Electra : repetitively pulsed 700 J, 100 ns electron beam pumped KrF laser

Electra is a repetitively pulsed, electron beam pumped Krypton Fluoride (KrF) laser at the Naval Research Laboratory that is developing technologies to meet the Inertial Fusion Energy (IFE) requirements for durability, efficiency, and cost. Electra has demonstrated single shot and rep-rate laser energies as an oscillator exceeding 700 J with 100 ns pulsewidth at 248 nm. Peak output of 731 J laser energy in single shot operation demonstrates a total pulse intrinsic efficiency of 8.3%, and an intrinsic efficiency during the flat-top region of 9.6%. Improvements in the window transmissivity from the present 93% to excimer grade fused silica with anti-reflection coatings on both sides could provide up to 17% enhancement of the output intensity, and likewise for the efficiency. The Electra KrF gain measured in 4 positions of the laser aperture in an amplifier configuration demonstrates near field uniformity. In addition, the amplifier and oscillator results are qualitatively consistent in the pressure dependence on KrF yield. A quantitative Rigrod analysis and comparison is provided at the peak oscillator yield conditions for both, oscillator and amplifier, configurations. Continuous operation of the KrF laser at 300 J has lasted for 2.5 hours without failure at 1 Hz. Successful operation at 5 Hz with 400 J per pulse output has occurred in bursts of 100 seconds. In all of these runs the laser pulse waveform is extremely consistent from the first shot to the last.