http://confocal-microscopy-list.275.s1.nabble.com/Astigmatism-aberration-as-a-function-of-distance-tp7582827p7582840.html
yesterday. FYI, the link is:
fibers.). For the lens orientation, yes I checked that, and there is also
housing. The problem with the aspheric is that, for multiple colors if I am
chromatic aberration, i.e. it focuses collimated multiple colors on to the
angles it will focus them at different z positions. So a good achromat
holder. I also tried 6-x stage but it does not give me better results. I am
different position in the system. Hope that can clear something out.
8 St. Mary St., Boston, MA, 02215
> *****
> 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
> > (617)353-0286
> >
[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
> > > > (617)353-0286
> > > > -----------------------------------------------------
> > > >
> > >
> >
>