(Received April 21, 1966)
The degree of the decrease in the population of ground-state Cr ions in ruby brought about by optical pumping with Xe flash light has been measured as a function of time under Q-switching operation. The measurement has been made by observing the decrease in absorbing power of the ruby crystal for a probe light (Hg 5461Å), (γ), while Q-switching with a rotating prism or saturable absorber (Cryptocyanine). Observations of rapid change of (γ) due to the emission of giant pulse laser light have been carried out, with the very satisfactory results. At the occurrence of a giant pulse, the higher the initial value of (γ) is, the lower becomes the final value of (γ).