High-resolution visible imaging with piezoelectric deformable secondary mirror: experimental results at the 1.8-m adaptive telescope

Integrating deformable mirrors within the optical train of an adaptive telescope was one of the major innovations in astronomical observation technology, distinguished by its high optical throughput, reduced optical surfaces, and the incorporation of the deformable mirror. Typically, voice-coil actuators are used, which require additional position sensors, internal control electronics, and cooling systems, leading to a very complex structure. Piezoelectric deformable secondary mirror technologies were proposed to overcome these problems. Recently, a high-order piezoelectric deformable secondary mirror has been developed and installed on the 1.8-m telescope at Lijiang Observatory in China to make it an adaptive telescope. The system consists of a 241-actuator piezoelectric deformable secondary mirror, a 192-sub-aperture Shack-Hartmann wavefront sensor, and a multi-core-based real-time controller. The actuator spacing of the PDSM measures 19.3 mm, equivalent to approximately 12.6 cm when mapped onto the primary mirror, significantly less than the voice-coil-based adaptive telescopes such as LBT, Magellan and VLT. As a result, stellar images with Strehl ratios above 0.49 in the R band have been obtained. To our knowledge, these are the highest R band images captured by an adaptive telescope with deformable secondary mirrors. Here, we report the system description and on-sky performance of this adaptive telescope.