Infrared skin damage thresholds from 1319-nm continuous-wave laser exposures

Jeffrey W Oliver,Kurt J Schuster,Gavin D Buffington,Robert J Thomas,David J Stolarski,Clifton D Clark,Gary D Noojin,Aurora D Shingledecker,Justin Maughan,Rebecca Vincelette,Semih S Kumru,Naomi Kitzis,Corey A Harbert

doi:10.1117/1.jbo.18.12.125002

Abstract

A series of experiments were conducted in vivo using Yucatan miniature pigs (Sus scrofa domestica) to determine thermal damage thresholds to the skin from 1319-nm continuous-wave Nd:YAG laser irradiation. Experiments employed exposure durations of 0.25, 1.0, 2.5, and 10 s and beam diameters of ∼0.6 and 1 cm. Thermal imagery data provided a time-dependent surface temperature response from the laser. A damage endpoint of fifty percent probability of a minimally visible effect was used to determine threshold for damage at 1 and 24 h postexposure. Predicted thermal response and damage thresholds are compared with a numerical model of optical-thermal interaction. Resultant trends with respect to exposure duration and beam diameter are compared with current standardized exposure limits for laser safety. Mathematical modeling agreed well with experimental data, predicting that though laser safety standards are sufficient for exposures <10 s, they may become less safe for very long exposures.

Highlights

Standards committees are currently pursuing revisions of laser safety exposure limits to the eye
Laser-damage thresholds of the skin are considered to be much greater than those of the eye in the retinal hazard region of 400 to 1400 nm. This may not be true in some regions of the spectrum where the absorption length within the eye is on the order of a centimeter, and the laser has a transmittance to the retina resulting in an irradiance level that can be similar to the levels at the cornea
Lesions resulting from exposures at or near the ED50 generally appeared as a small pink spot ∼1.5 mm in diameter at the 24-h observational endpoint, regardless of exposure duration or laser-beam diameter

Summary

Introduction

Standards committees are currently pursuing revisions of laser safety exposure limits to the eye Some of these revisions are focused on the near-infrared region and are based primarily upon new data collected within the wavelength region of 1100 to 1400 nm.[1] Near the wavelength of 1300 nm, these exposure limits are anticipated to be increased by the largest margin relative to the values established in the year 2000. Laser-damage thresholds of the skin are considered to be much greater than those of the eye in the retinal hazard region of 400 to 1400 nm This may not be true in some regions of the spectrum where the absorption length within the eye is on the order of a centimeter, and the laser (while focused at the retina) has a transmittance to the retina resulting in an irradiance level (when considering the beam diameter at and energy transmitted to the retina) that can be similar to the levels at the cornea. This yields a spectral region of some of the highest measured thresholds for laser damage to tissues.[2,3] As a skin exposure includes tissues with much larger scattering coefficients along with pigmentation absorption, it is hypothesized that the damage threshold may be lower within the skin than within the cornea and

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