Johannes has already answered the beam properties question pretty well.
However, you should realize that a short length, e.g. inches, of "big"
(multimode) fiber will have minimal impact on the beam quality unless you
bend it sharply.  The extent of "mode mixing" over length will vary with a
number of parameters.  You may well be able to use a meter of multimode UV
grade fused silica and tolerate the impact on beam quality.

Before further discussion on the UV capabilities of fibers, other waveguides
or broadband sources (e.g. Xenon lamps) I need to know just what wavelengths
at which you want to work.  On the capabilities of UV grade fused silica
(quartz) fibers you might call Polymicro Technologies (602-375-4100).  They
have about the best specifications that I have seen, as of a year ago.
However the smallest core size is 50 microns, which is very "multimode".

Realize that lamps are BIG broadband sources.  A 150 W Xenon lamp will
deliver ~ 30 mW out of its F1 condenser in a 10 nm band near 550 nm.  This
will be in about a 3 degree full width cone at ~ 35 mm diameter.  You want
to illuminate a ~1E-3 mm spot with ~ 150 degree cone (high NA objective).
Ignoring immersion optics, Fresnel losses, etc. you can deliver at best ~
1/1,000 of that light (look up the First Order or LaGrange Invariant in
geometric optics or the Brightness Theorem in physical optics).  If you
start with a lamp be sure you a <= 10 uW is enough light for you in the
exposure times of interest.  Note: I use a Hg arc for fluorescence
excitation in the near UV, down to about 275 nm.  I couple it through a
liquid waveguide since it has higher energy transfer efficiency than the UV
fused silica waveguides.  However, in this case I illuminate a "spot" of >
100 um diameter.  Even at ~300 um diameter I throw a lot of light away from
my arc lamp.

Others have mentioned fast shutters from Vincent Associates.  NM Laser makes
some electro-mechanical shutters that are faster and still in the ~$1K
range.  If you use EO or AO modulators you may need several to cover the
UV-visible region.

---------------------------------------
At 10:12 PM 2/25/97 -0500, you wrote:
>Dear All:
>
>Thanks for all of your various inputs.  However helpful they have been,
>I am a silly, big-haired girl and need some more assistance.  First, I
>think that I really must make clear what I am thinking about doing in
>the experiment, although I do believe it is clear to you all.  The idea is
>to focus a beam (cone if inevitable) of light as the STIMULUS for a
>small region of a cell, or at least a single cell and then use the CLSM
>to measure real-time responses (if any) in the illuminated cells.  Our
>interest is in the UV range and although it would be the best of all
>worlds to be completely monochromatic, a narrow (2-10 nm) would
>suffice at least for pilot studies.  My hair requires that I ask of you all
>to help me with the following:
>
>1) What precisely do you mean when you say that the beam properties
>    will be no longer as they began after a trip through the fiber optic?
>    I hate to be obtuse but I need a more exact explanation (again due
>    to the density of my hair)
>2) What are the characteristics of these rumored UV-capable (fused silica
>    fiber optics?  Johannes - you can just give me the references
>3) Does the following sound practical/possible/adequate...
>
>I was thinking of a light source of wide range (Xenon, etc) followed (in
>the light path) by a set of interference and neutral density filters to select
>wavelength and adjust intensity of the light.  Then this would be collected
>with a suitable fiber optic (fused silica?) that would end in a light guide
>which is tapered at the end - similar to a patch-pipette.  This is then held
>by a micromanipulator and "focussed" onto the cell(s).  This is in use
>with some investigators doing another thing with visible range light.
>
>My Questions:
>
>1) Can I use a conventional fiber optic in this system?
>2) If not, what is required?
>3) Can I do something to avoid the use of the micromanipulator via
>     an actuated dual-shutter to rapidly switch from the stimulating "beam"
>     to the excitation beam of the CLSM?  (This would of course be through
>     the objective of the scope)
>
>We'll have a Bar-B-Q after my Nobel Prize if you help me.
>
>Susi
>
>

Neal Nicklaus
Senior Scientist
SEQ Limited

Voice:  609-452-6033 Ext. 13
Fax:    609-452-5955
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