[en] The expanded beam of a Q-switched single mode ruby laser is used in a double exposure holographic interferometric arrangement to study the optical homogeneity of a discharge in a 1 : 1 : 8 mixture of CO2, N2, and He at 600 torr. An acoustical wave is seen to propagate from the cathode, but it is shown that for the first 4 to 7 μ sec, there is good optical quality in the central region of the laser medium. (U.S.)