Oscillation at 172 nm for 200 nsec has been observed at a pressure of 1.5 atm of xenon with a 1‐m length of gain medium pumped by a 200‐kV 7‐A/cm21‐&mgr;sec electron beam. The observed behavior agrees with calculations based on the excited‐state mixing model for this new operating regime. The results support model predictions that a modest increase in excitation rate (about a factor of 2) would yield quasi‐steady‐state laser oscillation with an intrinsic efficiency near 5%, a fluence of ∼1 J/cm2, and a peak intracavity two‐way flux of ∼50 MW/cm2. In optimized laser amplifier designs, significantly higher amplifier efficiencies should be possible.