Raman pulse compression of excimer lasers for application to laser fusion

Application of efficient ultraviolet excimer lasers such as the 248 nm KrF laser to laser fusion requires that long laser pulses be efficiently converted to short pulses at high intensity. The backward Raman amplifier is shown to be a promising candidate for this application. Gain, saturation, and limits to amplifier performance are described. It is shown that pump beams of poor spatial quality may be converted to output beams of high spatial quality. Several common gaseous vibrational Raman scatterers are discussed, and it is shown that a simple KrF-pumped backward Raman amplifier using methane at atmospheric pressure will have a saturation fluence near 1 J/cm²and can produce an output five times as intense as the pump in a ten times shorter pulse with an efficiency of about 50 percent. Design tradeoffs and possible techniques for further improving the performance of such amplifiers are discussed.