Interactions of intense ultraviolet laser radiation with solid aerosols

Abstract

Characterizations of the interaction of intense ultraviolet laser radiation (λ=248 nm) with small solid aerosols are presented. Interaction dynamics, velocity measurements of expelled material, and thresholds for plasma formation are presented for aluminum, calcium fluoride, glass, silicon carbide, and tungsten particles. An excimer laser operating with a krypton fluoride gas mixture was used to irradiate small solid aerosol particles (≊5–50 μm) under atmospheric and vacuum conditions down to 10−5 Torr. Focused laser radiation intensities varied from 107 W/cm2 to a maximum of 2×1011 W/cm2. Interactions of the laser radiation with the solid aerosols were recorded in real time by an ultraviolet laser imaging system. Velocities between 250 and 2000 m/s were measured for material ejected from particles undergoing laser interaction. Laser intensity thresholds for visible plasma emission ranged from a maximum of 650 MW/cm2 for aluminum to a minimum of 59 MW/cm2 for tungsten. Thresholds for plasma formation were determined to be relatively independent of ambient pressure.