Validation of a generalized laser safety analysis method for irregular pulse trains

Abstract

The current laser safety standards do not address specifically how to account for repetitively pulsed lasers with irregular pulse trains. Variations in peak power, pulse duration, and duty cycle within a pulse train pose a number of problems when it comes to product classification or to assess the hazard of a given exposure. This study proposes to analyze irregular pulse trains by generalizing the determination of the number of pulses N used in the IEC 60825-1 or n in the ANSI Z136.1 standard. The proposed method for the determination of N applies to emission durations longer than 5 μs and was validated by generating a large number of theoretical pulse patterns and by comparing the retinal injury threshold, determined with a computer model, with the applicable emission limit. For 18 000 different pulse patterns, the ratio of the injury threshold to the emission limit was never less than 2, which is commonly considered as a sufficient safety margin. The smallest safety margin found for regular pulse patterns also equals 2. This study validates an analysis method for irregular pulse trains that can be included in the standards by simple generalization of the determination of the parameter N.