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Hi Dan,

Permissible to who?

Once you reach fluorophore saturation there is no need to go higher 
for confocal (I believe SHG and THG doe not saturate). So, if laser 
power X and X+10% (i.e. 90 and 100% AOTF setting) give equal 
brightness (assuming PMT gain not trivially saturated), then X is saturated.

If your 543 nm laser routinely achieves fluorophore saturation, let's trade.

If a 1k x 1k scan takes 1 second, pixel dwell time is 1 usecond or 
less (ignoring spot size wrt Nyquist), so your 10 us is an over-estimate.

George
p.s. of course if you want to use saturation to achieve 
ultramicroscopy resolutions (Gustafsson, et al for example), then 
X+20% might be better than X.


At 11:33 AM 7/7/2008, you wrote:
>Search the CONFOCAL archive at
>http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>
>Dear all,
>
>Recently I was calculating the maximum permissible exposure (MPE) power
>level for confocal or multiphoton microscopy for tissue imaging. It seems to
>me that currently the optical power used by most confocal or multiphoton
>studies in tissue imaging far exceeds the MPE limit. Here is how I
>calculated it and please tell me if I am doing something wrong. The
>literature I have found so far do not talk about tight focusing.
>
>According to the ANSI-Z136.1 standard, in the NIR range with an exposure
>time of 10^-7 to 10 second, the MPE level is 0.56*t^0.25, t being the pixel
>dwelling time. Considering a typical pixel dwelling time at 10 microsecond,
>the MPE level is 31 mJ/cm-2. Assume we have a focal spot size of 1 micron,
>the average power should be 0.31 nJ or 0.031 mW. That seems like an awfully
>small number considering a few mW (even tens of mW) is routinely used in
>human skin imaging.
>
>If some one has worked on this before, please advise me what is wrong here.
>Thank you very much for your input.
>
>Dan Fu






George McNamara, Ph.D.
University of Miami, Miller School of Medicine
Image Core
Miami, FL 33010
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