High power optically pumped far infrared laser systems

Abstract

Single mode, 60-80 ns pulse width, 50-70 kW peak power laser oscillators operating on the 384.6 pm line of DzO have been developed. The characteristic linewidths of these oscillators are less than 25 MHz full width at half maximum which favorably compares with the intrinsic width of 6-8 MHz associated with the pulse length of about 6 0 ns. A 12.7 mJ, 195 kW, 384.6 pm D2O laser oscillatoramplifier combination has been constructed and tested. Although single longitudinal mode operation is attained from this oscillatoramplifier system, amplified spontaneous emission (superradiance) from the amplifier adds low power level wide-bandwidth background radiation. Studies of far infrared lasing action in CH3F and CH31 are also described. T HE potential application of high power narrow linewidth far infrared radiation (FIR) for determination of ion temperature in tokamak plasmas by Thomson scattering was proposed [ l ] , [2] after the first demonstration of optically pumped laser action in CH3F [3] and the subsequent production of higher power outputs from mirrorless lasers [4], [5]. At present it appears that power levels on the order of 1 MW, pulse energies on the order of 200 mJ, and full linewidth of 20-40 MHz between 10 dB points are required. Also full widths of less than 100 MHz at the 30 dB and 200 MHz at the 50 dB points are required for Thomson scattering measurements of tokamak plasmas and other hot plasmas with electron densities of about 1014 ~m-~. In this paper we discuss various means of achieving high power, narrow linewidth output from a FIR laser system. Attempts have been made to generate high power narrow linewidth radiation in CH3F by pumping it with the 9.55 pm P(20) line of high power pulsed C02 lasers. Reasonably good power conversion efficiencies were obtained in amplified spontaneous emission (ASE) type lasers [6]-[ 101. A variety of linewidths were reported for these lasers, all of them in the