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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