Dear laser ranging colleagues,

On Thursday's session in Riga, we heard a few talks and comments on eye safety issues. I knew almost nothing about MPE (Maximum permissible exposure) and want to learn a bit.

I was wondering how difficult/realistic it will be to make the energy density low enough (as intended in SLR2000). But I have a question: in what time window(s) should we worry about our eyes?

I found it hard to understand IEC 60825 even in the Japanese translation, but some of the charts in this wikipedia page is partly understandable (but not sure if trustable).

https://en.wikipedia.org/wiki/Laser_safetyLet me try to understand by assuming two lasers:

(H) Herstmonceux's: 532 nm, 0.5 mJ, 2 kHz, 10 ps FWHM, beam diameter 3 cm

(S) Stuttgart's: 1064 nm, 0.3 mJ, 10 kHz, 3 ns FWHM, beam diameter 7 cm

(1) Energy per pulse

I guess this chart

https://en.wikipedia.org/wiki/Laser_safety#/media/File:IEC60825_MPE_J_nm.png

caption: "MPE as energy density versus wavelength for various exposure times (pulse durations)"

is the one to look at. We can read the MPEs at:

MPE for (H) = 1e-8 J/cm^2 (where real (H) = 7e-5 J/cm^2)

MPE for (S) = 2e-6 J/cm^2 (where real (S) = 8e-6 J/cm^2)

so Herstmonceux's pulse is far from eye safety but Stuttgart's is close to eye safety considering the fibre loss.

(2) Energy per longer time span (but how long?)

John Degnan commented that the IR could be dangerous because we cannot see it and the eyes can be exposed for a longer time.

I am not sure but is this chart

https://en.wikipedia.org/wiki/Laser_safety#/media/File:IEC60825_MPE_J_s.png

caption: "Maximum permissible exposure (MPE) at the cornea for a collimated laser beam according to IEC 60825, as energy density versus exposure time for various wavelengths"useful for this? Then, we can read at 1 sec (correct?):

MPE for (H) = 2e-3 J/cm^2 (where real (H) = 0.14e J/cm^2)

MPE for (S) = 1e-2 J/cm^2 (where real (S) = 8e-2 J/cm^2)

again a similar story as above.

Is my understanding correct? Can Stuttgart SLR be declared as an eye-safe system by reducing the energy a bit and/or by making the beam aperture large?

Or, if you know the best MPE expert in this community, I would like to contact him/her.

Toshi