Damage thresholds for irregularly pulsed exposure of the retina

Abstract

The international laser safety standard IEC 60825-1 in its second edition does not provide a method on how to analyse pulse trains with irregular pulse peak powers. A retinal thermal injury model is used to study examples of pulse trains with irregular peak powers. It is shown that if an individual pulse is only a factor of 1.5 higher in power than the other pulses of the train, for the conditions studied (small source, 532 nm wavelength, cooling between pulses) the retinal damage is induced solely by the one higher pulse and the other pulses do not contribute to the damage process. For this case, the N−1/4 rule is overrestrictive and the Total-On-Time-Pulse rule can seriously understimate the risk and shall not be applied to analyse pulse trains with varying pulse peak power. As any standardised method to analyse irregular pulse patterns that will be developed in the future will be rather a worst case approach, the retinal thermal damage model developed by the Austrian Research Centers Seibersdorf can be used as a validated tool for hazard analysis of specific emission patterns for pulse durations in the millisecond regime.The international laser safety standard IEC 60825-1 in its second edition does not provide a method on how to analyse pulse trains with irregular pulse peak powers. A retinal thermal injury model is used to study examples of pulse trains with irregular peak powers. It is shown that if an individual pulse is only a factor of 1.5 higher in power than the other pulses of the train, for the conditions studied (small source, 532 nm wavelength, cooling between pulses) the retinal damage is induced solely by the one higher pulse and the other pulses do not contribute to the damage process. For this case, the N−1/4 rule is overrestrictive and the Total-On-Time-Pulse rule can seriously understimate the risk and shall not be applied to analyse pulse trains with varying pulse peak power. As any standardised method to analyse irregular pulse patterns that will be developed in the future will be rather a worst case approach, the retinal thermal damage model developed by the Austrian Research Centers Seibersdorf can be...