New Infrared Laser Lines in Argon, Krypton, and Xenon

Fourteen new infrared laser transitions in Ar, Kr, and Xe ranging from 3.725 to 17.233 pm are reported. All of the Kr laser transitions and all but oneof the Ar and Xe transitions have upper levels in the s or d state: the majority of the transitions satisfy the condition AK = AJ. Identification of a previously observed, unidentified laser line at 5.804 pm in AI is given. Nobel gas lasers are of interest for many applications because they exhibit long-term frequency stability, a wide range of wavelengths, and useful power levels. In pulsed systems high peak power has been observed over a wide range of wavelengths [ 11, [ 2 ] , [ 6 ]. Because of the interest in new infrared (IR) lasers and the lack of published data in the IR under these conditions, a survey of Ar, Kr, and Xe was conducted. A 3 m longitudinal discharge laser capable of operation at pressures down to 5 p and at current densities up to approximately 175 A/cm2 was used. Nineteen new transitions were observed, ranging in wavelength from 3.631 to 17.233 p. All but one of the transitions were identified as neutral species, although it had been anticipated that new transitions at high current densities would be ionized species. The strongest transitions were observed in Kr at 4.15 p and Xe at 7.8 and 8.4 p. A longitudinal discharge laser was used for this work [ 21. The plasma tube was made from Pyrex tubing with an inside diameter of 19 mm and the electrical discharge was divided into two 1.5 m sections for better stability. Each end of the laser contained an indium cathode [3] and the center electrodes were grounded anodes constructed from molybdenum. The ends of the plasma tube were sealed with KC1 Brewster windows which passed radiation with wavelengths from 0.1 to 17 pm, although the optical quality of the windows hindered oscillation at wavelengths below roughly 1 pm. The optical cavity consisted of a 20 m radius mirror and a flat containing a 3 mm diameter pinhole to couple out radiation. Both mirror surfaces were silver overcoated with thorium oxyfluoride. 0.2 pF capacitors were charged to a voltage of 16-20 kV and discharged through the plasma tube with a spark gap. The current rise time was roughly 1 ps, and peak current densities up to 176 A/cm2 were obtained. Rough wavelength measurements …