Intracavity deformable mirror for beam quality improvement and power enhancement of a passively Q-switched laser

The performance of the passively Q-switched (PQS) laser deteriorates under high pumping power for the intracavity thermally induced wavefront distortion (thermal distortion for short). A new intracavity deformable mirror (DM) is proposed to compensate the thermal distortion of a PQS laser in this paper. The thermal distortion of the PQS laser is measured using the active deflectometry method. A simulation model is built to investigate the influences of the DM structure parameters on the surface shape of the DM (DMSS). Simulation results indicate that the DMSS matches well with the measured thermal distortion in the PQS laser at the given pumping current. Based on the simulation results, a low-cost, compact intracavity DM consisting of a mirror unit, a heater unit, a cooler unit and a base unit is built and used in the PQS laser. The DMSS is measured by a Zygo interferometer and coincides with the simulation result. In the improved PQS laser experiment, the optimum heater temperatures for the maximum output power and minimum M² at different pumping currents are measured and given. The output stability of the PQS laser with the DM is tested. By adjusting the heater temperature, the PQS laser could achieve optimum performance in different environmental temperatures with good temperature adaptability. Experiment results verify that the PQS laser with the designed DM could achieve high output power and good beam quality at high pumping currents, as the DM prominently compensates the thermal distortion in the laser.