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