Near Infrared Lasing Transitions in Ar, Kr, and Xe Atoms Pumped by a Coaxial e-Beam

Optimizations of gas composition and input energy were performed for gas mixtures containing a buffer gas and either Ar, Kr or Xe as the lasing gas. The total gas pressure was varied between 1 and 14 bar and the input energy from 0.03 to 0.7 J/cm 3. The excitation source was a small coaxial electron beam with a pumping length of 20 cm and a pulse length of 30 ns (FWHM). From an active volume of 13.3 cm 3 a maximum output energy of 12 mJ was obtained from a gas mixture containing 0.3% Xe in Ar at a total gas pressure of 10 bar. The intrinsic efficiency was 0.9%. PACS: 42.55 FN, 41.80 Dd Atomic rare gas lasers have been known from the very beginning of laser physics. It was shown in 1963 that a high gain is possible in a tube filled with Xe at a low pressure [1]. A decade later the pulsed atomic rare gas lasers gained attention again as it was shown that they could work at atmospheric pressures as well [2-4]. Recently Basov et al. [-5] reported a total efficiency of over 3% for an Ar:Xe laser pumped by a long pulse e-beam sustained system at a total gas pressure of 3.5 bar. In this paper we will report on optimization experiments with respect to the gas composition and pumping conditions at a high total gas pressure. The gas pressure could be varied between 1 and 14 bar. Each gas mixture contained a low content of either Ar, Kr, and Xe as the lasing gas diluted in either Ar, Ne or He as a buffer gas. To our knowledge only Chapovsky et al. [4] worked at such a high pressure but in a capacitively coupled discharge system. Our results are, however, an order of magnitude better. 1. Experimental Configuration The laser gas was excited by a small coaxial electron beam apparatus [6]. The maximum diode voltage was about 300 kV with a peak diode current of 7.5 kA in a pulse with a length of 30 ns (FWHM). * Present address: Institute of Electronics, Academia Sinica, Beijing, People's Republic of China The anode tube with a wall thickness of either 25 or 50 gm is made out of titanium. The inner diameter is 9.2 mm and the laser gas inside the tube is irradiated by the electrons over a length of 20 cm resulting in an active volume of 13.3 cm 3. The length of the resonator was 400 mm and it consisted of a gold coated total reflector with a radius of curvature of 2 m on one side, and a partial reflecting mirror on the other side. The output energy was measured with a Laser Precision RJP 734, 735 RJ 7000 combination. The spectral composition was studied by means of a Hilger & Watts monochromator with a focal length of 30 cm and equipped with a 150 1/mm grating blazed at 4 gin. The outcoming signal was detected by a uncooled InSb (ORP-10) detector. 2. Experimental Results 2.1. Ar :Xe Gas Mixture In order to estimate the intrinsic efficiency (which is defined as the ratio of the output laser energy and the input energy deposited in the gas) the energy deposition was measured by the pressure-jump method. This method was described already in an earlier paper [6]. In that paper the results are presented for the energy deposition in the gas for the case where a titanium tube with a wall thickness of 50 ~m is used as anode. In Fig. 1 the results are plotted for a total gas pressure up to 10 bar. All numbers in the figure are 188 P . J . M . Peters et al.