Pulsed DF laser effects

Laser effects caused by pulsed DF laser beams have been investigated under one-dimensional plasma conditions. The high energy pulse from a 50-liter photoinitiated chemical laser was utilized to measure both metal and fiberglass target responses to incident fluences up to 150 J/sq cm. In thermal coupling experiments with aluminum, the absorbed fluence showed enhancement just above the plasma threshold, reaching 5 J/sq cm at an incidence fluence of 31 J/sq cm. Plasma ignition time shortened with incident fluence. Other coupling phenomena, in particular heating, were also dependent on ambient pressure for aluminum, titanium, and other metal targets. A novel multiple pulse effect was discovered: experiments with repeated pulses on targets of aluminum alloy showed increasing damage and thermal coupling with the number of pulses. Up to 14 J/sq cm were absorbed at 65 J/sq cm incident fluence. The absorptance at low intensities was also found to be greatly increased by such a series of pulses which produced plasma.