The NIKE electron beam-pumped KrF amplifiers

The NIKE laser at the Naval Research Laboratory is an angularly multiplexed KrF laser system designed to study the physics of direct drive laser fusion. NIKE will produce 3 kJ of 248 nm light in a 4 nsec pulse. The two final amplifiers are both electron beam pumped systems. The smaller of the two amplifiers, which has a 20 cm × 20 cm aperture, is fully integrated into NIKE. Faraday Cups, pressure jump diagnostics, and dosimetry media have verified that the energy deposition and pumping uniformity meet the NIKE requirements. Using the observed deposition, we have employed our own models to accurately predict the observed gain of the input laser pulse. The larger amplifier has a 60 cm × 60 cm aperture and is pumped by two independent electron beam generators, with each side capable of producing a 670 kV, 500 kA, 290 nsec flat top electron beam. The electron beam from one side has deposited between 30 and 45 kJ into the gas. Our calculations show that the combined deposition from both sides should be sufficient to produce the required 5 kJ laser output, with 3 kJ reaching the target. Faraday Cup measurements show the current injected into the cell across the 200 cm × 60 cm cathode to vary by less than 10%. In both amplifiers the transmission efficiency from cathode to laser cell is around 50%.