http://confocal-microscopy-list.275.s1.nabble.com/Liquid-light-guides-for-lasers-tp7580735p7580740.html
eliminates structure and coherence in the light. The end result is a
relatively flat output. Coupling the lasers in via single mode sounds like
than the light guide diameter and just fire them into the end of it. If
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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?
>
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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
>