Atmospheric Pressure Operation of a KrF Laser Oscillator and Amplifier with a Krypton-Rich Mixture and a Kr/F2 Mixture

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Abstract
Atmospheric pressure operation of the electron-beam (e-beam)-excited KrF laser can greatly reduce the design constraints on a large-aperture laser module in the megajoule-class system as an inertial confinement fusion driver. The krypton-rich and Kr/F2 mixtures are suitable for the atmospheric pressure operation because these can produce high specific output energy without serious reduction of the intrinsic efficiency compared with conventional argon-rich mixtures. A 50-ns e-beam generator was used to pump the KrF laser oscillator by which fundamental studies of the KrF laser with atmospheric pressure krypton-rich mixtures were performed. A larger apparatus, using another 65-ns e-beam generator, demonstrated the specific output energy of 6.6 J/ℓ from a Kr/F2 mixture with an intrinsic efficiency of 6%. The latter apparatus was then used as an oscillator-amplifier system to investigate the amplifier characteristics of the KrF laser because the atmospheric pressure krypton-rich mixture is useful for large amplifier modules. In this oscillator-amplifier experiment, the power efficiency (extracted intensity divided by excitation rate and active length) in excess of 10% was obtained for krypton-rich mixtures.