LASER PROPULSION USING FREE-ELECTRON LASERS

Quasisteady plasmas have been initiated and sustained in argon at pressures from one to three atmospheres using power absorbed from a 10.6-mum wavelength laser beam produced by the RF linac free electron laser at Los Alamos National Laboratory. The pulse format of the RF linac laser consisted of an 80-mus-long burst of 10 ps pulses separated by 46 ns, with an average power of approximately 3.75 kW. Time-resolved spectroscopic observations revealed no decay of the plasma during the 46 ns interpulse time. Analysis of the spectroscopic data using Boltzmann factors, ion-neutral intensity ratios, and absolute emission coefficients gave values of the plasma temperature that varied from 17,500 K to 20,000 K during the 80-mus pulse. Attempts to obtain optical breakdown in nitrogen and hydrogen proved unsuccessful, even at optical intensities ten times the observed threshold for argon.