The Shack-Hartmann wavefront sensor (SHWFS) is widely used in an adaptive optics (AO) system to measure the wavefront. The measurement accuracy of the SHWFS is limited by the micro-lens array, which is a core component of it. A deflectometry system (DS) is constructed to offer a high resolution measurement for the AO system, which could be used to test the surface shape of the deformable mirror (DM). The configuration and principle of the DS are presented. The surface shape testing and close-loop performance are analyzed in simulation and experiment. Results show that the DS has good ability in surface shape testing and close-loop correction.
We investigate the distortion caused by the differences between the working environment and the mounting temperature in the surface shape of the deformable mirror (DM) used in the National Ignition Facility. The characteristics of the surface distortion appeared on the DM under different temperature fields, such as the uniform and gradient working environment temperature, are studied in theory and experiments. Under the uniform working environment temperature, the distorted surface shape reveals the high-frequency and actuator-corresponding characteristics. The distorted surface shapes and their dependence on the actuators’ distribution and structural parameters of the DM are analyzed by using the finite element method. The analysis on the distorted surface shape under the gradient working environment temperature indicates that the changes of the peak and valley (PV) or root-mean-square (RMS) value rely on the temperature gradient as well as the difference between the mirror and the environment with a certain rule. To compensate the temperature induced surface shape distortion (TID), its essential mechanism is analyzed systematically based on the thermal stress characteristics, which shows that the actuators’ tilt caused by the thermal expansion coefficient difference between the mirror and the steel base is the essential reason. An efficient method based on an auxiliary temperature compensation module (TCM) and a hybrid closed-loop control algorithm (HCLA) are presented accordingly. In the simulation and the experiment, the DM’s TID could be effectively depressed and a well-compensated DM surface shape is finally achieved.
A low-cost, compact intracavity deformable mirror (DM) consisting of a mirror unit, a heater unit, a cooler unit and a base unit is proposed to compensate the thermal distortion of a linear resonator passively Q-switched (PQS) laser in this paper. The thermal distortion of the PQS laser is measured using the active deflectometry method. Simulation results indicate that the surface shape of the DM (DMSS) matches well with the measured thermal distortion at the given pumping current. 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.
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