Evaluation of the effect of prepulses on HF laser-target interactions

Abstract

We have assessed the effect of multinanosecond, low-power-density prepulses on the interaction of multinanosecond, 10/sup 14/ W/cm/sup 2/, approx. 3 -..mu..m HF laser pulses with slab targets. The emphasis is on analyzing absorption and x-ray conversion efficiency. A survey of previous experiments gives no evidence that these prepulses will affect the total absorption. However, prepulses have been observed to cause qualitative changes in both the x-ray spectrum and conversion efficiency. Numerical simulations indicate that the laser-target interaction is effectively insensitive to low-power-density prepulses. These studies imply that basic laser-target experiments with multiplexed, HF laser pulses will provide an important characterization of the interaction of long pulse, multi-line, approx. 3 ..mu..m radiation with targets. Future wavelength comparison experiments will require prepulse suppression or target isolation.