Characteristics of an x-ray preionized TEA CO laser

Abstract

Abstract.A cryogenically cooled sealed-off x-ray preionized self-sustained discharge CO laser was succesfully operated. It was found that 20 to 40 % higher output energies could be obtained using x-ray instead of uv preionization. A maximum output energy of 2.9 J per pulse could be extracted from a 2 x 2 x 40 cm 3 discharge volume. The maximum electrical efficiency proved to be 12.6 %. PACS: 42.55 EIt is well known that efficient high energy pulsed CO lasers can be built exploiting electron beam-sustained discharge techniques. The efficiency of these lasers is superior to that of similar CO2 lasers. Already in 1974 Mann et al. [1] reported output energies of 150 J per pulse obtained from a 21 discharge volume with an electrical efficiency of 63 %. 1600 J output pulses were reported by Boness and Center [-2] in 1977, extracted from a 161 discharge volume with an electrical efficiency of about 40 %.However, the construction of an efficient selfsustained discharge CO laser appeared to be much more difficult, especially for large apertures. The first self-sustained laser was reported in 1974 by Cohn [3] who extracted 200 mJ pulses from a 2.5 x 5 x 50 cm 3 discharge with an electrical efficiency of 1.8 %. In 1978 Schmid [4] obtained 5 J pulses from a 5 x 5 x 50 cm 3 discharge with an electrical efficiency of 2 %. Higher efficiencies were for the first time reported by Peters [-5] in 1978. He obtained 625mj pulses from a 1 x I x 60 cm 3 discharge with an electrical efficiency of 15.6%. In 1981 Peters [6] reported the same energy from a 1 x I x 18 cm 3 discharge with an electrical efficiency of 12.1%.An important characteristic of a self-sustained discharge is the need of a certain amount of homogeneous preionization [7]. Commonly uv photons are used to achieve this preionization.However, uv photons have severe limitations as a preionization source. Due to absorption and to their low energy they have a short range and are mainly acting upon heavy atoms and molecules such as Xe and organic impurities present in the gas mixture or upon the electrodes resulting in an inhomogeneous preionization. So in general obtaining sufficient homogeneous preionization will become more difficult using larger apertures and higher gas pressures. Moreover, in the case of CO heavy atoms and molecules are frozen out of the lasergas because for efficient operation the lasergas has to be cooled down to cryogenic temperatures.In the present paper the performances of a selfsustained discharge CO laser, using x-ray preionization, will be discussed. Earlier this preionization technique proved to be superior in the case of and high pressure CO2-1asers [9] but up to now no experiments with CO have been reported.2.8 J output pulses were extracted from a 2 x 2 x 40 cm 3 discharge volume with an electrical efficiency of 10%. Because the system could also be operated with a corona type uv preionization scheme it was possible to study the difference in performance between the uv and the x-ray preionized system. It was found that 20-40% higher outpu...