STRONG TL-XE EXCIMER BAND EMISSION VIA ELECTRON-BEAM INITIATED DISCHARGES IN TLI AND XE MIXTURES

Stable glow discharges have been produced by an electron beam ionizing pulse (20 nsec) in TlI/Xe mixtures having densities of approximately 1-4×1016/cm3 of TlI and 1019-10 20/cm3 of Xe in order to assess their potential as a medium for a high power Tl-Xe excimer laser system. The use of this thallium salt in place of the pure Tl metal enabled the required operating temperature to be lowered from 820 to 440°C. These e-beam initiated discharges are the first type conducted in metal vapors at these high operating temperatures. The electron beam preionized discharges (60 cm3) produced a factor of 40 enhancement in the Tl-Xe band emission relative to the pure electron beam pumping. Peak power loadings of 3 kW/cm3 were attained for approximately 600 nsec at 2 A/cm2 current densitites for E/N values up to 3×10-17 V cm2. Higher peak power loadings (31 kW/cm3) were achieved for shorter pulsewidths without the onset of glow-to-arc transitions. Very strong emission was observed from only the Tl atomic lines and the Tl-Xe bands centered at approximately 6000, 4300, and 3650 Å. No emission from excited TlI was ever observed. Monitoring the discharge current gave a TlI attachment rate constant of 1.8×10 -10 cm3sec-1 that was very insensitive to the applied E/N. Available kinetic information is used to develop a plausible model for the dominant kinetic processes involved. The possibility of utilizing the close energy resonance of the Tl and I metastable states to produce lasing at 1.315μ is discussed. In addition, engineering details of the test cell construction compatible with the required high operating temperatures are presented.