Optimized diode-pumped Nd:glass prototype regenerative amplifier for the National Ignition Facility (NIF)

The National Ignition Facility (NIF) will house a 2 MJ Nd:glass laser system to be used for a broad range of inertial confinement fusion experiments. This record high energy laser output will be initiated by a single low energy, fiber-based master oscillator which will be appropriately shaped in time and frequency prior to being split into 48 beams for intermediate amplification. These 48 intermediate energy beams will feed the 192 main amplifier chains. We report on the baseline design and test results for an amplifier subsystem in the intermediate amplifiers. The subsystem is based on a diode pumped, Nd:glass regenerative amplifier. The amplifier is comprised of a linear, folded, TEM00, 4.5 m long cavity and represents the highest gain (approximately 107) component in the NIF laser system. Two fundamentally important requirements for this amplifier include output energy of 20 mJ with a square pulse distortion of less than 1.45. With a single 48 bar 4.5 kW peak power diode array and lens duct assembly, we pump a 5 mm diameter X 50 mm long Nd-doped, phosphate glass rod, and amplify the mode-matched, temporally shaped (approximately 20 ns in duration) oscillator seed pulse to 25 mJ of output energy with a very acceptable square pulse distortion of 1.44. This most recent design of the regenerative amplifier has increased the performance and reduced the cost, enabling it to become a solid baseline design for the NIF laser system.