Measurements of Beam Divergence of Q-Switched Ruby Laser Rods

A method of measuring beam divergence is reported that provides simultaneous variable intensity multiple exposures of the laser output on Polaroid film, and does not require densitometer tracings of the exposures to establish the beam divergence. Using this technique, beam divergence as a function of power output of 12 ``Q-switched'' ruby rods is reported. Inference is made that the active divergence of a ruby rod is the sum of the passive beam divergence of that rod plus the divergence due to radial mode structure. Thermal distortion probably contributes very little to the beam divergence.