The results of measurements of the spatial and temporal dependence of the gain of a pulsed SF6-H2hydrogen fluoride laser are reported and are compared with those for CO2lasers. While the propagation in space of a locally excited gain medium was observed to be comparable for two lasers, the time developments were vastly different. The spatial dependence of the gain for each of these lasers was measured by probing a pin laser amplifier with a small oscillator beam, while varying the distance of the probe beam from the plane of the amplifier discharge. The spatial FWHM of the gain for both HF and CO2was typically observed to be 6 mm, considerably larger than the visible glow region. Using delay techniques, the oscillator-amplifier configuration was also employed to study the gain of these lasers as a function of time. While the CO2gain typically decays after tens of microseconds, the HF gain typically does so after 1 to 2 μs. In addition, by varying the formation rate of HF, it was shown that HF itself is most likely the principal agent of this very rapid gain relaxation. This is a severe basic limitation to the efficient power output of all CW and long-pulse HF lasers. Short pulse HF devices, however, can be operated at relatively high energy. We have demonstrated this by obtaining 350-mJ pulses from a 75-cm pin laser using a 50-ns excitation pulse from a Marx bank.