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Hi George,

Sorry I wasn't being clear in the original post. Maximum Permissible
Exposure (MPE) is a term used in the American National Standard for Safe Use
of Lasers (ANSI Z136.1). When confocal or multiphoton microscopy is used in
human skin imaging, I assume the standard for skin exposure should also be
followed. 

In both reflectance Confocal laser scanning microscopy and multiphoton
microscopy of human skin (in vivo), the optical power used are usually more
than 10 mW with very tight focusing condition. I am not sure about the
saturation problem you mentioned, but I would think that the only reason to
use higher power is to increase the signal to noise ratio. The pixel time
can be reduced to 1 microsecond, but even with that number, the calculated
MPE is 0.17 mW. This means that the routine skin imaging conditon of
confocal or multiphoton is way above the national safety standard. 

I am interested in knowing whether there is anything wrong in my calculation
or if the national standard is inappropriate in this case.

For reference in reflectance confocal or multiphoton, see
1.	Langley, R. G. B.; Rajadhyaksha, M. et. al., Journal of the American
Academy of Dermatology 2001, 45, (3), 365-376.
2.	Konig, K.; Riemann, I. et. al.,Journal of Biomedical Optics 2003, 8, (3),
432-439.

Regards,
Dan