Visible Lesion Thresholds with Pulse Duration, Spot Size Dependency, and Model Predictions for 1.54-mum Near-Infrared Laser Pulses Penetrating Porcine Skin

摘要

Er:glass lasers have been in operation with both long pulses (hundreds of microseconds) and Q-switched pulses (50 to 100 ns) for more than 35 yr. The ocular hazards of this laser were reported early, and it was determined that damage to the eye from the 1.54-microns wavelength occurred mainly in the cornea where light from this wavelength is highly absorbed. Research on skin hazards has been reported only in the past few years because of limited pulse energies from these lasers. Currently, however, with pulse energies in the hundreds of joules, these lasers may be hazardous to the skin in addition to being eye hazards. We report our minimum visible lesion (MVL) threshold measurements for two different pulse durations and three different spot sizes for the 1.54-microns wavelength using porcine skin as an in vivo model. We also compare our measurements to results from our model, based on the heat transfer equation and the rate process equation. Our MVL-ED50 thresholds for the long pulse (600 microsecs) at 24 h postexposure were measured to be 20, 8.1, and 7.4 J cm2 for spot diameters of 0.7, 1.0, and 5 mm, respectively. Q- switched laser pulses of 31 ns had lower ED50 (estimated dose for a 50% probability of laser-induced damage) thresholds of 6.1 J cm(2) for a 5-mm-diam, top-hat spatial profile laser pulse.