Fast rise pulses from a GaAs electrooptic switch are used to measure the small signal time response to a step of radiation, of a 20 dB, homogeneously broadened CO2, He, N2laser amplifier. By comparing the observed shape of the time response (rise time ≈ 15 nsec) with theory, the value ofT2, the homogeneous relaxation time, and hence the linewidth is obtained as a function of gas pressure. The doppler broadening (59 MHz), pressure broadening (4.67 MHz/Torr) and gas temperature (372°K) are obtained.