EPITHELIAL DAMAGE THRESHOLDS FOR SEQUENCES OF 80 NS PULSES OF 10.6 MU-M LASER-RADIATION

Infrared radiation from a CO2 laser operating at 10.6 mu m is almost t otally absorbed by the tear him and corneal epithelium. Epithelial dam age thresholds for single and multiple pulse exposures have been well characterized for exposures having pulse durations greater than or equ al to 1 ms and a few damage thresholds have been reported for much sho rter duration pulses. However until recently, no studies have been don e to determine damage thresholds from sequences of very short pulses. The purpose of this study is to begin to fill this gap. New Zealand wh ite rabbit corneas were exposed to sequences of 80 ns pulses from a CO 2-TEA laser operating in the (TEM)(00) mode (Gaussian beam profile). T he damage threshold was defined as the energy density, EDth, that prod uced minimal superficial epithelial lesions. Thresholds have been dete rmined for sequences of 2, 8, 32, 128, and 1024 pulses at a rate of 10 Hz. The damage data are shown to be correlated by empirical laws rela ting either the threshold energy density per pulse to the number of pu lses, or the total threshold energy density to the duration of the pul se train. Research is underway to obtain data for pulse sequences at g reater pulse rates and to examine the relative importance of thermal a nd acoustic damage mechanisms. (C) 1998 Laser Institute of America.