High pressure Xe and Ar were excited by high-current relativistic-electron bursts. The spectral and temporal characteristics of the uv continua, centered near 1700 A. in Xe and 1260 A in Ar, were measured. The maximum of the Xe spectral distribution shifted from 1690+ 9 to 1710+9 A. , and the spectral width decreased from 150+ 3 to 110+3 A. when the pressure was raised from 2 to 34 atm. The shift of the Ar continuum centered at 1260+ 9 A was negligible and the spectral width decreased from 130+ 3 to 90+ 3 A when the pressure was raised from 2 to 61 atm. Exponential time constants for the buildup and decay of the Xe and Ar continua were obtained. They are characterized by aP t 5 pressure dependence below 3 atm. Pressure-independent decay time constants of 4+ 1, 16+ 2.5, and about 280 nsec were obtained for Xe at high pressure. For Ar the pressure-independent decay time constants were 6+ 1.5, 30+ 5, and about 230 nsec. The efficiency for conversion of electron kinetic energy to uv energy was 10+ 4% in Xe and 15+ 7% in Ar.

Vacuum ultraviolet (VUV) emission characteristics of xenon for pressures from 15 to 450 psi are presented. Stimulated emission was observed above 200 psi. Experiments were run both with and without mirrors. Without mirrors, the emission was 150 Å wide centered at 1700 Å, and the mean radiative lifetime was 2×10−8. The energy conversion efficiency was ∼ 20%. With mirrors above 200 psi the emission width narrowed to 17 Å centered at 1716 Å, and the output was highly directional. The pulse width narrowed from 50 to ∼ 3 nsec.

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