KrF Laser Amplification in the Multi-Staged Electra Facility

Summary form only given. Electra is a rep-rated, e-beam pumped KrF laser system at the Naval Research Laboratory investigating the physics and technology required for inertial fusion energy. To date the main cell (30times30 cm² aperture) has operated as an oscillator and achieved ~1.5 kW at 5 Hz for 2000 shots. It has also performed continuously at 2.5 Hz for over 22,000 shots. The next step is to convert Electra into an amplifier system. The planned design has three components. A commercial KrF discharge oscillator (1.3times3 cm² aperture, ~1 J output) will provide the initiating laser pulse. This pulse is then sequentially amplified through a preamp (10times10 cm² aperture) in a single pass, followed by a double pass through the main amp. The final system output laser energy depends upon the e-beam pumping power in each amp, which in turn depends on the particular cathode and hibachi configurations. To examine this dependency the KrF kinetics/laser simulation code Orestes has been used to follow the growth of the low energy oscillator pulse as it sequentially propagates through the two amplifiers. Initial calculations predict final output energies of ~200 J for monolithic (uniform emitting) cathodes and ~700 J for stripped cathodes designed for maximum gas deposition efficiency. In addition to the energy, the final output laser pulse shape is a complex product of the amplification and timing between the multiplexed laser pulses and the e-beam pulsed power. Simulations for the preamp have demonstrated partial agreement with the profiles and provide a test of the molecular/plasma kinetic processes used in Orestes.