Study on Nd:YAG rods double-pass amplifying side-pumped by diode laser arrays

A diode laser pumped Q-switched double-pass MOPA system operated on 400 Hz repetition rate and 15 ns pulse width has been investigated in this paper. The laser with a beam expanded mirror and a beam isolated equipment is amplified by two 6.5 kW diode laser pumped modules, each has 81 diode lasers. Two modules pumping Nd:YAG rod is used. Compensation of thermal birefringence is achieved by inserting a 90°crystal quartz rotator and using an imaging optical system between the two module. Besides, two appropriate concave lenses are placed on both sides of each pumped module for thermal lensing compensation. Accordingly, approximate apparel beam can be obtained through laser rods. The laser system developed can output 400 mJ energ with an optical-optical efficiency of 12.3% and beam quality of