Section B : M.P.E. evaluation in the case or repeated laser pulses
Basics : It is much more difficult to evaluate the M.P.E. for a pulsed laser, because of the limited amount of existing data on the exposure to multiple pulses. One must thus be cautious when evaluating the exposure to repeated pulses. In order to determine the M.P.E. for repeated pulses, the method is the following :
The M.P.E. for wavelengths in the range 400 to 1400 nm must be determined using the most restrictive of the following instructions, depending on the specific case :
- the exposure to one isolated pulse of the pulse train mustn't exceed the M.P.E.
- the mean intensity for a pulse train of duration T mustn't exceed the M.P.E. defined in the tables for one isolated pulse of duration T.
- the exposure to one pulse from the pulse train mustn't exceed the M.P.E. specified for an isolated pulse, multiplied by the total number of pulses during the exposure duration to the power of -1/4 :
At any wavelength outside this range, the M.P.E. for skin and eyes must be determined using the most restrictive instructions.
Question
Using both your own knowledge and the table given in appendix 3 (at the end of the exercises), what is the M.P.E. for an eye submitted to laser radiation at 488 nm from an Argon laser, emitting pulses of 10 ns at a repetition rate of 1 MHz ? The evaluation of this M.P.E. can be done using two different approaches. One will be less restricting, and the other one, more rigorous, will give the exact M.P.E. value.