Laser action at 172.9 nm has been observed in xenon and krypton-xenon mixtures following short-pulse excitation (2.5 nsec) by a relativistic electron beam. Peak powers [inverted lazy s] 80 kW cm-2 in a 5-nsec pulse were obtained. The pumping sheme used in this work is noteworthy because its high efficiency has made it possible to utilize a simple compact electron accelerator (total electron beam energy 6 J) for excitation. The present short-pulse data suggest that the rapid decrease in energy efficiency of this laser at high xenon pressures may be due to excited-state quenching by ground-state xenon atoms. © 1973 American Institute of Physics.