The wavefront can keep stable while the laser system is adjusted well. Based on this characteristic, in order to improve the beam quality, we suggest to make mirror of free-form surface to compensate for the laser wavefront aberration. First, the theory of aberration compensated with free-form shape mirror is introduced, then through computer simulation, the mirror’s capability of is discussed, lastly, the mirror is used by laser system which the average output power is 12.5KW. By the using of free-form shape mirror, laser’s wavefront, beam quality of farfield and intensity of nearfield are improved obviously: the intensity of nearfield F is improved from 0.15 to 0.39; the wavefront’s PV is improved from 6.3μm to 1.7μm; the wavefront’s rms is improved from 2.0μm to 0.4μm; the beam quality of farfield β is improved from 5.25 to 1.8. Compared with deformable mirror of adaptive optics, the free-form shape mirror has its own advantage: low cost; with no increase to laser system complication; the free-from shape mirror can be used to compensated for high order wavefront aberration effectively.
Stochastic Parallel Gradient Descent(SPGD) algorithm can optimize the system exhibition firsthand without using of wavefront sensor, it predigests the adaptive optic system. Based on SPGD algotithm, a model with 32 element demormable mirror was simulated, the capability of correct toward static aberration and convergence of SPGD algorithm are analysed, the relationship of gain coefficient, stochastic perturbation amplitude are discussed, an adaptive adjustment of gain coefficient is proposed, and it can improve convergence rate effectively.