George Frangineas

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 and in vitro, using cuvettes of whole or diluted blood. 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, 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 near-infrared absorption.

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

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.

Design and performance of a high-power modelocked Nd:YLF laser

The design and performance characteristics of a TEM(00) mode Nd:YLF laser oscillator which can produce over 35 watts CW at 1053 nm are described. Performance data for Q-switched operation and for mode-locked operation are also presented. The performance of the laser was analyzed using a plane-wave extraction model, and the results are presented.

Review of cw high-power diode-pumped green lasers

Recent progress in pump sources and basic materials have allowed the production of commercially viable, high-power, diode-pumped, continuous-wave, green lasers. We will review the history and the technological developments that have allowed this progress.

Materials for high-power second-harmonic generation

The frequency doubling of laser radiation at 1064 nm is studied in order to characterize efficient harmonic materials capable of delivering second-harmonic average power at the multiwatt level. Three nonlinear materials are considered: Mg:LiNbO3, potassium titanyl phosphate (KTP), and lithium triborate (LBO). No photoreactive damage is observed in Mg:LiNbO3; however, it exhibits broadening of the temperature tuning curves and distortion of the harmonic beam. An average output power in excess of three watts is extracted from KTP, but the material shows optically induced nonuniformities in the n(z) refractive index. LBO as a harmonic converter achieves 2.2 W at 532 nm, though the fundamental beam has to be tightly focused in the crystal.