BEAM QUALITY AND EFFICIENCY OF HIGH-AVERAGE-POWER MULTIROD LASERS

Multirod lasers in a resonator/amplifier configuration were investigated with respect to beam quality, efficiency and upper limit of the output power. Using a lensline-like set-up, the output power can be increased proportional to the number of rods, without affecting the beam quality. The instabilities of the lens line and the requirements for alignment were examined theoretically and experimentally. The beam parameter product-theta-d/4 depends on the length of the resonator and on the desired output power variation. Values of theta-d/4 = 42 mrad mm at 1.9 kW output power were obtained with a resonator, total length 2.25 m, comprising six Nd:YAG rods of phi-8 mm X 152 mm. Lower beam parameter products are possible, but with reduced efficiency. Such a lensline resonator/amplifier system can be scaled up easily. An upper limit of the output power is given by the internal losses and can be estimated to be approximately 10 kW.