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 bot h high extraction efficiency and overall gain. A diode-pumped slab amplifie r with a single-pass small-signal gain of 2.5 is used in a 18-pass mode to amplify an input pulse from 50 muJ to 50 mJ, extracting approximately 22% o f the stored energy. A stimulated Brillouin-scattering phase-conjugate mirr or provides isolation from amplified spontaneous emission, prevents gain de pletion, and also ensures good beam quality. The system can be operated fro m 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 hig her-power systems.