Coherent beam combination of two 120 W solid state lasers with high beam quality

We report a coherent combining of two 120 W solid state lasers with good beam quality. Laser beams from two slab laser amplifiers are reshaped into square beam. Up to 92.4% fill factor is achieved by splicing system with small gaps. A compact optical system with high sampling frequency is designed to detect the optical axis of slab lasers. A fast steering mirror (FSM) system driven by piezoelectric ceramics is applied to stabilizing the lasers. When the FSM systemworks, the root mean square error of the optical axis is significantly reduced to be less that 2 micro radians. The piston phase of two lasers is locked by a fast dithering system based on field programmable gate array (FPGA) using stochastic parallel gradient descent(SPGD) algorithm. After coherent beam combination, the peak intensity of the far-field spot is increased by a factor of 1.7, reaching 84% of the ideal case. When the beams are in phase, the BQ of the combined laser beam is 1.1, which means that more than 67% of the total energy is locked in the main lobe.