The high-frequency aberrations (HIFAs) that are corresponding to the actuator array have been reported to exist on the initial surface shape of many deformable mirrors (DMs), such as the bimorph DM, the unimorph DM, the monomorph DM, and the membrane DM. This actuator-corresponding high-frequency aberration (AC-HIFA) could not be corrected effectively by the DM and would limit the correction ability of the DM. In this paper, we presented the AC-HIFA in a stacked array piezoelectric (PZT) DM, which may result in ghost damage that is dangerous in the high power laser system. More importantly, we investigated a solution through simulation and experiment that by using a mirror plate and a long thin post array, which were machined integrally from a piece of BK7 glass, the AC-HIFA could be eliminated completely. In addition, the structural parameters' influences on the AC-HIFA were investigated in the simulation, which could help other researchers to determine appropriate parameters of the mirror and the posts and to make a fine surface shape in their own DMs.

In this Letter, a 10.8 kW, 2.6 times diffraction limited laser based on a continuous wave (CW) Nd:YAG oscillator using an unstable resonator and an extra-cavity adaptive optics system was presented. Two Nd:YAG slabs and a disk-laser configuration were used to make the laser compact and power scalable. The output was a rectangular annulus, which was further expanded to a square annulus and was adaptively corrected by an extra-cavity deformable mirror (DM). The DM was designed to be capable of correcting the square annular wavefront aberrations. In the experiment, the vertical beam quality was improved from 51.7 to 2.6 times diffraction limited after correction. To the best of our knowledge, this is the highest power and brightness based on a CW Nd:YAG oscillator.

Astrophysics and cosmology in the coming decades urgently need a large field-of-view (FOV), highly multiplexed spectroscopic survey telescope satisfying challenging image quality and stability requirements. The 6.5m MUltiplexed Survey Telescope (MUST) proposed by Tsinghua University will be constructed on the Saishiteng Mountain of Northwest China to improve the spectroscopic survey capability of ground-based optical telescopes. In this paper, we demonstrate the conceptual design of the optical system of MUST. MUST will adopt a 6.5m primary mirror, a 2.45m secondary mirror, and a multiple-element widefield corrector (WFC) to ensure excellent image quality with an 80% encircled energy size of image spots less than ~ 0.6 arcsec in diameter for the entire 3° FOV and the whole 50° zenith angle range. Thanks to its compact 6.5m Ritchey-Chretien system and 20000 optical fibers on its Cassegrain focus, MUST will carry out state-of-the-art wide-field spectroscopic surveys with efficiency ~ 19 times higher than the Dark Energy Spectroscopic Instrument (DESI) using a measure proposed by Ellis et al. Upon completion around 2029, MUST will be one of the world's largest and most advanced wide-field spectroscopic survey telescopes and a new essential reference for the future development of wide-field survey telescopes. It will enable significant advances in many fields in astrophysics and cosmology.

We report a novel, to the best of our knowledge, mode-tunable optical vortex generation method based on a mirror curvature dynamically controlled Z-shaped resonant cavity, a mode conversion beamline, and a reference laser beamline. By changing the mirror curvature of an intra-cavity deformable mirror (DM) at a certain pumping voltage and current, various Hermite–Gaussian (HG) mode beams were obtained in the Z-shaped resonant cavity of a laser diode pumped Yb:CALGO laser. The vortex beams were realized finally by using an external cavity astigmatism converter. In the experiment, the dynamic tuning of the 1st to 9th order HG mode beams and Laguerre–Gaussian mode vortex beams carrying different orbital angular momenta, ranging from 1 ℏ to 9 ℏ were achieved by dynamically adjusting the driving voltage of the DM.

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 M 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.