Efficient High-Gain Laser Amplification from a Low-Gain Amplifier by use of Self-Imaging Multipass Geometry

We characterize a self-imaging multipass amplifier scheme that provides both high extraction efficiency and overall gain. A diode-pumped slab amplifier with a single-pass small-signal gain of 2.5 is used in a 16-pass mode to amplify an input pulse from 50 muJ to 50 mJ, extracting approximately 22% of the stored energy. A stimulated Brillouin-scattering phase-conjugate mirror provides isolation from amplified spontaneous emission, prevents gain depletion, and also ensures good beam quality. The system can be operated from 10 Hz to in excess of 450 Hz, with modest changes in the beam quality and energy. The scheme has the potential to be scaled to higher-energy and higher-power systems.