A 24.6 kW quasi-continuous-wave (QCW) Nd-doped yttrium aluminum garnet (Nd:YAG) slab laser is proposed in this Letter. The laser is based on a stable–unstable hybrid cavity. A stable and an unstable resonator were constructed along orthogonal directions in the aperture of the slab. Due to features of the hybrid cavity, the slab laser achieves both high efficiency of power extraction with excellent beam quality and compactness with simplicity. Average output power of 24.6 kW with 47% optical-to-optical efficiency is achieved in the experiment. The beam quality of the output beam is 1.5 times diffraction limits after correction of adaptive optics. The repetition frequency and pulse width of the laser are 400 Hz and 200 μs.
For a high-power slab solid-state laser, obtaining high output power and high output beam quality are the most important indicators. Adaptive optics systems can significantly improve beam qualities by compensating for the phase distortions of the laser beams. In this paper, we developed an improved algorithm called Adaptive Gradient Estimation Stochastic Parallel Gradient Descent (AGESPGD) algorithm for beam cleanup of a solid-state laser. A second-order gradient of the search point was introduced to modify the gradient estimation, and it was introduced with the adaptive gain coefficient method into the classical Stochastic Parallel Gradient Descent (SPGD) algorithm. The improved algorithm accelerates the search for convergence and prevents it from falling into a local extremum. Simulation and experimental results show that this method reduces the number of iterations by 40%, and the algorithm stability is also improved compared with the original SPGD method.
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