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Dispersion also is not the full story, as non-linear frquency generation
cannot be compensated with "chirping". A rule of thumb is if you keep the
average power of an 80 fs, 80 MHz pulsetrain below 20 mW through a 15 cm
coupling fiber, you will get away with prechirping (or end up with 1ps
pulses, which may be acceptable under some circumstances). New holey
fibers may give you solitonic solutions to your problems (Gaeta
and coworkers,Science, Vol 301, Issue 5640, 1702-1704), but that may be
considered too exotic at the moment.
Sudipta

On Tue, 16 Mar 2004, Guy Cox wrote:

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> http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>
> You face fundamental problems trying to do this.  Because of
> dispersion in the fibre your pulse will spread out considerably.
> Zeiss tried to get around this with a prechirp unit (introducing
> reverse dspersion before it enters the fibre) but it was a pain
> to align and they soon gave it up.  The reason Leica can do it
> with a picosecond laser is that there is a much smaller wavelength
> spread so although the pulse starts out longer it doesn't spread
> out as much.
>
> Your best (and cheapest) option is to buy a suitable optical
> table and mount everything on it.
>
>                                                 Guy
>
>
> >
> >Is there anybody out there who has experience with coupling a Mira 900 into
> >an optical fibre for two photon applications?
> >
> >We're using a Coherent Mira 900 to do 2P microscopy on our Leica SP2. The
> >laser beam is coupled in directly to the scan head. But the Setup is a bit
> >different from the Leica-standard: The laser and the microscope are not
> >placed on the same optical table. The tables are connected in a quite rigid
> >way but adjustment of the laser is not very stable and needs fine tuning
> >before each imaging session (far from beeing comfortable and user friendly).
> >Also our beam profile is very bad - I think - because of the slightly more
> >complicated beam path and the increased distance between laser and scanner.
> >Therefore, I'm thinking about getting the laser fibre-copuled so that I
> >don't have to worry any more about moving tables. The Leica system for fibre
> >coupling works only with picosecond-pulse compatible fibres, they say. (Is
> >there a good single mode fibre for a femtosecond pulsed laser at all?)
> >Picosecond pulses obviously are a great drawback for 2P microscopy if
> >penetration depth into the sample is an issue. That's bad for us because we
> >would like to image quite thick tissue. On the other hand, a better beam
> >profile and a more homogeneous illumination of the objective back aperture
> >should result in a better-defined focus and better 2P excitation, hopefully
> >requiring less laser power. (?) I'm not really sure which way to go...
> >
> >The guys from Leica are really helpful... But before changing our setup I
> >would like to make up my mind if it is worth trading pulse width for stable
> >adjustment and clean focus. (Unfortunately there is no way to mount the
> >laser on the same table as the microscope.)
> >
> >Anybody with experience in similar issues who could give some input?
> >Thanks for any help!
> >
> >Best Regards,
> >
> >Olaf
> >
> >
> >--
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> >| Dr. Olaf Selchow                                      |
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> >| University of Stuttgart                               |
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> >| T: +49 711 685 8209, Fax: +49 711 685 7484         |
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>
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