Skin tissue optical and thermal reactions to pulse sequences of thulium yttrium aluminum garnet laser irradiation

Abstract

The increasing interest in new lasers operating in the mid-infrared region has produced a need for better understanding of tissue reactions for safety purposes. One of the lasers of interest for skin irradiation is the Tm:YAG which produces 2.0 micron wavelength light. However, there are many vital pieces of knowledge missing to calculate thermal effects of two micron light interactions with human skin. This work aims to fill several of these deficiencies. The first unresolved issue is the fundamental optical absorption coefficient of skin layers for 2.0 pm because current published values span two orders of magnitude. A new method for measuring optical absorption rates which avoids most of the factors introducing uncertainties in current approaches is therefore presented. The second issue unaddressed in literature is the effect of delivering the laser energy in multiple pulses which nullifies the normal assumption of thermal confinement. The third issue that published literature leaves confused is the values of thermal constants used in heat modeling. The wide ranging values of these constants is shown to allow models to drastically differ from measured temperatures. The final issue to be resolved for the first time is the effective depth of measurement of thermal imaging non-contact temperature measurement instruments.