Intra-Cavity Adaptive Correction of a Unidirectional Nd:YAG Slab Unstable Travelling-Wave Resonator

The required surface shape of the intra-cavity deformable mirror (DM) is not conjugate with the aberration in an unstable standing-wave resonator, which makes the adaptive correction inside the resonator complicated. In this letter, an unstable travelling-wave resonator structure with an intra-cavity adaptive optics (AO) system is proposed to solve this problem. More specifically, the Shark-Hartmann wavefront sensor (SHWFS) and a 980 nm probe beam are employed to measure the aberration of the Nd:YAG slab during lasing operation. A tip/tilt mirror (TTM) is used to correct the intra-cavity tilt, and a DM is employed to compensate for all the remaining intra-cavity aberration. By placing both the wavefront correctors (DM and TTM) and the Nd:YAG slab in the collimated part of the travelling-wave resonator, the required surface shape of the DM is well conjugate with the measured aberration. Experimental results show the proposed method can effectively improve the performance of solid-state slab lasers. After correction, the output power increased from 1312 W to 1587 W, and the corresponding optical-to-optical efficiency increased from 19.5% to 23.6%. Meanwhile, the beam quality $\beta $ was improved from 9.7 to 1.8.