Liquid light guides for lasers?

[Matthew Nicholas-2]

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Dear list,
I'm wondering if anyone has any experience using liquid light guides with
lasers? In particular, I'm interested in what the beam profile exiting the
fiber typically looks like (assuming a Gaussian/TEM_00 input), and whether
the emitted light is still spatially coherent. Any experience anyone could
share (including products with which you've had success) would be quite
helpful and much appreciated! I'd also be very interested if anyone can
suggest a good reference on optical properties of liquid light guides that
includes discussion of laser applications. So far, I have not been able to
find much, and unfortunately I have zero personal experience in this area.

Thanks in advance for any help you can offer,
Matt

--
Matthew Nicholas
Medical Scientist Training Program Student
Laboratory of Arne Gennerich
Department of Anatomy and Structural Biology
Albert Einstein College of Medicine
Forchheimer Building, Room 628
1300 Morris Park Avenue
Bronx, New York 10461
718.430.3446
[hidden email]

[Zdenek Svindrych]

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Dear Matt,

I don't have much experience using LLGs with lasers... But as fat as I know
you can get TEM00 only from a single mode fiber (that is some five to ten
microns in diameter). With thicker fibers more modes can propagate and the
output beam profile depends on which modes you excite, e.g. it depends on
the angle of input beam. The far filed output of a 300 micron (pretty thick)
fiber can easily look like a ring with dark center.

With LLGs it's even more severe, as they are far thicker (3 to 5
millimeters). You may try it yourself by shooting your cheap green pointer
(these usually have surprisingly nice mode structure, crapped only by the
plastic lenses inside) into an LLG. The output is far from gaussian...

Still there is some coherence in the output, and probably you'll get a lot
of speckle. It depends on your application, but most of the time it is not
practical to use LLGs with lasers. You loose all the nice features lasers
(diffraction-limited performance) and the bad features remain (speckle).

So, the last bit: Why do you want that?

Cheers,
zdenek svindrych



---------- Původní zpráva ----------
Od: Matthew Nicholas <[hidden email]>
Datum: 19. 7. 2013
Předmět: Liquid light guides for lasers?

"*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
*****

Dear list,
I'm wondering if anyone has any experience using liquid light guides with
lasers? In particular, I'm interested in what the beam profile exiting the
fiber typically looks like (assuming a Gaussian/TEM_00 input), and whether
the emitted light is still spatially coherent. Any experience anyone could
share (including products with which you've had success) would be quite
helpful and much appreciated! I'd also be very interested if anyone can
suggest a good reference on optical properties of liquid light guides that
includes discussion of laser applications. So far, I have not been able to
find much, and unfortunately I have zero personal experience in this area.

Thanks in advance for any help you can offer,
Matt

--
Matthew Nicholas
Medical Scientist Training Program Student
Laboratory of Arne Gennerich
Department of Anatomy and Structural Biology
Albert Einstein College of Medicine
Forchheimer Building, Room 628
1300 Morris Park Avenue
Bronx, New York 10461
718.430.3446
[hidden email]"

[Matthew Nicholas-2]

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 Thanks very much for the information, Zdenek. Based on the behavior of
multimode fibers you mentioned, I wondered whether  LLGs might exhibit
similar behavior. I'm actually interested in how lasers propagate through
LLGs in relation to illumination for widefield fluorescence microscopy
(TIRFM, to be specific). We have a setup with multiple lasers, which we
currently plan to guide through a broadband, single-mode fiber in order to
clean up the beam profiles (i.e. using the fiber as a spatial filter),
followed by collimation with a parabolic mirror. However, the power
capacity of the fiber is somewhat limited, and it's been my impression that
LLGs have far better throughput efficiency, at least for noncoherent,
extended sources like lamps (perhaps specifically because LLGs support
multiple transverse modes?). In addition, the Guassian profile is actually
somewhat undesirable, since it does not provide even illumination without
substantial beam expansion (and thus loss of significant power density in
the object field). I was doing some research on beam shaping and came
across a couple references that seemed to suggest the output of a LLG is
more uniform (i.e. a "top-hat" distribution, rather than Gaussian), and
that LLGs tend to eliminate coherence, e.g.
http://www.microscopyu.com/articles/livecellimaging/automaticmicroscope.html:

"The most widely used and practical method of coupling a light source to
the microscope, while also reducing coherence, is to focus the light into a
flexible length of single-mode optical fiber or a liquid light guide (see
Figure 9). Thermal motion in the liquid light guide constantly alters the
optical path and scatters light so that both spatial and temporal coherence
are effectively eliminated. In the case of a coiled single-mode optical
fiber, the cladding reflections constantly change because the fiber flexes
slightly, producing an exit beam that is effectively uniform in intensity
over time and space. The technique of vibrating the fiber (at a frequency
of up to 100 kilohertz) is also effective in scrambling the light. The
light phase is scrambled due to the varying path lengths of light waves
passing through the fiber, although the high radiance and monochromaticity
are preserved. The exit beam is described by a *top-hat* intensity profile
rather than the Gaussian profile that is characteristic of laser light...."

So basically I was wondering if a LLG might provide more even illumination
and fewer interference effects (speckle, etc.). My intuition told me "no,"
especially since I've never seen this done by others, but I was curious.
Thanks very much for sharing your experience.

Cheers,
Matt

On 7/20/2013 1:48 AM, Zdenek Svindrych wrote:

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Dear Matt,

I don't have much experience using LLGs with lasers... But as fat as I know
you can get TEM00 only from a single mode fiber (that is some five to ten
microns in diameter). With thicker fibers more modes can propagate and the
output beam profile depends on which modes you excite, e.g. it depends on
the angle of input beam. The far filed output of a 300 micron (pretty thick)
fiber can easily look like a ring with dark center.

With LLGs it's even more severe, as they are far thicker (3 to 5
millimeters). You may try it yourself by shooting your cheap green pointer
(these usually have surprisingly nice mode structure, crapped only by the
plastic lenses inside) into an LLG. The output is far from gaussian...

Still there is some coherence in the output, and probably you'll get a lot
of speckle. It depends on your application, but most of the time it is not
practical to use LLGs with lasers. You loose all the nice features lasers
(diffraction-limited performance) and the bad features remain (speckle).

So, the last bit: Why do you want that?

Cheers,
zdenek svindrych



---------- Původní zpráva ----------
Od: Matthew Nicholas <[hidden email]>
<[hidden email]>
Datum: 19. 7. 2013
Předmět: Liquid light guides for lasers?

"*****
To join, leave or search the confocal microscopy listserv, go
to:http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
*****

Dear list,
I'm wondering if anyone has any experience using liquid light guides with
lasers? In particular, I'm interested in what the beam profile exiting the
fiber typically looks like (assuming a Gaussian/TEM_00 input), and whether
the emitted light is still spatially coherent. Any experience anyone could
share (including products with which you've had success) would be quite
helpful and much appreciated! I'd also be very interested if anyone can
suggest a good reference on optical properties of liquid light guides that
includes discussion of laser applications. So far, I have not been able to
find much, and unfortunately I have zero personal experience in this area.

Thanks in advance for any help you can offer,
Matt

[Craig Brideau]

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The light guide is acting somewhat like a Homogenizing Rod:

http://www.edmundoptics.com/optics/prisms/light-pipes-homogenizing-rods/tapered-light-pipe-homogenizing-rods/3071

The width of the guide allows light to 'rattle around' inside of it which
eliminates structure and coherence in the light.  The end result is a
relatively flat output.  Coupling the lasers in via single mode sounds like
a bit of a waste; I'd just try expanding the beams out to a bit smaller
than the light guide diameter and just fire them into the end of it.  If
your guide is long enough and has some gentle bends in it, you should seem
some cleanup, in theory.

Craig Brideau
Hotchkiss Brain Institute
University of Calgary



On Mon, Jul 22, 2013 at 1:56 PM, Matthew Nicholas <
[hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
>  Thanks very much for the information, Zdenek. Based on the behavior of
> multimode fibers you mentioned, I wondered whether  LLGs might exhibit
> similar behavior. I'm actually interested in how lasers propagate through
> LLGs in relation to illumination for widefield fluorescence microscopy
> (TIRFM, to be specific). We have a setup with multiple lasers, which we
> currently plan to guide through a broadband, single-mode fiber in order to
> clean up the beam profiles (i.e. using the fiber as a spatial filter),
> followed by collimation with a parabolic mirror. However, the power
> capacity of the fiber is somewhat limited, and it's been my impression that
> LLGs have far better throughput efficiency, at least for noncoherent,
> extended sources like lamps (perhaps specifically because LLGs support
> multiple transverse modes?). In addition, the Guassian profile is actually
> somewhat undesirable, since it does not provide even illumination without
> substantial beam expansion (and thus loss of significant power density in
> the object field). I was doing some research on beam shaping and came
> across a couple references that seemed to suggest the output of a LLG is
> more uniform (i.e. a "top-hat" distribution, rather than Gaussian), and
> that LLGs tend to eliminate coherence, e.g.
>
> http://www.microscopyu.com/articles/livecellimaging/automaticmicroscope.html
> :
>
> "The most widely used and practical method of coupling a light source to
> the microscope, while also reducing coherence, is to focus the light into a
> flexible length of single-mode optical fiber or a liquid light guide (see
> Figure 9). Thermal motion in the liquid light guide constantly alters the
> optical path and scatters light so that both spatial and temporal coherence
> are effectively eliminated. In the case of a coiled single-mode optical
> fiber, the cladding reflections constantly change because the fiber flexes
> slightly, producing an exit beam that is effectively uniform in intensity
> over time and space. The technique of vibrating the fiber (at a frequency
> of up to 100 kilohertz) is also effective in scrambling the light. The
> light phase is scrambled due to the varying path lengths of light waves
> passing through the fiber, although the high radiance and monochromaticity
> are preserved. The exit beam is described by a *top-hat* intensity profile
> rather than the Gaussian profile that is characteristic of laser light...."
>
> So basically I was wondering if a LLG might provide more even illumination
> and fewer interference effects (speckle, etc.). My intuition told me "no,"
> especially since I've never seen this done by others, but I was curious.
> Thanks very much for sharing your experience.
>
> Cheers,
> Matt
>
> On 7/20/2013 1:48 AM, Zdenek Svindrych wrote:
>
> *****
> To join, leave or search the confocal microscopy listserv, go
> to:http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> Dear Matt,
>
> I don't have much experience using LLGs with lasers... But as fat as I know
> you can get TEM00 only from a single mode fiber (that is some five to ten
> microns in diameter). With thicker fibers more modes can propagate and the
> output beam profile depends on which modes you excite, e.g. it depends on
> the angle of input beam. The far filed output of a 300 micron (pretty
> thick)
> fiber can easily look like a ring with dark center.
>
> With LLGs it's even more severe, as they are far thicker (3 to 5
> millimeters). You may try it yourself by shooting your cheap green pointer
> (these usually have surprisingly nice mode structure, crapped only by the
> plastic lenses inside) into an LLG. The output is far from gaussian...
>
> Still there is some coherence in the output, and probably you'll get a lot
> of speckle. It depends on your application, but most of the time it is not
> practical to use LLGs with lasers. You loose all the nice features lasers
> (diffraction-limited performance) and the bad features remain (speckle).
>
> So, the last bit: Why do you want that?
>
> Cheers,
> zdenek svindrych
>
>
>
> ---------- Původní zpráva ----------
> Od: Matthew Nicholas <[hidden email]>
> <[hidden email]>
> Datum: 19. 7. 2013
> Předmět: Liquid light guides for lasers?
>
> "*****
> To join, leave or search the confocal microscopy listserv, go
> to:http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> Dear list,
> I'm wondering if anyone has any experience using liquid light guides with
> lasers? In particular, I'm interested in what the beam profile exiting the
> fiber typically looks like (assuming a Gaussian/TEM_00 input), and whether
> the emitted light is still spatially coherent. Any experience anyone could
> share (including products with which you've had success) would be quite
> helpful and much appreciated! I'd also be very interested if anyone can
> suggest a good reference on optical properties of liquid light guides that
> includes discussion of laser applications. So far, I have not been able to
> find much, and unfortunately I have zero personal experience in this area.
>
> Thanks in advance for any help you can offer,
> Matt
>

[Zdenek Svindrych]

*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
*****

Hi Matthew,
a single mode fiber is a good choice for TIRFM. The power is not limited by
the fiber itself, you can get Watts of power through. The problem is
coupling the lasers - it is very delicate and tedious to couple several
lasers into SM fiber. Moreover, if you use strong lasers with ugly profile,
you won't get much power through the fiber, only the "TEM00 part of the
beam" finds its way into the fiber.

Coupling to LLG is much easier, you can couple more than million times more
light from your arc lamp into an LLG than into a SM fiber. But you only
delay your problem a bit, as you also need to couple the light into an
objective...

This is where "etendue" or, in 1D, Abbe sine condition enters the game. Abbe
says that the product of NA and the diameter of the FOV (or the source
diameter) is a constant in good optical systems. Consider an 100x 1.45NA
objective with FOV diameter 200um. In normal fluorescence you can use
smaller NA for illumination, so you can couple for example a very thick
fiber (600um, 0.22NA) without loosing any light. But if you use LLG (3mm
daimeter, 0.5NA), then you are either overfilling your objective or
illuminating larger FOV than the objective can support; in either case you
utilize less than 10% (my math may be wrong here) of the light. (Btw, can
anyone explain WHY the LLGs are being used in the first place?)

With TIRF illumination the situation is even worse, of course. With an arc
lamp you have no option but to block the center of the illumination beam and
use only the thin ring of NAs (e.g. from 1.35 to 1.45) for illumination.
This will cost you another 85% of the light that could pass the objective.
With a SM fiber you use only single tiny spot at the edge of the back
aperture of the objective, effectively using all the light from the fiber. I
would consider a thin multimode fiber (50um or 62.5um, 0.22NA, common in
telecom applications), which, when properly focused (I would prefer critical
illumination to Koehler, it is simpler and more efficient) needs only 5% (in
1D sense) of the above mentioned objective NA for efficient illumination
which should just fit the TIRF range of NA.

So the bottom line is: don't use LLG as it spreads the beam too much. If SM
fiber is too thin for laser coupling, try some reasonable MM fiber. You don'
t need so much power for widefield (unless you want to try STORM/PALM/GSDIM/
whatever-the-name). To get rid of the speckles you probably need to
constantly agitate the MM fiber, and you would probably need to shake with
the LLG as well. To get better idea shoot some laser into your LLG, try some
lenses and MM fibers. Pencil, ruler and a paper are indispensable as well.

Good luck with your project,
cheers,
zdenek


---------- Původní zpráva ----------
Od: Matthew Nicholas <[hidden email]>
Datum: 22. 7. 2013
Předmět: Re: Liquid light guides for lasers?

"*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
*****

Thanks very much for the information, Zdenek. Based on the behavior of
multimode fibers you mentioned, I wondered whether LLGs might exhibit
similar behavior. I'm actually interested in how lasers propagate through
LLGs in relation to illumination for widefield fluorescence microscopy
(TIRFM, to be specific). We have a setup with multiple lasers, which we
currently plan to guide through a broadband, single-mode fiber in order to
clean up the beam profiles (i.e. using the fiber as a spatial filter),
followed by collimation with a parabolic mirror. However, the power
capacity of the fiber is somewhat limited, and it's been my impression that
LLGs have far better throughput efficiency, at least for noncoherent,
extended sources like lamps (perhaps specifically because LLGs support
multiple transverse modes?). In addition, the Guassian profile is actually
somewhat undesirable, since it does not provide even illumination without
substantial beam expansion (and thus loss of significant power density in
the object field). I was doing some research on beam shaping and came
across a couple references that seemed to suggest the output of a LLG is
more uniform (i.e. a "top-hat" distribution, rather than Gaussian), and
that LLGs tend to eliminate coherence, e.g.
http://www.microscopyu.com/articles/livecellimaging/automaticmicroscope.
html:

"The most widely used and practical method of coupling a light source to
the microscope, while also reducing coherence, is to focus the light into a
flexible length of single-mode optical fiber or a liquid light guide (see
Figure 9). Thermal motion in the liquid light guide constantly alters the
optical path and scatters light so that both spatial and temporal coherence
are effectively eliminated. In the case of a coiled single-mode optical
fiber, the cladding reflections constantly change because the fiber flexes
slightly, producing an exit beam that is effectively uniform in intensity
over time and space. The technique of vibrating the fiber (at a frequency
of up to 100 kilohertz) is also effective in scrambling the light. The
light phase is scrambled due to the varying path lengths of light waves
passing through the fiber, although the high radiance and monochromaticity
are preserved. The exit beam is described by a *top-hat* intensity profile
rather than the Gaussian profile that is characteristic of laser light...."

So basically I was wondering if a LLG might provide more even illumination
and fewer interference effects (speckle, etc.). My intuition told me "no,"
especially since I've never seen this done by others, but I was curious.
Thanks very much for sharing your experience.

Cheers,
Matt

On 7/20/2013 1:48 AM, Zdenek Svindrych wrote:

*****
To join, leave or search the confocal microscopy listserv, go
to:http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
*****

Dear Matt,

I don't have much experience using LLGs with lasers... But as fat as I know
you can get TEM00 only from a single mode fiber (that is some five to ten
microns in diameter). With thicker fibers more modes can propagate and the
output beam profile depends on which modes you excite, e.g. it depends on
the angle of input beam. The far filed output of a 300 micron (pretty thick)
fiber can easily look like a ring with dark center.

With LLGs it's even more severe, as they are far thicker (3 to 5
millimeters). You may try it yourself by shooting your cheap green pointer
(these usually have surprisingly nice mode structure, crapped only by the
plastic lenses inside) into an LLG. The output is far from gaussian...

Still there is some coherence in the output, and probably you'll get a lot
of speckle. It depends on your application, but most of the time it is not
practical to use LLGs with lasers. You loose all the nice features lasers
(diffraction-limited performance) and the bad features remain (speckle).

So, the last bit: Why do you want that?

Cheers,
zdenek svindrych



---------- Původní zpráva ----------
Od: Matthew Nicholas <[hidden email]>
<[hidden email]>
Datum: 19. 7. 2013
Předmět: Liquid light guides for lasers?

"*****
To join, leave or search the confocal microscopy listserv, go
to:http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
*****

Dear list,
I'm wondering if anyone has any experience using liquid light guides with
lasers? In particular, I'm interested in what the beam profile exiting the
fiber typically looks like (assuming a Gaussian/TEM_00 input), and whether
the emitted light is still spatially coherent. Any experience anyone could
share (including products with which you've had success) would be quite
helpful and much appreciated! I'd also be very interested if anyone can
suggest a good reference on optical properties of liquid light guides that
includes discussion of laser applications. So far, I have not been able to
find much, and unfortunately I have zero personal experience in this area.

Thanks in advance for any help you can offer,
Matt"