Plasma-formation threshold conditions for the interaction of pulsed ultraviolet radiation with solid targets

An experimental investigation was made of the factors influencing the threshold laser intensity I* for the formation of a plasma when series of radiation pulses of wavelength 308 nm and overall duration 30 nsec interacted with solid targets. Two mechanisms influencing I* were established: laser cleaning, which increased I*, and stimulated rearrangement of the illuminated surface zone by periodic laser action, which lowered I*. It was found that by recording certain optical characteristics of the region where the laser radiation interacted with the target one could provide a criterion for stabilizing I*.