Prepulse elimination in high-power CO2 lasers

We are presently completing a CO2 laser designed to produce peak power in excess of 2 TW to study the scaling characteristics of pellets for laser induced fusion. The design goal of 2500 J in a 1 nsec pulse also includes other requirements, among them being that the energy on the target before the arrival of the main pulse be kept under 100 μJ. This requirement is needed to prevent the target from disintegrating before the TW pulse can compress it. Since the small signal gain in the dual-beam triple-pass amplifier is estimated to be about 108, the prepulse energy from the oscillator–preamplifier feeding the final amplifier must be less than 10−12 J. Since about 0.2 J is required to drive each half of the dual beam module, a prepulse rejection ratio better than 4 × 1011 must be achieved.