Cooperative phenomena in two-pulse two-color laser photocoagulation of cutaneous blood vessels

Abstract

A novel laser system has been developed to study the effects of multiple laser pulses of differing wavelengths on cutaneous blood vessels in vivo, using the hamster dorsal skin flap preparation. The system permits sequenced irradiation with well-defined intrapulse spacing at 532 nm, using a long pulse frequency doubled Nd:YAG laser, and at 1064 nm, using a long pulse Nd:YAG laser. Using this system, we have identified a parameter space where two pulses of different wavelengths act in a synergistic manner to effect permanent vessel damage at radiant exposures where the two pulses individually have little or no effect. Using a two-color pump-probe technique in vitro, we have identified a phenomenon we call green-light-induced infrared absorption (GLIIRA), where a pulse of green light causes photochemical and photothermal modifications to the chemical constituents of blood and results in enhanced infrared absorption. We identify a new chemical species, met-hemoglobin, not normally present in healthy human blood but formed during laser photocoagulation which we believe is implicated in the enhanced IR absorption.

Optical properties of selected native and coagulated human brain tissues in vitro in the visible and near infrared spectral range

“…absorption and scattering). It is probably worth noting that a similar increase of both absorption (by a factor of 2-10) and scattering (by a factor of 2-4) coefficients in the wavelength range from 500 nm to 1100 nm was recently reported for coagulated human blood by Black et al (2001). Published data on the optical properties of white and grey brain matter are rare.…”