images on http://www.imgur.com and include the link in your posting.
>> *****
>>
>> I agree, it could be the mirrors -are they pinched in some way or else you
>> have a lens/source off axis.
>> HTH
>>
>> Mark
>>
>> On 5/11/2014, at 7:56 am, Kyle Douglass <[hidden email]> wrote:
>>
>>> *****
>>> To join, leave or search the confocal microscopy listserv, go to:
>>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>>> Post images on http://www.imgur.com and include the link in your
>> posting.
>>> *****
>>>
>>> Hi Lu,
>>>
>>>   On 11/05/2014 05:36 AM, Yan, Lu wrote:
>>>> Hi folks,
>>>>
>>>> I am building a fiber based confocal microscopy setup (with sample stage
>>>> scanning). But I always got some astigmatism aberration in PSF
>> measuremnts.
>>>> The similar aberration was there even I replaced the objective lens
>> with a
>>>> regular lens and imaged my illumination beam through that lens with a
>>>> camera. I got elongated beam 'spot' on both sides of the focal plane,
>> and
>>>> the orientation of the two 'spot' were orthogonal. I think that is
>>>> astigmatism aberration if I am not mistaken. I draw a schematic in
>> Evernote
>>>> so I can include it here. Here is the link:
>>>>
>> https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
>>>> (copy and paste if the link does not work in email)
>>>>
>>>> I tried to adjust both lens in xy to avoid off-axis incident, but the
>>>> aberration would go away. So I got confused where they came from. I hope
>>>> someone here could lead me a direction to further look into it.
>>>>
>>>> Thanks very much,
>>>> Lu
>>> Here are two quick checks that came to mind. Maybe you've tried them,
>> but it's still good to check all the possible sources of the problem:
>>>
>>> 1) Is the beam splitter really a glass cube as it's drawn, or one of the
>> thin dichroic-like beam splitters? Sometimes the thin dichroics are
>> slightly warped in one direction and can introduce astigmatism after
>> reflection.
>>>
>>> 2) When you illuminate a flat surface or white piece of paper with light
>> directly coming from the single mode fiber, do you see a smooth,
>> homogeneous intensity distribution or some other kind of structure? I've
>> noticed that one can occasionally get a weak first-order mode coming from
>> the fiber if the wavelength is close to the multimode cut-on. It may not
>> necessarily lead to astigmatism, but it's still good to check.
>>>
>>> Good luck!
>>>
>>> Dr. Kyle Douglass
>>> The Laboratory of Experimental Biophysics
>>> EPFL, Lausanne, Switzerland
>>
>> Mark  B. Cannell Ph.D. FRSNZ
>> Professor of Cardiac Cell Biology
>> School of Physiology &  Pharmacology
>> Medical Sciences Building
>> University of Bristol
>> Bristol
>> BS8 1TD UK
>>
>> [hidden email]
>>

[Michael Giacomelli]

*****
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*****

Hi Lu,

Regarding your collimator, using short focal length achromats is usually a
bad idea unless you are using a very broadband laser (E.g. short pulse
ti:saph or supercontinuum).  Instead, aspheric couplers are usually used as
an achromat will have significant spherical aberration.  If you do use an
achromat, make sure that do not use it backwards (always minimize
glass-wavefront curvature - flatter face into diverging wavefront, curved
face into collimated wavefront) and if possible simulate in zemax to be
sure before trying it.  Just simulating the AC254-30-A, putting the lens in
backwards results in a massively abberated beam.  I would double check that
first.  Alternatively, buying an aspheric may be a better idea. Technically
the AC254-30-A is ok, but only just, only if perfectly aligned.  You have
little margin for error.

If you haven't already, I recommend aligning the coupler to the grid of
your table, and running the beam quite far out and ensuring that it is
truly parallel to that grid (and thus perpendicular to lens face).  Because
of the short focal length, you must be very precise here, with an error of
about a quarter of a millimeter in centration introducing noticeable
astigmatism.  I recommend a good 3 axis kinematic.

Regarding tilt of the fiber face, usually fibers are angle cleaved, and
then mounted in a coupler with a matching tilt.  Make sure that if you used
an APC fiber, you have an APC mount, and if you used a flat cleaved fiber,
you have an un-angled mount.

Regarding mirrors, a standard thorlabs mirror used in one of their mounts
will have negligible astigmatism when used with a beam of your diameter.
It is true that mirrors can and do introduce aberration into beams, but
with such a narrow beam diameter, even a relatively poor mirror will not
introduce noticeable phase error.  These problems are much more common at
2" and above.

By the way, do you have access to a beam profiler?  Taking an image of this
focal spot and posting it might give some clues.

Mike




On Wed, Nov 5, 2014 at 1:11 AM, Yan, Lu <[hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> Hi Mike,
>
> Thanks for promote reply. Like you said for an on axis system (especially
> simple as mine), astigmatism should not be there, and that why it confused
> me a lot. I am currently using a Thorlabs air-spaced achromatic lens
> (f=30mm) (http://www.thorlabs.com/thorproduct.cfm?partnumber=ACA254-030-A)
> for the collimation. The fiber I have tried are SMF600 and RBG 400, both of
> which are single mode at 632 nm. I usually looked at the back reflection
> (from surfaces of the lens) formed interference pattern (concentric rings)
> to align my fiber w.r.t. my fiber facet.
>
> For your comments on my questions:
>
> 1) I am using the multimode fiber as the pinhole to achieve confocal.
> 2) Looking at the beam spot after the collimation lens, it was not changing
> much even at several meters away from the lens. The spot changed rapidly
> around the focal plane if the beam was reimaged through another lens (e.g.
> L2 or L3 in the linked page). I think the NA is large enough for the fiber
> I am using.
> 3) I was thinking maybe the fiber tip is tilted with respect to the
> collimation lens plane? Would that cause problem? OR would that still give
> me concentric rings pattern centered at my fiber tip (if the fiber is
> tilted w.r.t. the lens plane)?
>
> Thanks,
> Lu
>
> -----------------------------------------------------
> Lu Yan
> Nanostructured Fibers and Nonlinear Optics Laboratory
> Electrical and Computer Engineering
> Boston University
> 8 St. Mary St., Boston, MA, 02215
> [phone]
> [hidden email]
> -----------------------------------------------------
>
> On Wed, Nov 5, 2014 at 12:37 AM, Michael Giacomelli <[hidden email]> wrote:
>
> > *****
> > To join, leave or search the confocal microscopy listserv, go to:
> > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > Post images on http://www.imgur.com and include the link in your
> posting.
> > *****
> >
> > Hi Lu,
> >
> > In an on axis system like you have drawn there should be no astigmatism
> if
> > the fiber is well centered on the optic.  Assuming you've correctly
> aligned
> > the collimator, I would think it is some other aberration you are seeing.
> >
> > Regarding your questions in that linked page:
> >
> > 1)  It depends on what you want to collect.  4f (or some other imaging
> > condition) will give you maximum light collection, which is likely what
> you
> > want if you have selected a multimode fiber.  Alternatively, if this is a
> > confocal system, it is probably not necessary.
> >
> > 2)  The diagram shows a collimated single mode fiber.  That should be
> > independent of distance.  If you find that your spot is changing rapidly
> > with distance, likely something is wrong with the collimation.  What are
> > you using a collimator?  Is it suitable for the NA and
> wavelength/bandwidth
> > of your source?  Is it well aligned?  What is the exact model of fiber
> you
> > are using.
> >
> > 3)  Most likely it is a problem with your coupler.
> >
> > Mike
> >
> > On Tue, Nov 4, 2014 at 11:36 PM, Yan, Lu <[hidden email]> wrote:
> >
> > > *****
> > > To join, leave or search the confocal microscopy listserv, go to:
> > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > Post images on http://www.imgur.com and include the link in your
> > posting.
> > > *****
> > >
> > > Hi folks,
> > >
> > > I am building a fiber based confocal microscopy setup (with sample
> stage
> > > scanning). But I always got some astigmatism aberration in PSF
> > measuremnts.
> > > The similar aberration was there even I replaced the objective lens
> with
> > a
> > > regular lens and imaged my illumination beam through that lens with a
> > > camera. I got elongated beam 'spot' on both sides of the focal plane,
> and
> > > the orientation of the two 'spot' were orthogonal. I think that is
> > > astigmatism aberration if I am not mistaken. I draw a schematic in
> > Evernote
> > > so I can include it here. Here is the link:
> > >
> > >
> >
> https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
> > > (copy and paste if the link does not work in email)
> > >
> > > I tried to adjust both lens in xy to avoid off-axis incident, but the
> > > aberration would go away. So I got confused where they came from. I
> hope
> > > someone here could lead me a direction to further look into it.
> > >
> > > Thanks very much,
> > > Lu
> > > -----------------------------------------------------
> > > ​​
> > >
> > > Lu Yan
> > > Nanostructured Fibers and Nonlinear Optics Laboratory
> > > Electrical and Computer Engineering
> > > Boston University
> > > 8 St. Mary St., Boston, MA, 02215
> > > [phone]
> > > -----------------------------------------------------
> > >
> >
>

[Lu Yan]

*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
Post images on http://www.imgur.com and include the link in your posting.
*****

Hi Mark,

I will check how tight I mounted the mirrors. For the fringes things, I
will look into it. And I don't have a DIC wedge in the system. Now I am
just trying to figure out why the astigmatism happened when I had such a
simple system, i.e. fiber+collimation lens+imaging lens+camera. I will
check on the collimator.

Thanks
Lu

-----------------------------------------------------
Lu Yan
Nanostructured Fibers and Nonlinear Optics Laboratory
Electrical and Computer Engineering
Boston University
8 St. Mary St., Boston, MA, 02215
[phone]
[hidden email]
-----------------------------------------------------

On Wed, Nov 5, 2014 at 5:21 AM, Mark Cannell <[hidden email]>
wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> Hi Lu
>
> A mirror can produce astigmatism -if it is bent by pressure from the
> mount. The amount of astigmatism may not depend on distance -depends on
> where it is arising -for sure if you have to move an alignment tilt screw
> when moving an optic along the axis you have something off axis.
> Astigmatism is most easily produced by a surface that does not have equal
> radii of curvature in two orthogonal directions this could be a tilted
> spherical surface or a bent plane and you don’t need much to see the effect
> -just a one wave error in the wavefront will do…  That you lost the
> astigmatism when you substituted a 150x objective suggests to me that you
> look at the collimator. Have you considered looking at fringes to help you
> decide what the error is? Look at some of the telescope literature on the
> web to see how to do this.
>
> As a last thought, you don’t by any chance have a DIC wedge in the system
> do you and you are not seeing an eyepiece problem?
>
> And a beam diameter of 5mm sounds a bit small to fill the rear aperture of
> most objectives...
>
> HTH
>
> Mark
>
>
> a cylindrical lens -which is what you get of you go off axis
> On 5/11/2014, at 9:08 am, Yan, Lu <[hidden email]> wrote:
>
> > *****
> > To join, leave or search the confocal microscopy listserv, go to:
> > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > Post images on http://www.imgur.com and include the link in your
> posting.
> > *****
> >
> > Hi Kyle, Mark,
> >
> > Thanks for your suggestions. Regarding to Kyle's comments/questions:
> >
> > 1) my beam splitter is those cube beam splitter. I should have mentioned
> > that even without beam splitter, when I imaged the collimated beam
> through
> > a lens far away from the collimation lens [between two lenses are just
> two
> > mirrors (1 inch Thorlabs silver protected mirror)], I got similar amount
> of
> > astigmatism. [To Mark: would mirrors usually also cause astigmatism in
> > microscopy? Then does that make sense to use larger mirrors? my beam
> 1/e^2
> > size is about 5 mm in diameter.]
> >
> > 2) the fiber is single moded, and I have tried imaging is using a 150X
> > Nikon objective lens (single lens imaging), and it does not have higher
> > order mode, pretty Gaussian. BTW, imaging with 150X obj. did not give me
> > astigmatism as I moved the fiber (or the camera) back and forth.
> >
> > Besides these, I have another question about astigmatism. Supposed that I
> > have an off-axis lens for the collimation of my Gaussian illumination
> beam,
> > does the amount of astigmatism I will get depend on the distance after
> > which I will image the Gaussian beam?
> >
> > Thanks,
> > Lu
> >
> > -----------------------------------------------------
> > Lu Yan
> > Nanostructured Fibers and Nonlinear Optics Laboratory
> > Electrical and Computer Engineering
> > Boston University
> > 8 St. Mary St., Boston, MA, 02215
> > [phone]
> > [hidden email]
> > -----------------------------------------------------
> >
> > On Wed, Nov 5, 2014 at 3:04 AM, Mark Cannell <[hidden email]
> >
> > wrote:
> >
> >> *****
> >> To join, leave or search the confocal microscopy listserv, go to:
> >> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> >> Post images on http://www.imgur.com and include the link in your
> posting.
> >> *****
> >>
> >> I agree, it could be the mirrors -are they pinched in some way or else
> you
> >> have a lens/source off axis.
> >> HTH
> >>
> >> Mark
> >>
> >> On 5/11/2014, at 7:56 am, Kyle Douglass <[hidden email]> wrote:
> >>
> >>> *****
> >>> To join, leave or search the confocal microscopy listserv, go to:
> >>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> >>> Post images on http://www.imgur.com and include the link in your
> >> posting.
> >>> *****
> >>>
> >>> Hi Lu,
> >>>
> >>>   On 11/05/2014 05:36 AM, Yan, Lu wrote:
> >>>> Hi folks,
> >>>>
> >>>> I am building a fiber based confocal microscopy setup (with sample
> stage
> >>>> scanning). But I always got some astigmatism aberration in PSF
> >> measuremnts.
> >>>> The similar aberration was there even I replaced the objective lens
> >> with a
> >>>> regular lens and imaged my illumination beam through that lens with a
> >>>> camera. I got elongated beam 'spot' on both sides of the focal plane,
> >> and
> >>>> the orientation of the two 'spot' were orthogonal. I think that is
> >>>> astigmatism aberration if I am not mistaken. I draw a schematic in
> >> Evernote
> >>>> so I can include it here. Here is the link:
> >>>>
> >>
> https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
> >>>> (copy and paste if the link does not work in email)
> >>>>
> >>>> I tried to adjust both lens in xy to avoid off-axis incident, but the
> >>>> aberration would go away. So I got confused where they came from. I
> hope
> >>>> someone here could lead me a direction to further look into it.
> >>>>
> >>>> Thanks very much,
> >>>> Lu
> >>> Here are two quick checks that came to mind. Maybe you've tried them,
> >> but it's still good to check all the possible sources of the problem:
> >>>
> >>> 1) Is the beam splitter really a glass cube as it's drawn, or one of
> the
> >> thin dichroic-like beam splitters? Sometimes the thin dichroics are
> >> slightly warped in one direction and can introduce astigmatism after
> >> reflection.
> >>>
> >>> 2) When you illuminate a flat surface or white piece of paper with
> light
> >> directly coming from the single mode fiber, do you see a smooth,
> >> homogeneous intensity distribution or some other kind of structure? I've
> >> noticed that one can occasionally get a weak first-order mode coming
> from
> >> the fiber if the wavelength is close to the multimode cut-on. It may not
> >> necessarily lead to astigmatism, but it's still good to check.
> >>>
> >>> Good luck!
> >>>
> >>> Dr. Kyle Douglass
> >>> The Laboratory of Experimental Biophysics
> >>> EPFL, Lausanne, Switzerland
> >>
> >> Mark  B. Cannell Ph.D. FRSNZ
> >> Professor of Cardiac Cell Biology
> >> School of Physiology &  Pharmacology
> >> Medical Sciences Building
> >> University of Bristol
> >> Bristol
> >> BS8 1TD UK
> >>
> >> [hidden email]
> >>
>

[Lu Yan]

*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
Post images on http://www.imgur.com and include the link in your posting.
*****

Hi everyone,

I have updated the linked page a bit, and included some images I took
yesterday. FYI, the link is:
https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe


Hi Mike,

​I am using a achromat since we will be doing multicolors (in 500~750 nm,
ultimately we would like to build a STED illumination system using
fibers.)​. For the lens orientation, yes I checked that, and there is also
an arrow mark indicating the direction of collimated wavefront on the lens
housing. The problem with the aspheric is that, for multiple colors if I am
not mistaken, I will get significant chromatic aberration provided that my
objective lens (Olympus UPLSAPO 60X) will have quite good correction on
chromatic aberration, i.e. it focuses collimated multiple colors on to the
same focal plane so if I have multiple beams with different divergent
angles it will focus them at different z positions.  So a good achromat
seems the only option.

For the coupler alignment, I am using a throlabs 3-x stage (
https://www.thorlabs.com/thorproduct.cfm?partnumber=MBT616D) with a fiber
holder. I also tried 6-x stage but it does not give me better results. I am
using flat cleaved fiber.

I have updated the linked page and added some images of the beam at
different position in the system. Hope that can clear something out.

Thanks,
Lu

-----------------------------------------------------
Lu Yan
Nanostructured Fibers and Nonlinear Optics Laboratory
Electrical and Computer Engineering
Boston University
8 St. Mary St., Boston, MA, 02215
[phone]
[hidden email]
-----------------------------------------------------

On Wed, Nov 5, 2014 at 1:40 PM, Michael Giacomelli <[hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> Hi Lu,
>
> Regarding your collimator, using short focal length achromats is usually a
> bad idea unless you are using a very broadband laser (E.g. short pulse
> ti:saph or supercontinuum).  Instead, aspheric couplers are usually used as
> an achromat will have significant spherical aberration.  If you do use an
> achromat, make sure that do not use it backwards (always minimize
> glass-wavefront curvature - flatter face into diverging wavefront, curved
> face into collimated wavefront) and if possible simulate in zemax to be
> sure before trying it.  Just simulating the AC254-30-A, putting the lens in
> backwards results in a massively abberated beam.  I would double check that
> first.  Alternatively, buying an aspheric may be a better idea. Technically
> the AC254-30-A is ok, but only just, only if perfectly aligned.  You have
> little margin for error.
>
> If you haven't already, I recommend aligning the coupler to the grid of
> your table, and running the beam quite far out and ensuring that it is
> truly parallel to that grid (and thus perpendicular to lens face).  Because
> of the short focal length, you must be very precise here, with an error of
> about a quarter of a millimeter in centration introducing noticeable
> astigmatism.  I recommend a good 3 axis kinematic.
>
> Regarding tilt of the fiber face, usually fibers are angle cleaved, and
> then mounted in a coupler with a matching tilt.  Make sure that if you used
> an APC fiber, you have an APC mount, and if you used a flat cleaved fiber,
> you have an un-angled mount.
>
> Regarding mirrors, a standard thorlabs mirror used in one of their mounts
> will have negligible astigmatism when used with a beam of your diameter.
> It is true that mirrors can and do introduce aberration into beams, but
> with such a narrow beam diameter, even a relatively poor mirror will not
> introduce noticeable phase error.  These problems are much more common at
> 2" and above.
>
> By the way, do you have access to a beam profiler?  Taking an image of this
> focal spot and posting it might give some clues.
>
> Mike
>
>
>
>
> On Wed, Nov 5, 2014 at 1:11 AM, Yan, Lu <[hidden email]> wrote:
>
> > *****
> > To join, leave or search the confocal microscopy listserv, go to:
> > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > Post images on http://www.imgur.com and include the link in your
> posting.
> > *****
> >
> > Hi Mike,
> >
> > Thanks for promote reply. Like you said for an on axis system (especially
> > simple as mine), astigmatism should not be there, and that why it
> confused
> > me a lot. I am currently using a Thorlabs air-spaced achromatic lens
> > (f=30mm) (
> http://www.thorlabs.com/thorproduct.cfm?partnumber=ACA254-030-A)
> > for the collimation. The fiber I have tried are SMF600 and RBG 400, both
> of
> > which are single mode at 632 nm. I usually looked at the back reflection
> > (from surfaces of the lens) formed interference pattern (concentric
> rings)
> > to align my fiber w.r.t. my fiber facet.
> >
> > For your comments on my questions:
> >
> > 1) I am using the multimode fiber as the pinhole to achieve confocal.
> > 2) Looking at the beam spot after the collimation lens, it was not
> changing
> > much even at several meters away from the lens. The spot changed rapidly
> > around the focal plane if the beam was reimaged through another lens
> (e.g.
> > L2 or L3 in the linked page). I think the NA is large enough for the
> fiber
> > I am using.
> > 3) I was thinking maybe the fiber tip is tilted with respect to the
> > collimation lens plane? Would that cause problem? OR would that still
> give
> > me concentric rings pattern centered at my fiber tip (if the fiber is
> > tilted w.r.t. the lens plane)?
> >
> > Thanks,
> > Lu
> >
> > -----------------------------------------------------
> > Lu Yan
> > Nanostructured Fibers and Nonlinear Optics Laboratory
> > Electrical and Computer Engineering
> > Boston University
> > 8 St. Mary St., Boston, MA, 02215
> > [phone]
> > [hidden email]
> > -----------------------------------------------------
> >
> > On Wed, Nov 5, 2014 at 12:37 AM, Michael Giacomelli <[hidden email]>
> wrote:
> >
> > > *****
> > > To join, leave or search the confocal microscopy listserv, go to:
> > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > Post images on http://www.imgur.com and include the link in your
> > posting.
> > > *****
> > >
> > > Hi Lu,
> > >
> > > In an on axis system like you have drawn there should be no astigmatism
> > if
> > > the fiber is well centered on the optic.  Assuming you've correctly
> > aligned
> > > the collimator, I would think it is some other aberration you are
> seeing.
> > >
> > > Regarding your questions in that linked page:
> > >
> > > 1)  It depends on what you want to collect.  4f (or some other imaging
> > > condition) will give you maximum light collection, which is likely what
> > you
> > > want if you have selected a multimode fiber.  Alternatively, if this
> is a
> > > confocal system, it is probably not necessary.
> > >
> > > 2)  The diagram shows a collimated single mode fiber.  That should be
> > > independent of distance.  If you find that your spot is changing
> rapidly
> > > with distance, likely something is wrong with the collimation.  What
> are
> > > you using a collimator?  Is it suitable for the NA and
> > wavelength/bandwidth
> > > of your source?  Is it well aligned?  What is the exact model of fiber
> > you
> > > are using.
> > >
> > > 3)  Most likely it is a problem with your coupler.
> > >
> > > Mike
> > >
> > > On Tue, Nov 4, 2014 at 11:36 PM, Yan, Lu <[hidden email]> wrote:
> > >
> > > > *****
> > > > To join, leave or search the confocal microscopy listserv, go to:
> > > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > > Post images on http://www.imgur.com and include the link in your
> > > posting.
> > > > *****
> > > >
> > > > Hi folks,
> > > >
> > > > I am building a fiber based confocal microscopy setup (with sample
> > stage
> > > > scanning). But I always got some astigmatism aberration in PSF
> > > measuremnts.
> > > > The similar aberration was there even I replaced the objective lens
> > with
> > > a
> > > > regular lens and imaged my illumination beam through that lens with a
> > > > camera. I got elongated beam 'spot' on both sides of the focal plane,
> > and
> > > > the orientation of the two 'spot' were orthogonal. I think that is
> > > > astigmatism aberration if I am not mistaken. I draw a schematic in
> > > Evernote
> > > > so I can include it here. Here is the link:
> > > >
> > > >
> > >
> >
> https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
> > > > (copy and paste if the link does not work in email)
> > > >
> > > > I tried to adjust both lens in xy to avoid off-axis incident, but the
> > > > aberration would go away. So I got confused where they came from. I
> > hope
> > > > someone here could lead me a direction to further look into it.
> > > >
> > > > Thanks very much,
> > > > Lu
> > > > -----------------------------------------------------
> > > > ​​
> > > >
> > > > Lu Yan
> > > > Nanostructured Fibers and Nonlinear Optics Laboratory
> > > > Electrical and Computer Engineering
> > > > Boston University
> > > > 8 St. Mary St., Boston, MA, 02215
> > > > [phone]
> > > > -----------------------------------------------------
> > > >
> > >
> >
>

[Michael Giacomelli]

*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
Post images on http://www.imgur.com and include the link in your posting.
*****

From your test results, the only components left would be the beam splitter
or the mirrors.  That seems unlikely, but its worth removing each one in
sequence just to be sure you don't have a defective or damaged component
somewhere.

Regarding sted, an achromat is better than a singlet, but probably not
adequate given the large bandwidth you want to use.  I recommend getting a
good microscope objective or even a reflective collimator.  Zemax gives a
0.3 diopter focal shift over that bandwidth for instance.

Mike


On Wed, Nov 5, 2014 at 3:34 PM, Yan, Lu <[hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> Hi everyone,
>
> I have updated the linked page a bit, and included some images I took
> yesterday. FYI, the link is:
>
> https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
>
>
> Hi Mike,
>
> ​I am using a achromat since we will be doing multicolors (in 500~750 nm,
> ultimately we would like to build a STED illumination system using
> fibers.)​. For the lens orientation, yes I checked that, and there is also
> an arrow mark indicating the direction of collimated wavefront on the lens
> housing. The problem with the aspheric is that, for multiple colors if I am
> not mistaken, I will get significant chromatic aberration provided that my
> objective lens (Olympus UPLSAPO 60X) will have quite good correction on
> chromatic aberration, i.e. it focuses collimated multiple colors on to the
> same focal plane so if I have multiple beams with different divergent
> angles it will focus them at different z positions.  So a good achromat
> seems the only option.
>
> For the coupler alignment, I am using a throlabs 3-x stage (
> https://www.thorlabs.com/thorproduct.cfm?partnumber=MBT616D) with a fiber
> holder. I also tried 6-x stage but it does not give me better results. I am
> using flat cleaved fiber.
>
> I have updated the linked page and added some images of the beam at
> different position in the system. Hope that can clear something out.
>
> Thanks,
> Lu
>
> -----------------------------------------------------
> Lu Yan
> Nanostructured Fibers and Nonlinear Optics Laboratory
> Electrical and Computer Engineering
> Boston University
> 8 St. Mary St., Boston, MA, 02215
> [phone]
> [hidden email]
> -----------------------------------------------------
>
> On Wed, Nov 5, 2014 at 1:40 PM, Michael Giacomelli <[hidden email]> wrote:
>
> > *****
> > To join, leave or search the confocal microscopy listserv, go to:
> > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > Post images on http://www.imgur.com and include the link in your
> posting.
> > *****
> >
> > Hi Lu,
> >
> > Regarding your collimator, using short focal length achromats is usually
> a
> > bad idea unless you are using a very broadband laser (E.g. short pulse
> > ti:saph or supercontinuum).  Instead, aspheric couplers are usually used
> as
> > an achromat will have significant spherical aberration.  If you do use an
> > achromat, make sure that do not use it backwards (always minimize
> > glass-wavefront curvature - flatter face into diverging wavefront, curved
> > face into collimated wavefront) and if possible simulate in zemax to be
> > sure before trying it.  Just simulating the AC254-30-A, putting the lens
> in
> > backwards results in a massively abberated beam.  I would double check
> that
> > first.  Alternatively, buying an aspheric may be a better idea.
> Technically
> > the AC254-30-A is ok, but only just, only if perfectly aligned.  You have
> > little margin for error.
> >
> > If you haven't already, I recommend aligning the coupler to the grid of
> > your table, and running the beam quite far out and ensuring that it is
> > truly parallel to that grid (and thus perpendicular to lens face).
> Because
> > of the short focal length, you must be very precise here, with an error
> of
> > about a quarter of a millimeter in centration introducing noticeable
> > astigmatism.  I recommend a good 3 axis kinematic.
> >
> > Regarding tilt of the fiber face, usually fibers are angle cleaved, and
> > then mounted in a coupler with a matching tilt.  Make sure that if you
> used
> > an APC fiber, you have an APC mount, and if you used a flat cleaved
> fiber,
> > you have an un-angled mount.
> >
> > Regarding mirrors, a standard thorlabs mirror used in one of their mounts
> > will have negligible astigmatism when used with a beam of your diameter.
> > It is true that mirrors can and do introduce aberration into beams, but
> > with such a narrow beam diameter, even a relatively poor mirror will not
> > introduce noticeable phase error.  These problems are much more common at
> > 2" and above.
> >
> > By the way, do you have access to a beam profiler?  Taking an image of
> this
> > focal spot and posting it might give some clues.
> >
> > Mike
> >
> >
> >
> >
> > On Wed, Nov 5, 2014 at 1:11 AM, Yan, Lu <[hidden email]> wrote:
> >
> > > *****
> > > To join, leave or search the confocal microscopy listserv, go to:
> > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > Post images on http://www.imgur.com and include the link in your
> > posting.
> > > *****
> > >
> > > Hi Mike,
> > >
> > > Thanks for promote reply. Like you said for an on axis system
> (especially
> > > simple as mine), astigmatism should not be there, and that why it
> > confused
> > > me a lot. I am currently using a Thorlabs air-spaced achromatic lens
> > > (f=30mm) (
> > http://www.thorlabs.com/thorproduct.cfm?partnumber=ACA254-030-A)
> > > for the collimation. The fiber I have tried are SMF600 and RBG 400,
> both
> > of
> > > which are single mode at 632 nm. I usually looked at the back
> reflection
> > > (from surfaces of the lens) formed interference pattern (concentric
> > rings)
> > > to align my fiber w.r.t. my fiber facet.
> > >
> > > For your comments on my questions:
> > >
> > > 1) I am using the multimode fiber as the pinhole to achieve confocal.
> > > 2) Looking at the beam spot after the collimation lens, it was not
> > changing
> > > much even at several meters away from the lens. The spot changed
> rapidly
> > > around the focal plane if the beam was reimaged through another lens
> > (e.g.
> > > L2 or L3 in the linked page). I think the NA is large enough for the
> > fiber
> > > I am using.
> > > 3) I was thinking maybe the fiber tip is tilted with respect to the
> > > collimation lens plane? Would that cause problem? OR would that still
> > give
> > > me concentric rings pattern centered at my fiber tip (if the fiber is
> > > tilted w.r.t. the lens plane)?
> > >
> > > Thanks,
> > > Lu
> > >
> > > -----------------------------------------------------
> > > Lu Yan
> > > Nanostructured Fibers and Nonlinear Optics Laboratory
> > > Electrical and Computer Engineering
> > > Boston University
> > > 8 St. Mary St., Boston, MA, 02215
> > > [phone]
> > > [hidden email]
> > > -----------------------------------------------------
> > >
> > > On Wed, Nov 5, 2014 at 12:37 AM, Michael Giacomelli <[hidden email]>
> > wrote:
> > >
> > > > *****
> > > > To join, leave or search the confocal microscopy listserv, go to:
> > > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > > Post images on http://www.imgur.com and include the link in your
> > > posting.
> > > > *****
> > > >
> > > > Hi Lu,
> > > >
> > > > In an on axis system like you have drawn there should be no
> astigmatism
> > > if
> > > > the fiber is well centered on the optic.  Assuming you've correctly
> > > aligned
> > > > the collimator, I would think it is some other aberration you are
> > seeing.
> > > >
> > > > Regarding your questions in that linked page:
> > > >
> > > > 1)  It depends on what you want to collect.  4f (or some other
> imaging
> > > > condition) will give you maximum light collection, which is likely
> what
> > > you
> > > > want if you have selected a multimode fiber.  Alternatively, if this
> > is a
> > > > confocal system, it is probably not necessary.
> > > >
> > > > 2)  The diagram shows a collimated single mode fiber.  That should be
> > > > independent of distance.  If you find that your spot is changing
> > rapidly
> > > > with distance, likely something is wrong with the collimation.  What
> > are
> > > > you using a collimator?  Is it suitable for the NA and
> > > wavelength/bandwidth
> > > > of your source?  Is it well aligned?  What is the exact model of
> fiber
> > > you
> > > > are using.
> > > >
> > > > 3)  Most likely it is a problem with your coupler.
> > > >
> > > > Mike
> > > >
> > > > On Tue, Nov 4, 2014 at 11:36 PM, Yan, Lu <[hidden email]> wrote:
> > > >
> > > > > *****
> > > > > To join, leave or search the confocal microscopy listserv, go to:
> > > > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > > > Post images on http://www.imgur.com and include the link in your
> > > > posting.
> > > > > *****
> > > > >
> > > > > Hi folks,
> > > > >
> > > > > I am building a fiber based confocal microscopy setup (with sample
> > > stage
> > > > > scanning). But I always got some astigmatism aberration in PSF
> > > > measuremnts.
> > > > > The similar aberration was there even I replaced the objective lens
> > > with
> > > > a
> > > > > regular lens and imaged my illumination beam through that lens
> with a
> > > > > camera. I got elongated beam 'spot' on both sides of the focal
> plane,
> > > and
> > > > > the orientation of the two 'spot' were orthogonal. I think that is
> > > > > astigmatism aberration if I am not mistaken. I draw a schematic in
> > > > Evernote
> > > > > so I can include it here. Here is the link:
> > > > >
> > > > >
> > > >
> > >
> >
> https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
> > > > > (copy and paste if the link does not work in email)
> > > > >
> > > > > I tried to adjust both lens in xy to avoid off-axis incident, but
> the
> > > > > aberration would go away. So I got confused where they came from. I
> > > hope
> > > > > someone here could lead me a direction to further look into it.
> > > > >
> > > > > Thanks very much,
> > > > > Lu
> > > > > -----------------------------------------------------
> > > > > ​​
> > > > >
> > > > > Lu Yan
> > > > > Nanostructured Fibers and Nonlinear Optics Laboratory
> > > > > Electrical and Computer Engineering
> > > > > Boston University
> > > > > 8 St. Mary St., Boston, MA, 02215
> > > > > [phone]
> > > > > -----------------------------------------------------
> > > > >
> > > >
> > >
> >
>

[Tyler Morgus]

*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
Post images on http://www.imgur.com and include the link in your posting.
*****

I can help with the troubleshooting by sending you replacements for any of
the elements that you want to swap out as a way to test if that is the cause
of the aberration.



Tyler

Thorlabs

[Lu Yan]

*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
Post images on http://www.imgur.com and include the link in your posting.
*****

Hi Mike,

You are right that a reflective collimator might be the best option. We
have a reflective collimator (
http://www.thorlabs.com/thorproduct.cfm?partnumber=RC12FC-P01) used in
another project. But the problem with mine is that, we will be using a
specialty designed fiber for the future STED system, and the fiber is not
connectorized (at least not now). We flat cleave the fiber, and put it on a
V-groove fiber holder, but the reflective collimator has a sealed connector
for APC or PC. We used to try to use it but we were never be able to
precisely align the fiber tip w.r.t. the focal point. We also tried a 90
deg off-axis parabolic mirror, but the alignment is so tricky that we could
not get it proper aligned. Thorlabs said they are working on some documents
on the aligning procedure but they have not get back to me since several
month ago.

For the microscope objective, do you have any suggestion which one(s) to
consider? BTW, intermediate optics such as telescope (to change beam size
to match the back aperture of the high NA objective) consisting of two
regular achromats will add chromatic and spherical aberration, right?

Thanks,
Lu

-----------------------------------------------------
Lu Yan
Nanostructured Fibers and Nonlinear Optics Laboratory
Electrical and Computer Engineering
Boston University
8 St. Mary St., Boston, MA, 02215
[phone]
[hidden email]
-----------------------------------------------------

On Wed, Nov 5, 2014 at 5:16 PM, Michael Giacomelli <[hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> From your test results, the only components left would be the beam splitter
> or the mirrors.  That seems unlikely, but its worth removing each one in
> sequence just to be sure you don't have a defective or damaged component
> somewhere.
>
> Regarding sted, an achromat is better than a singlet, but probably not
> adequate given the large bandwidth you want to use.  I recommend getting a
> good microscope objective or even a reflective collimator.  Zemax gives a
> 0.3 diopter focal shift over that bandwidth for instance.
>
> Mike
>
>
> On Wed, Nov 5, 2014 at 3:34 PM, Yan, Lu <[hidden email]> wrote:
>
> > *****
> > To join, leave or search the confocal microscopy listserv, go to:
> > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > Post images on http://www.imgur.com and include the link in your
> posting.
> > *****
> >
> > Hi everyone,
> >
> > I have updated the linked page a bit, and included some images I took
> > yesterday. FYI, the link is:
> >
> >
> https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
> >
> >
> > Hi Mike,
> >
> > ​I am using a achromat since we will be doing multicolors (in 500~750 nm,
> > ultimately we would like to build a STED illumination system using
> > fibers.)​. For the lens orientation, yes I checked that, and there is
> also
> > an arrow mark indicating the direction of collimated wavefront on the
> lens
> > housing. The problem with the aspheric is that, for multiple colors if I
> am
> > not mistaken, I will get significant chromatic aberration provided that
> my
> > objective lens (Olympus UPLSAPO 60X) will have quite good correction on
> > chromatic aberration, i.e. it focuses collimated multiple colors on to
> the
> > same focal plane so if I have multiple beams with different divergent
> > angles it will focus them at different z positions.  So a good achromat
> > seems the only option.
> >
> > For the coupler alignment, I am using a throlabs 3-x stage (
> > https://www.thorlabs.com/thorproduct.cfm?partnumber=MBT616D) with a
> fiber
> > holder. I also tried 6-x stage but it does not give me better results. I
> am
> > using flat cleaved fiber.
> >
> > I have updated the linked page and added some images of the beam at
> > different position in the system. Hope that can clear something out.
> >
> > Thanks,
> > Lu
> >
> > -----------------------------------------------------
> > Lu Yan
> > Nanostructured Fibers and Nonlinear Optics Laboratory
> > Electrical and Computer Engineering
> > Boston University
> > 8 St. Mary St., Boston, MA, 02215
> > [phone]
> > [hidden email]
> > -----------------------------------------------------
> >
> > On Wed, Nov 5, 2014 at 1:40 PM, Michael Giacomelli <[hidden email]> wrote:
> >
> > > *****
> > > To join, leave or search the confocal microscopy listserv, go to:
> > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > Post images on http://www.imgur.com and include the link in your
> > posting.
> > > *****
> > >
> > > Hi Lu,
> > >
> > > Regarding your collimator, using short focal length achromats is
> usually
> > a
> > > bad idea unless you are using a very broadband laser (E.g. short pulse
> > > ti:saph or supercontinuum).  Instead, aspheric couplers are usually
> used
> > as
> > > an achromat will have significant spherical aberration.  If you do use
> an
> > > achromat, make sure that do not use it backwards (always minimize
> > > glass-wavefront curvature - flatter face into diverging wavefront,
> curved
> > > face into collimated wavefront) and if possible simulate in zemax to be
> > > sure before trying it.  Just simulating the AC254-30-A, putting the
> lens
> > in
> > > backwards results in a massively abberated beam.  I would double check
> > that
> > > first.  Alternatively, buying an aspheric may be a better idea.
> > Technically
> > > the AC254-30-A is ok, but only just, only if perfectly aligned.  You
> have
> > > little margin for error.
> > >
> > > If you haven't already, I recommend aligning the coupler to the grid of
> > > your table, and running the beam quite far out and ensuring that it is
> > > truly parallel to that grid (and thus perpendicular to lens face).
> > Because
> > > of the short focal length, you must be very precise here, with an error
> > of
> > > about a quarter of a millimeter in centration introducing noticeable
> > > astigmatism.  I recommend a good 3 axis kinematic.
> > >
> > > Regarding tilt of the fiber face, usually fibers are angle cleaved, and
> > > then mounted in a coupler with a matching tilt.  Make sure that if you
> > used
> > > an APC fiber, you have an APC mount, and if you used a flat cleaved
> > fiber,
> > > you have an un-angled mount.
> > >
> > > Regarding mirrors, a standard thorlabs mirror used in one of their
> mounts
> > > will have negligible astigmatism when used with a beam of your
> diameter.
> > > It is true that mirrors can and do introduce aberration into beams, but
> > > with such a narrow beam diameter, even a relatively poor mirror will
> not
> > > introduce noticeable phase error.  These problems are much more common
> at
> > > 2" and above.
> > >
> > > By the way, do you have access to a beam profiler?  Taking an image of
> > this
> > > focal spot and posting it might give some clues.
> > >
> > > Mike
> > >
> > >
> > >
> > >
> > > On Wed, Nov 5, 2014 at 1:11 AM, Yan, Lu <[hidden email]> wrote:
> > >
> > > > *****
> > > > To join, leave or search the confocal microscopy listserv, go to:
> > > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > > Post images on http://www.imgur.com and include the link in your
> > > posting.
> > > > *****
> > > >
> > > > Hi Mike,
> > > >
> > > > Thanks for promote reply. Like you said for an on axis system
> > (especially
> > > > simple as mine), astigmatism should not be there, and that why it
> > > confused
> > > > me a lot. I am currently using a Thorlabs air-spaced achromatic lens
> > > > (f=30mm) (
> > > http://www.thorlabs.com/thorproduct.cfm?partnumber=ACA254-030-A)
> > > > for the collimation. The fiber I have tried are SMF600 and RBG 400,
> > both
> > > of
> > > > which are single mode at 632 nm. I usually looked at the back
> > reflection
> > > > (from surfaces of the lens) formed interference pattern (concentric
> > > rings)
> > > > to align my fiber w.r.t. my fiber facet.
> > > >
> > > > For your comments on my questions:
> > > >
> > > > 1) I am using the multimode fiber as the pinhole to achieve confocal.
> > > > 2) Looking at the beam spot after the collimation lens, it was not
> > > changing
> > > > much even at several meters away from the lens. The spot changed
> > rapidly
> > > > around the focal plane if the beam was reimaged through another lens
> > > (e.g.
> > > > L2 or L3 in the linked page). I think the NA is large enough for the
> > > fiber
> > > > I am using.
> > > > 3) I was thinking maybe the fiber tip is tilted with respect to the
> > > > collimation lens plane? Would that cause problem? OR would that still
> > > give
> > > > me concentric rings pattern centered at my fiber tip (if the fiber is
> > > > tilted w.r.t. the lens plane)?
> > > >
> > > > Thanks,
> > > > Lu
> > > >
> > > > -----------------------------------------------------
> > > > Lu Yan
> > > > Nanostructured Fibers and Nonlinear Optics Laboratory
> > > > Electrical and Computer Engineering
> > > > Boston University
> > > > 8 St. Mary St., Boston, MA, 02215
> > > > [phone]
> > > > [hidden email]
> > > > -----------------------------------------------------
> > > >
> > > > On Wed, Nov 5, 2014 at 12:37 AM, Michael Giacomelli <[hidden email]>
> > > wrote:
> > > >
> > > > > *****
> > > > > To join, leave or search the confocal microscopy listserv, go to:
> > > > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > > > Post images on http://www.imgur.com and include the link in your
> > > > posting.
> > > > > *****
> > > > >
> > > > > Hi Lu,
> > > > >
> > > > > In an on axis system like you have drawn there should be no
> > astigmatism
> > > > if
> > > > > the fiber is well centered on the optic.  Assuming you've correctly
> > > > aligned
> > > > > the collimator, I would think it is some other aberration you are
> > > seeing.
> > > > >
> > > > > Regarding your questions in that linked page:
> > > > >
> > > > > 1)  It depends on what you want to collect.  4f (or some other
> > imaging
> > > > > condition) will give you maximum light collection, which is likely
> > what
> > > > you
> > > > > want if you have selected a multimode fiber.  Alternatively, if
> this
> > > is a
> > > > > confocal system, it is probably not necessary.
> > > > >
> > > > > 2)  The diagram shows a collimated single mode fiber.  That should
> be
> > > > > independent of distance.  If you find that your spot is changing
> > > rapidly
> > > > > with distance, likely something is wrong with the collimation.
> What
> > > are
> > > > > you using a collimator?  Is it suitable for the NA and
> > > > wavelength/bandwidth
> > > > > of your source?  Is it well aligned?  What is the exact model of
> > fiber
> > > > you
> > > > > are using.
> > > > >
> > > > > 3)  Most likely it is a problem with your coupler.
> > > > >
> > > > > Mike
> > > > >
> > > > > On Tue, Nov 4, 2014 at 11:36 PM, Yan, Lu <[hidden email]> wrote:
> > > > >
> > > > > > *****
> > > > > > To join, leave or search the confocal microscopy listserv, go to:
> > > > > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > > > > Post images on http://www.imgur.com and include the link in your
> > > > > posting.
> > > > > > *****
> > > > > >
> > > > > > Hi folks,
> > > > > >
> > > > > > I am building a fiber based confocal microscopy setup (with
> sample
> > > > stage
> > > > > > scanning). But I always got some astigmatism aberration in PSF
> > > > > measuremnts.
> > > > > > The similar aberration was there even I replaced the objective
> lens
> > > > with
> > > > > a
> > > > > > regular lens and imaged my illumination beam through that lens
> > with a
> > > > > > camera. I got elongated beam 'spot' on both sides of the focal
> > plane,
> > > > and
> > > > > > the orientation of the two 'spot' were orthogonal. I think that
> is
> > > > > > astigmatism aberration if I am not mistaken. I draw a schematic
> in
> > > > > Evernote
> > > > > > so I can include it here. Here is the link:
> > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
> https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
> > > > > > (copy and paste if the link does not work in email)
> > > > > >
> > > > > > I tried to adjust both lens in xy to avoid off-axis incident, but
> > the
> > > > > > aberration would go away. So I got confused where they came
> from. I
> > > > hope
> > > > > > someone here could lead me a direction to further look into it.
> > > > > >
> > > > > > Thanks very much,
> > > > > > Lu
> > > > > > -----------------------------------------------------
> > > > > > ​​
> > > > > >
> > > > > > Lu Yan
> > > > > > Nanostructured Fibers and Nonlinear Optics Laboratory
> > > > > > Electrical and Computer Engineering
> > > > > > Boston University
> > > > > > 8 St. Mary St., Boston, MA, 02215
> > > > > > [phone]
> > > > > > -----------------------------------------------------
> > > > > >
> > > > >
> > > >
> > >
> >
>

[Lu Yan]

*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
Post images on http://www.imgur.com and include the link in your posting.
*****

Hi Tyler,

This is fantastic. It's very kind of you to loan us components for
troubleshooting. I think it will help me a lot.

Thanks a lot,
Lu

-----------------------------------------------------
Lu Yan
Nanostructured Fibers and Nonlinear Optics Laboratory
Electrical and Computer Engineering
Boston University
8 St. Mary St., Boston, MA, 02215
[phone]
[hidden email]
-----------------------------------------------------

On Thu, Nov 6, 2014 at 11:31 AM, Tyler Morgus <[hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> I can help with the troubleshooting by sending you replacements for any of
> the elements that you want to swap out as a way to test if that is the
> cause
> of the aberration.
>
>
>
> Tyler
>
> Thorlabs
>

[Michael Giacomelli]

*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
Post images on http://www.imgur.com and include the link in your posting.
*****

Hi Lu,

For very broadband coupling in the visible, I'm not sure which objectives
would work best.  Most likely a 10x achromatic objective would be fine,
although a fluorite may be needed if you are very sensitive to chromatic
aberration.  I've mostly worked in the NIR however, so I can't recommend
you a specific objective.

The beam expander optics will also introduce aberrations.  How much this
matters depends a lot on what your system will look like.  Unfortunately,
it is very difficult to understand precisely how aberrations will propagate
through a microscope system as objective vendors rarely if ever provide
technical details or model files for their optics.  Fortunately, designing
diffraction limited beam expanders is usually not very difficult.  If you
use relatively long focal length achromats, and use a Galilean expander
(not Keplerian) you will likely be fine. And try to avoid any elements with
focal lengths less than 100 mm (positive or negative).

 If you have access to Zemax however, I recommend simulating to be
certain.  For example, just trying an ACN254-100A and an AC254-200A to
build a 2:1 6 mm to 12 mm expander into a 20x high NA paraxial objective, I
get less than 500 nm of focal shift over your entire range, and 0.013 waves
of spherical aberration (so well below diffraction limited) because the
aberration from the positive and negative elements almost entirely cancels
out.

Mike

On Thu, Nov 6, 2014 at 7:43 PM, Yan, Lu <[hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> Hi Mike,
>
> You are right that a reflective collimator might be the best option. We
> have a reflective collimator (
> http://www.thorlabs.com/thorproduct.cfm?partnumber=RC12FC-P01) used in
> another project. But the problem with mine is that, we will be using a
> specialty designed fiber for the future STED system, and the fiber is not
> connectorized (at least not now). We flat cleave the fiber, and put it on a
> V-groove fiber holder, but the reflective collimator has a sealed connector
> for APC or PC. We used to try to use it but we were never be able to
> precisely align the fiber tip w.r.t. the focal point. We also tried a 90
> deg off-axis parabolic mirror, but the alignment is so tricky that we could
> not get it proper aligned. Thorlabs said they are working on some documents
> on the aligning procedure but they have not get back to me since several
> month ago.
>
> For the microscope objective, do you have any suggestion which one(s) to
> consider? BTW, intermediate optics such as telescope (to change beam size
> to match the back aperture of the high NA objective) consisting of two
> regular achromats will add chromatic and spherical aberration, right?
>
> Thanks,
> Lu
>
> -----------------------------------------------------
> Lu Yan
> Nanostructured Fibers and Nonlinear Optics Laboratory
> Electrical and Computer Engineering
> Boston University
> 8 St. Mary St., Boston, MA, 02215
> [phone]
> [hidden email]
> -----------------------------------------------------
>
> On Wed, Nov 5, 2014 at 5:16 PM, Michael Giacomelli <[hidden email]> wrote:
>
> > *****
> > To join, leave or search the confocal microscopy listserv, go to:
> > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > Post images on http://www.imgur.com and include the link in your
> posting.
> > *****
> >
> > From your test results, the only components left would be the beam
> splitter
> > or the mirrors.  That seems unlikely, but its worth removing each one in
> > sequence just to be sure you don't have a defective or damaged component
> > somewhere.
> >
> > Regarding sted, an achromat is better than a singlet, but probably not
> > adequate given the large bandwidth you want to use.  I recommend getting
> a
> > good microscope objective or even a reflective collimator.  Zemax gives a
> > 0.3 diopter focal shift over that bandwidth for instance.
> >
> > Mike
> >
> >
> > On Wed, Nov 5, 2014 at 3:34 PM, Yan, Lu <[hidden email]> wrote:
> >
> > > *****
> > > To join, leave or search the confocal microscopy listserv, go to:
> > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > Post images on http://www.imgur.com and include the link in your
> > posting.
> > > *****
> > >
> > > Hi everyone,
> > >
> > > I have updated the linked page a bit, and included some images I took
> > > yesterday. FYI, the link is:
> > >
> > >
> >
> https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
> > >
> > >
> > > Hi Mike,
> > >
> > > ​I am using a achromat since we will be doing multicolors (in 500~750
> nm,
> > > ultimately we would like to build a STED illumination system using
> > > fibers.)​. For the lens orientation, yes I checked that, and there is
> > also
> > > an arrow mark indicating the direction of collimated wavefront on the
> > lens
> > > housing. The problem with the aspheric is that, for multiple colors if
> I
> > am
> > > not mistaken, I will get significant chromatic aberration provided that
> > my
> > > objective lens (Olympus UPLSAPO 60X) will have quite good correction on
> > > chromatic aberration, i.e. it focuses collimated multiple colors on to
> > the
> > > same focal plane so if I have multiple beams with different divergent
> > > angles it will focus them at different z positions.  So a good achromat
> > > seems the only option.
> > >
> > > For the coupler alignment, I am using a throlabs 3-x stage (
> > > https://www.thorlabs.com/thorproduct.cfm?partnumber=MBT616D) with a
> > fiber
> > > holder. I also tried 6-x stage but it does not give me better results.
> I
> > am
> > > using flat cleaved fiber.
> > >
> > > I have updated the linked page and added some images of the beam at
> > > different position in the system. Hope that can clear something out.
> > >
> > > Thanks,
> > > Lu
> > >
> > > -----------------------------------------------------
> > > Lu Yan
> > > Nanostructured Fibers and Nonlinear Optics Laboratory
> > > Electrical and Computer Engineering
> > > Boston University
> > > 8 St. Mary St., Boston, MA, 02215
> > > [phone]
> > > [hidden email]
> > > -----------------------------------------------------
> > >
> > > On Wed, Nov 5, 2014 at 1:40 PM, Michael Giacomelli <[hidden email]>
> wrote:
> > >
> > > > *****
> > > > To join, leave or search the confocal microscopy listserv, go to:
> > > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > > Post images on http://www.imgur.com and include the link in your
> > > posting.
> > > > *****
> > > >
> > > > Hi Lu,
> > > >
> > > > Regarding your collimator, using short focal length achromats is
> > usually
> > > a
> > > > bad idea unless you are using a very broadband laser (E.g. short
> pulse
> > > > ti:saph or supercontinuum).  Instead, aspheric couplers are usually
> > used
> > > as
> > > > an achromat will have significant spherical aberration.  If you do
> use
> > an
> > > > achromat, make sure that do not use it backwards (always minimize
> > > > glass-wavefront curvature - flatter face into diverging wavefront,
> > curved
> > > > face into collimated wavefront) and if possible simulate in zemax to
> be
> > > > sure before trying it.  Just simulating the AC254-30-A, putting the
> > lens
> > > in
> > > > backwards results in a massively abberated beam.  I would double
> check
> > > that
> > > > first.  Alternatively, buying an aspheric may be a better idea.
> > > Technically
> > > > the AC254-30-A is ok, but only just, only if perfectly aligned.  You
> > have
> > > > little margin for error.
> > > >
> > > > If you haven't already, I recommend aligning the coupler to the grid
> of
> > > > your table, and running the beam quite far out and ensuring that it
> is
> > > > truly parallel to that grid (and thus perpendicular to lens face).
> > > Because
> > > > of the short focal length, you must be very precise here, with an
> error
> > > of
> > > > about a quarter of a millimeter in centration introducing noticeable
> > > > astigmatism.  I recommend a good 3 axis kinematic.
> > > >
> > > > Regarding tilt of the fiber face, usually fibers are angle cleaved,
> and
> > > > then mounted in a coupler with a matching tilt.  Make sure that if
> you
> > > used
> > > > an APC fiber, you have an APC mount, and if you used a flat cleaved
> > > fiber,
> > > > you have an un-angled mount.
> > > >
> > > > Regarding mirrors, a standard thorlabs mirror used in one of their
> > mounts
> > > > will have negligible astigmatism when used with a beam of your
> > diameter.
> > > > It is true that mirrors can and do introduce aberration into beams,
> but
> > > > with such a narrow beam diameter, even a relatively poor mirror will
> > not
> > > > introduce noticeable phase error.  These problems are much more
> common
> > at
> > > > 2" and above.
> > > >
> > > > By the way, do you have access to a beam profiler?  Taking an image
> of
> > > this
> > > > focal spot and posting it might give some clues.
> > > >
> > > > Mike
> > > >
> > > >
> > > >
> > > >
> > > > On Wed, Nov 5, 2014 at 1:11 AM, Yan, Lu <[hidden email]> wrote:
> > > >
> > > > > *****
> > > > > To join, leave or search the confocal microscopy listserv, go to:
> > > > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > > > Post images on http://www.imgur.com and include the link in your
> > > > posting.
> > > > > *****
> > > > >
> > > > > Hi Mike,
> > > > >
> > > > > Thanks for promote reply. Like you said for an on axis system
> > > (especially
> > > > > simple as mine), astigmatism should not be there, and that why it
> > > > confused
> > > > > me a lot. I am currently using a Thorlabs air-spaced achromatic
> lens
> > > > > (f=30mm) (
> > > > http://www.thorlabs.com/thorproduct.cfm?partnumber=ACA254-030-A)
> > > > > for the collimation. The fiber I have tried are SMF600 and RBG 400,
> > > both
> > > > of
> > > > > which are single mode at 632 nm. I usually looked at the back
> > > reflection
> > > > > (from surfaces of the lens) formed interference pattern (concentric
> > > > rings)
> > > > > to align my fiber w.r.t. my fiber facet.
> > > > >
> > > > > For your comments on my questions:
> > > > >
> > > > > 1) I am using the multimode fiber as the pinhole to achieve
> confocal.
> > > > > 2) Looking at the beam spot after the collimation lens, it was not
> > > > changing
> > > > > much even at several meters away from the lens. The spot changed
> > > rapidly
> > > > > around the focal plane if the beam was reimaged through another
> lens
> > > > (e.g.
> > > > > L2 or L3 in the linked page). I think the NA is large enough for
> the
> > > > fiber
> > > > > I am using.
> > > > > 3) I was thinking maybe the fiber tip is tilted with respect to the
> > > > > collimation lens plane? Would that cause problem? OR would that
> still
> > > > give
> > > > > me concentric rings pattern centered at my fiber tip (if the fiber
> is
> > > > > tilted w.r.t. the lens plane)?
> > > > >
> > > > > Thanks,
> > > > > Lu
> > > > >
> > > > > -----------------------------------------------------
> > > > > Lu Yan
> > > > > Nanostructured Fibers and Nonlinear Optics Laboratory
> > > > > Electrical and Computer Engineering
> > > > > Boston University
> > > > > 8 St. Mary St., Boston, MA, 02215
> > > > > [phone]
> > > > > [hidden email]
> > > > > -----------------------------------------------------
> > > > >
> > > > > On Wed, Nov 5, 2014 at 12:37 AM, Michael Giacomelli <[hidden email]>
> > > > wrote:
> > > > >
> > > > > > *****
> > > > > > To join, leave or search the confocal microscopy listserv, go to:
> > > > > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > > > > Post images on http://www.imgur.com and include the link in your
> > > > > posting.
> > > > > > *****
> > > > > >
> > > > > > Hi Lu,
> > > > > >
> > > > > > In an on axis system like you have drawn there should be no
> > > astigmatism
> > > > > if
> > > > > > the fiber is well centered on the optic.  Assuming you've
> correctly
> > > > > aligned
> > > > > > the collimator, I would think it is some other aberration you are
> > > > seeing.
> > > > > >
> > > > > > Regarding your questions in that linked page:
> > > > > >
> > > > > > 1)  It depends on what you want to collect.  4f (or some other
> > > imaging
> > > > > > condition) will give you maximum light collection, which is
> likely
> > > what
> > > > > you
> > > > > > want if you have selected a multimode fiber.  Alternatively, if
> > this
> > > > is a
> > > > > > confocal system, it is probably not necessary.
> > > > > >
> > > > > > 2)  The diagram shows a collimated single mode fiber.  That
> should
> > be
> > > > > > independent of distance.  If you find that your spot is changing
> > > > rapidly
> > > > > > with distance, likely something is wrong with the collimation.
> > What
> > > > are
> > > > > > you using a collimator?  Is it suitable for the NA and
> > > > > wavelength/bandwidth
> > > > > > of your source?  Is it well aligned?  What is the exact model of
> > > fiber
> > > > > you
> > > > > > are using.
> > > > > >
> > > > > > 3)  Most likely it is a problem with your coupler.
> > > > > >
> > > > > > Mike
> > > > > >
> > > > > > On Tue, Nov 4, 2014 at 11:36 PM, Yan, Lu <[hidden email]> wrote:
> > > > > >
> > > > > > > *****
> > > > > > > To join, leave or search the confocal microscopy listserv, go
> to:
> > > > > > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > > > > > Post images on http://www.imgur.com and include the link in
> your
> > > > > > posting.
> > > > > > > *****
> > > > > > >
> > > > > > > Hi folks,
> > > > > > >
> > > > > > > I am building a fiber based confocal microscopy setup (with
> > sample
> > > > > stage
> > > > > > > scanning). But I always got some astigmatism aberration in PSF
> > > > > > measuremnts.
> > > > > > > The similar aberration was there even I replaced the objective
> > lens
> > > > > with
> > > > > > a
> > > > > > > regular lens and imaged my illumination beam through that lens
> > > with a
> > > > > > > camera. I got elongated beam 'spot' on both sides of the focal
> > > plane,
> > > > > and
> > > > > > > the orientation of the two 'spot' were orthogonal. I think that
> > is
> > > > > > > astigmatism aberration if I am not mistaken. I draw a schematic
> > in
> > > > > > Evernote
> > > > > > > so I can include it here. Here is the link:
> > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
> https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
> > > > > > > (copy and paste if the link does not work in email)
> > > > > > >
> > > > > > > I tried to adjust both lens in xy to avoid off-axis incident,
> but
> > > the
> > > > > > > aberration would go away. So I got confused where they came
> > from. I
> > > > > hope
> > > > > > > someone here could lead me a direction to further look into it.
> > > > > > >
> > > > > > > Thanks very much,
> > > > > > > Lu
> > > > > > > -----------------------------------------------------
> > > > > > > ​​
> > > > > > >
> > > > > > > Lu Yan
> > > > > > > Nanostructured Fibers and Nonlinear Optics Laboratory
> > > > > > > Electrical and Computer Engineering
> > > > > > > Boston University
> > > > > > > 8 St. Mary St., Boston, MA, 02215
> > > > > > > [phone]
> > > > > > > -----------------------------------------------------
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>

[Craig Brideau]

*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
Post images on http://www.imgur.com and include the link in your posting.
*****

Fiber collimation tricky, and short focal length achromats are very
sensitive to any misalignment. As has already been mentioned, make sure you
have the flat side of the lens towards the fiber. Slight tilts or XY
displacements can lead to 'interesting' beam profiles. As your sketches
show, you don't seem to have any issues when you look at the beam after the
collimator, but sometimes you need to let the beam propagate a while before
any astigmatism will become obvious. I usually shoot a beam from a
collimator a significant distance, at least several meters, and check the
beam all along the path. When I am convinced I have a correctly collimated
and gaussian beam, then I put my other optics into the path.

Craig Brideau

On Thu, Nov 6, 2014 at 8:01 PM, Michael Giacomelli <[hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> Hi Lu,
>
> For very broadband coupling in the visible, I'm not sure which objectives
> would work best.  Most likely a 10x achromatic objective would be fine,
> although a fluorite may be needed if you are very sensitive to chromatic
> aberration.  I've mostly worked in the NIR however, so I can't recommend
> you a specific objective.
>
> The beam expander optics will also introduce aberrations.  How much this
> matters depends a lot on what your system will look like.  Unfortunately,
> it is very difficult to understand precisely how aberrations will propagate
> through a microscope system as objective vendors rarely if ever provide
> technical details or model files for their optics.  Fortunately, designing
> diffraction limited beam expanders is usually not very difficult.  If you
> use relatively long focal length achromats, and use a Galilean expander
> (not Keplerian) you will likely be fine. And try to avoid any elements with
> focal lengths less than 100 mm (positive or negative).
>
>  If you have access to Zemax however, I recommend simulating to be
> certain.  For example, just trying an ACN254-100A and an AC254-200A to
> build a 2:1 6 mm to 12 mm expander into a 20x high NA paraxial objective, I
> get less than 500 nm of focal shift over your entire range, and 0.013 waves
> of spherical aberration (so well below diffraction limited) because the
> aberration from the positive and negative elements almost entirely cancels
> out.
>
> Mike
>
> On Thu, Nov 6, 2014 at 7:43 PM, Yan, Lu <[hidden email]> wrote:
>
> > *****
> > To join, leave or search the confocal microscopy listserv, go to:
> > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > Post images on http://www.imgur.com and include the link in your
> posting.
> > *****
> >
> > Hi Mike,
> >
> > You are right that a reflective collimator might be the best option. We
> > have a reflective collimator (
> > http://www.thorlabs.com/thorproduct.cfm?partnumber=RC12FC-P01) used in
> > another project. But the problem with mine is that, we will be using a
> > specialty designed fiber for the future STED system, and the fiber is not
> > connectorized (at least not now). We flat cleave the fiber, and put it
> on a
> > V-groove fiber holder, but the reflective collimator has a sealed
> connector
> > for APC or PC. We used to try to use it but we were never be able to
> > precisely align the fiber tip w.r.t. the focal point. We also tried a 90
> > deg off-axis parabolic mirror, but the alignment is so tricky that we
> could
> > not get it proper aligned. Thorlabs said they are working on some
> documents
> > on the aligning procedure but they have not get back to me since several
> > month ago.
> >
> > For the microscope objective, do you have any suggestion which one(s) to
> > consider? BTW, intermediate optics such as telescope (to change beam size
> > to match the back aperture of the high NA objective) consisting of two
> > regular achromats will add chromatic and spherical aberration, right?
> >
> > Thanks,
> > Lu
> >
> > -----------------------------------------------------
> > Lu Yan
> > Nanostructured Fibers and Nonlinear Optics Laboratory
> > Electrical and Computer Engineering
> > Boston University
> > 8 St. Mary St., Boston, MA, 02215
> > [phone]
> > [hidden email]
> > -----------------------------------------------------
> >
> > On Wed, Nov 5, 2014 at 5:16 PM, Michael Giacomelli <[hidden email]> wrote:
> >
> > > *****
> > > To join, leave or search the confocal microscopy listserv, go to:
> > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > Post images on http://www.imgur.com and include the link in your
> > posting.
> > > *****
> > >
> > > From your test results, the only components left would be the beam
> > splitter
> > > or the mirrors.  That seems unlikely, but its worth removing each one
> in
> > > sequence just to be sure you don't have a defective or damaged
> component
> > > somewhere.
> > >
> > > Regarding sted, an achromat is better than a singlet, but probably not
> > > adequate given the large bandwidth you want to use.  I recommend
> getting
> > a
> > > good microscope objective or even a reflective collimator.  Zemax
> gives a
> > > 0.3 diopter focal shift over that bandwidth for instance.
> > >
> > > Mike
> > >
> > >
> > > On Wed, Nov 5, 2014 at 3:34 PM, Yan, Lu <[hidden email]> wrote:
> > >
> > > > *****
> > > > To join, leave or search the confocal microscopy listserv, go to:
> > > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > > Post images on http://www.imgur.com and include the link in your
> > > posting.
> > > > *****
> > > >
> > > > Hi everyone,
> > > >
> > > > I have updated the linked page a bit, and included some images I took
> > > > yesterday. FYI, the link is:
> > > >
> > > >
> > >
> >
> https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
> > > >
> > > >
> > > > Hi Mike,
> > > >
> > > > ​I am using a achromat since we will be doing multicolors (in 500~750
> > nm,
> > > > ultimately we would like to build a STED illumination system using
> > > > fibers.)​. For the lens orientation, yes I checked that, and there is
> > > also
> > > > an arrow mark indicating the direction of collimated wavefront on the
> > > lens
> > > > housing. The problem with the aspheric is that, for multiple colors
> if
> > I
> > > am
> > > > not mistaken, I will get significant chromatic aberration provided
> that
> > > my
> > > > objective lens (Olympus UPLSAPO 60X) will have quite good correction
> on
> > > > chromatic aberration, i.e. it focuses collimated multiple colors on
> to
> > > the
> > > > same focal plane so if I have multiple beams with different divergent
> > > > angles it will focus them at different z positions.  So a good
> achromat
> > > > seems the only option.
> > > >
> > > > For the coupler alignment, I am using a throlabs 3-x stage (
> > > > https://www.thorlabs.com/thorproduct.cfm?partnumber=MBT616D) with a
> > > fiber
> > > > holder. I also tried 6-x stage but it does not give me better
> results.
> > I
> > > am
> > > > using flat cleaved fiber.
> > > >
> > > > I have updated the linked page and added some images of the beam at
> > > > different position in the system. Hope that can clear something out.
> > > >
> > > > Thanks,
> > > > Lu
> > > >
> > > > -----------------------------------------------------
> > > > Lu Yan
> > > > Nanostructured Fibers and Nonlinear Optics Laboratory
> > > > Electrical and Computer Engineering
> > > > Boston University
> > > > 8 St. Mary St., Boston, MA, 02215
> > > > [phone]
> > > > [hidden email]
> > > > -----------------------------------------------------
> > > >
> > > > On Wed, Nov 5, 2014 at 1:40 PM, Michael Giacomelli <[hidden email]>
> > wrote:
> > > >
> > > > > *****
> > > > > To join, leave or search the confocal microscopy listserv, go to:
> > > > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > > > Post images on http://www.imgur.com and include the link in your
> > > > posting.
> > > > > *****
> > > > >
> > > > > Hi Lu,
> > > > >
> > > > > Regarding your collimator, using short focal length achromats is
> > > usually
> > > > a
> > > > > bad idea unless you are using a very broadband laser (E.g. short
> > pulse
> > > > > ti:saph or supercontinuum).  Instead, aspheric couplers are usually
> > > used
> > > > as
> > > > > an achromat will have significant spherical aberration.  If you do
> > use
> > > an
> > > > > achromat, make sure that do not use it backwards (always minimize
> > > > > glass-wavefront curvature - flatter face into diverging wavefront,
> > > curved
> > > > > face into collimated wavefront) and if possible simulate in zemax
> to
> > be
> > > > > sure before trying it.  Just simulating the AC254-30-A, putting the
> > > lens
> > > > in
> > > > > backwards results in a massively abberated beam.  I would double
> > check
> > > > that
> > > > > first.  Alternatively, buying an aspheric may be a better idea.
> > > > Technically
> > > > > the AC254-30-A is ok, but only just, only if perfectly aligned.
> You
> > > have
> > > > > little margin for error.
> > > > >
> > > > > If you haven't already, I recommend aligning the coupler to the
> grid
> > of
> > > > > your table, and running the beam quite far out and ensuring that it
> > is
> > > > > truly parallel to that grid (and thus perpendicular to lens face).
> > > > Because
> > > > > of the short focal length, you must be very precise here, with an
> > error
> > > > of
> > > > > about a quarter of a millimeter in centration introducing
> noticeable
> > > > > astigmatism.  I recommend a good 3 axis kinematic.
> > > > >
> > > > > Regarding tilt of the fiber face, usually fibers are angle cleaved,
> > and
> > > > > then mounted in a coupler with a matching tilt.  Make sure that if
> > you
> > > > used
> > > > > an APC fiber, you have an APC mount, and if you used a flat cleaved
> > > > fiber,
> > > > > you have an un-angled mount.
> > > > >
> > > > > Regarding mirrors, a standard thorlabs mirror used in one of their
> > > mounts
> > > > > will have negligible astigmatism when used with a beam of your
> > > diameter.
> > > > > It is true that mirrors can and do introduce aberration into beams,
> > but
> > > > > with such a narrow beam diameter, even a relatively poor mirror
> will
> > > not
> > > > > introduce noticeable phase error.  These problems are much more
> > common
> > > at
> > > > > 2" and above.
> > > > >
> > > > > By the way, do you have access to a beam profiler?  Taking an image
> > of
> > > > this
> > > > > focal spot and posting it might give some clues.
> > > > >
> > > > > Mike
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > On Wed, Nov 5, 2014 at 1:11 AM, Yan, Lu <[hidden email]> wrote:
> > > > >
> > > > > > *****
> > > > > > To join, leave or search the confocal microscopy listserv, go to:
> > > > > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > > > > Post images on http://www.imgur.com and include the link in your
> > > > > posting.
> > > > > > *****
> > > > > >
> > > > > > Hi Mike,
> > > > > >
> > > > > > Thanks for promote reply. Like you said for an on axis system
> > > > (especially
> > > > > > simple as mine), astigmatism should not be there, and that why it
> > > > > confused
> > > > > > me a lot. I am currently using a Thorlabs air-spaced achromatic
> > lens
> > > > > > (f=30mm) (
> > > > > http://www.thorlabs.com/thorproduct.cfm?partnumber=ACA254-030-A)
> > > > > > for the collimation. The fiber I have tried are SMF600 and RBG
> 400,
> > > > both
> > > > > of
> > > > > > which are single mode at 632 nm. I usually looked at the back
> > > > reflection
> > > > > > (from surfaces of the lens) formed interference pattern
> (concentric
> > > > > rings)
> > > > > > to align my fiber w.r.t. my fiber facet.
> > > > > >
> > > > > > For your comments on my questions:
> > > > > >
> > > > > > 1) I am using the multimode fiber as the pinhole to achieve
> > confocal.
> > > > > > 2) Looking at the beam spot after the collimation lens, it was
> not
> > > > > changing
> > > > > > much even at several meters away from the lens. The spot changed
> > > > rapidly
> > > > > > around the focal plane if the beam was reimaged through another
> > lens
> > > > > (e.g.
> > > > > > L2 or L3 in the linked page). I think the NA is large enough for
> > the
> > > > > fiber
> > > > > > I am using.
> > > > > > 3) I was thinking maybe the fiber tip is tilted with respect to
> the
> > > > > > collimation lens plane? Would that cause problem? OR would that
> > still
> > > > > give
> > > > > > me concentric rings pattern centered at my fiber tip (if the
> fiber
> > is
> > > > > > tilted w.r.t. the lens plane)?
> > > > > >
> > > > > > Thanks,
> > > > > > Lu
> > > > > >
> > > > > > -----------------------------------------------------
> > > > > > Lu Yan
> > > > > > Nanostructured Fibers and Nonlinear Optics Laboratory
> > > > > > Electrical and Computer Engineering
> > > > > > Boston University
> > > > > > 8 St. Mary St., Boston, MA, 02215
> > > > > > [phone]
> > > > > > [hidden email]
> > > > > > -----------------------------------------------------
> > > > > >
> > > > > > On Wed, Nov 5, 2014 at 12:37 AM, Michael Giacomelli <
> [hidden email]>
> > > > > wrote:
> > > > > >
> > > > > > > *****
> > > > > > > To join, leave or search the confocal microscopy listserv, go
> to:
> > > > > > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > > > > > Post images on http://www.imgur.com and include the link in
> your
> > > > > > posting.
> > > > > > > *****
> > > > > > >
> > > > > > > Hi Lu,
> > > > > > >
> > > > > > > In an on axis system like you have drawn there should be no
> > > > astigmatism
> > > > > > if
> > > > > > > the fiber is well centered on the optic.  Assuming you've
> > correctly
> > > > > > aligned
> > > > > > > the collimator, I would think it is some other aberration you
> are
> > > > > seeing.
> > > > > > >
> > > > > > > Regarding your questions in that linked page:
> > > > > > >
> > > > > > > 1)  It depends on what you want to collect.  4f (or some other
> > > > imaging
> > > > > > > condition) will give you maximum light collection, which is
> > likely
> > > > what
> > > > > > you
> > > > > > > want if you have selected a multimode fiber.  Alternatively, if
> > > this
> > > > > is a
> > > > > > > confocal system, it is probably not necessary.
> > > > > > >
> > > > > > > 2)  The diagram shows a collimated single mode fiber.  That
> > should
> > > be
> > > > > > > independent of distance.  If you find that your spot is
> changing
> > > > > rapidly
> > > > > > > with distance, likely something is wrong with the collimation.
> > > What
> > > > > are
> > > > > > > you using a collimator?  Is it suitable for the NA and
> > > > > > wavelength/bandwidth
> > > > > > > of your source?  Is it well aligned?  What is the exact model
> of
> > > > fiber
> > > > > > you
> > > > > > > are using.
> > > > > > >
> > > > > > > 3)  Most likely it is a problem with your coupler.
> > > > > > >
> > > > > > > Mike
> > > > > > >
> > > > > > > On Tue, Nov 4, 2014 at 11:36 PM, Yan, Lu <[hidden email]> wrote:
> > > > > > >
> > > > > > > > *****
> > > > > > > > To join, leave or search the confocal microscopy listserv, go
> > to:
> > > > > > > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > > > > > > Post images on http://www.imgur.com and include the link in
> > your
> > > > > > > posting.
> > > > > > > > *****
> > > > > > > >
> > > > > > > > Hi folks,
> > > > > > > >
> > > > > > > > I am building a fiber based confocal microscopy setup (with
> > > sample
> > > > > > stage
> > > > > > > > scanning). But I always got some astigmatism aberration in
> PSF
> > > > > > > measuremnts.
> > > > > > > > The similar aberration was there even I replaced the
> objective
> > > lens
> > > > > > with
> > > > > > > a
> > > > > > > > regular lens and imaged my illumination beam through that
> lens
> > > > with a
> > > > > > > > camera. I got elongated beam 'spot' on both sides of the
> focal
> > > > plane,
> > > > > > and
> > > > > > > > the orientation of the two 'spot' were orthogonal. I think
> that
> > > is
> > > > > > > > astigmatism aberration if I am not mistaken. I draw a
> schematic
> > > in
> > > > > > > Evernote
> > > > > > > > so I can include it here. Here is the link:
> > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
> https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
> > > > > > > > (copy and paste if the link does not work in email)
> > > > > > > >
> > > > > > > > I tried to adjust both lens in xy to avoid off-axis incident,
> > but
> > > > the
> > > > > > > > aberration would go away. So I got confused where they came
> > > from. I
> > > > > > hope
> > > > > > > > someone here could lead me a direction to further look into
> it.
> > > > > > > >
> > > > > > > > Thanks very much,
> > > > > > > > Lu
> > > > > > > > -----------------------------------------------------
> > > > > > > > ​​
> > > > > > > >
> > > > > > > > Lu Yan
> > > > > > > > Nanostructured Fibers and Nonlinear Optics Laboratory
> > > > > > > > Electrical and Computer Engineering
> > > > > > > > Boston University
> > > > > > > > 8 St. Mary St., Boston, MA, 02215
> > > > > > > > [phone]
> > > > > > > > -----------------------------------------------------
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>