Development Of LD-pumped Nd:YAG Laser MOPA System

Abstract

An inertial confinement fusion (TCF) power plant will require a driver having specifications such as a 10-MJ blue output,a IO-Hz repetition rate and an overall efficiency of 10%. Laser diode (LD)-pumped solid-state lasers have been proposed as one of feasible candidat? drivers satisfying these requirements lv2. A small scale experiment of a LD-pumped Nd:YAG laser MOPA(Master Oscillator Power Amplifier) system with a harmonic generator is now in progress to show partly the feasibility for an ICF reactor driver3. The 1.064-pm 1-ns pulsed output energy will be -8OmJ at 50Hz. This MOPA system is composed of (a) an A0 mode locked Qswitched oscillator with a concave reflector to compensate the thermal lensing effect, (b) a regenerative amplifier pumped by two 300-W quasi-cw LD arrays,and (c) a main amplifier having five Nd:YAG disks pumped by ten 300-W quasi-cw LD arrays. These disks are cooled by helium gas flowing. The main technical issues to be experimentally investigated are (1) excitation efficiency for LD array pumping, (2) extraction efficiency of regenerative and main amplifiers, (3) surface cooling techniques of disks using helium gas flowing, (4) frequency conversion efficiency at high repetition rate, and (5) thermally induced lens and birefringence effects and their compensation. The operating characteris tics and performance characteristics of the LDpumped MOPA system are presented.