Compact 300-J/300-GW Frequency-Doubled Neodymium Glass Laser—Part I: Limiting Power by Self-Focusing

Small-scale self-focusing is the main cause of power limitation in nanosecond Nd:glass lasers. We report pioneer observation in experiment of laser beam noise amplification for $B$ -integral (nonlinear phase) order of unity, i.e., without destruction of nonlinear medium. Analytical dependences of noise amplification coefficient on the $B$-integral have been obtained for one nonlinear medium as well as for two nonlinear media separated by an air gap with image relay. A simple analytical dependence has been found for an optimal distance between two nonlinear media for which the maximum allowable value of $B$ -integral increases from 2.7 to 4.3. The maximum attainable energy in neodymium-phosphate glass lasers with rod amplifiers 10 cm in diameter is 400 J with a pulse duration of 1 ns.