Some effects connected with multiple passes of pump radiation in laser pump cavities are discussed. These effects include changes in mercury arc lamp operating characteristics, when the lamps are used inside the cavities as pump sources, and unexpectedly low pulse (but not cw) thresholds in double elliptical cavities. It is shown analytically that these effects can, at least in part, be attributed to the shapes of the pump light energy distribution curves after multiple passes through the pump cavities, and to the relative opacities of flash and continuous lamps.
V. Evtuhov and J. K. Neeland, "Multiple Pass Effects in High Efficiency Laser Pumping Cavities," Appl. Opt. 6, 437-441 (1967)