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Hi Guy,

This is something I've been meaning to test by rep rate
doubling/quadrupling our Chameleon and doing SNR measurements.  Its
hard to say from a theoretical point of view which would be better.
Certainly higher rep rate gives you lower multiphoton absorption
probability per unit power, but you don't make as effective use of the
detector dynamic range. Another thing on my mind is that my
(admittedly unscientific) impression is that images taken at low
numbers of pulses per pixel (1-2) tend to be fairly grainy no matter
how high the illumination power, although I've never been entirely
clear what that mechanism would be or if its somehow specific to my
samples.

Mike

On Sun, Jan 11, 2015 at 3:42 AM, Guy Cox <[log in to unmask]> wrote:
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> 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.
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>
> I've changed the title since the previous one was going in too many directions.  Jim P mentioned that in conventional 2P microscopy we have ~12ns between pulses so with a typical fluorescence lifetime of 2-4ns we have some dead time.  Actually I'm not sure that's a bad thing since getting another hit on a molecule that's already excited is likely to increase bleaching.  And do remember the lifetime is not when fluorescence stops - just when it falls to 1/e of the original intensity, so there's still some to go.
>
> However I recall seeing at conferences much smaller femtosecond lasers with, naturally, much faster repetition rates.  (The physical size of the laser determines the rep rate since it is the time light takes to go round one circuit of the cavity).  These would completely eliminate the dead time.  So has anyone used these for microscopy?
>
>                         Guy
>
> Guy Cox, Honorary Associate Professor
> School of Medical Sciences
>
> Australian Centre for Microscopy and Microanalysis,
> Madsen, F09, University of Sydney, NSW 2006