Product Code: ILSC2007_203

Repetitive Pulses and Laser-induced Retinal Injury Thresholds
Authors:
David Lund, USAMRD-WRAIR; Brooks AFB TX USA
Presented at ILSC 2007

Experimental studies with repetitively pulsed lasers show that the ED50, expressed as energy per pulse, varies as the inverse fourth power of the number of pulses in the exposure, relatively independently of the wavelength, pulse duration, or pulse repetition frequency of the laser. Models based on a thermal damage mechanism cannot readily explain this result. Menendez et. al. proposed a probability-summation model for predicting the threshold for a train of pulses based on the probit statistics for a single pulse and assuming that each pulse is an independent trial, The requirement that the effect of each pulse in the pulse train be unaffected by the effects of other pulses in the train is a showstopper when the end effect is viewed as a thermal effect with each pulse in the train contributing to the end temperature of the target tissue. There is evidence that the induction of cell death by microcavitation bubbles around melanin granules heated by incident laser irradiation can satisfy the condition of pulse independence as required by the probability summation model. This paper will summarize the experimental data and discuss the relevance of the probability summation model given microcavitation as a damage mechanism.