The 85-electrode adaptive optics system of the Swedish 1-m Solar Telescope

¹ Institute for Solar Physics, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden
e-mail: scharmer@astro.su.se
² Stockholm Observatory, Department of Astronomy, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden
³ Royal Swedish Academy of Sciences, Box 50005, 104 05 Stockholm, Sweden
⁴ CILAS, 8 Avenue Buffon, CS 16319, 45063 Orléans Cedex 2, France
⁵ Lens Tech AB, Tallbackagatan 11, 931 64 Skellefteå, Sweden

Received: 3 June 2019
Accepted: 12 February 2024

Abstract

We discuss the chosen concepts, detailed design, implementation and calibration of the 85-electrode adaptive optics (AO) system of the Swedish 1-meter Solar Telescope (SST), which was installed in 2013. The AO system is unusual in that it uses a combination of a monomorph mirror with a Shack-Hartmann (SH) wavefront sensor (WFS) and a second high-resolution SH microlens array to aid the characterization, calibration, and modal control of the deformable mirror. An Intel PC workstation performs the heavy image processing associated with cross-correlations and real-time control at a 2 kHz update rate with very low latency. The computer and software continue the successful implementation since 1995 of earlier generations of correlation tracker and AO systems at SST and its predecessor, the 50-cm Swedish Vacuum Solar Telescope, by relying entirely on work-station technology and an extremely efficient algorithm for implementing cross-correlations with the large field of view of the WFS. We describe critical aspects of the design, calibrations, software, and functioning of the AO system. The exceptionally high performance is testified through the highest Strehl ratio (inferred from the measured granulation contrast) of existing meter-class solar telescopes, as demonstrated here at wavelengths shorter than 400 nm and discussed in more detail in a previous separate publication We expect that some aspects of this AO system may also be of interest outside the solar community.