Objective Solar telescopes are important equipment for conducting solar physics research and predicting space weather. During operation, large aperture solar telescope systems are affected by factors such as optical and mechanical structural deformation caused by solar radiation, gravitational deflection in different directions, wind-borne optical structural deformation, and environmental temperature changes, resulting in wavefront aberrations, leading to significant degradation in the imaging quality of the solar telescope system, and restricting the resolution of solar atmospheric imaging. Adaptive optical systems are the main means of correcting low spatio-temporal frequency aberrations during the operation of solar telescopes, but their correction of low-order aberrations wastes a large amount of travel and sacrifices their ability to correct high-order aberrations. Therefore, it is necessary to correct the low spatio-temporal frequency aberrations during the operation of the solar telescope without increasing the complexity of the solar telescope system.
Methods A simulation system and an experimental system have been established for the 60 cm POST solar telescope system. The sensitivity matrix of the displacement of the secondary mirror rigid body is calculated, and the low spatio-temporal frequency aberration is introduced using a deformable mirror to simulate low-order aberrations. The aberration of the optical system's field of view on the axis is observed using a Hartmann camera. The displacement of the secondary mirror rigid body required for correcting the aberration is calculated using the sensitivity matrix method. Finally, the introduced low spatio-temporal frequency aberration is corrected by adjusting the position of the secondary mirror rigid body. The results of the system fine assembly are shown (Fig.4).
Results and Discussions The low spatio-temporal frequency aberrations for simulated solar telescope systems are corrected, the ability of secondary mirror rigid body displacement is quantitatively analyzed to correct different types of low-order aberrations, and the principles for correcting low spatio-temporal frequency aberrations are provided. The simulation results are verified through experiments, where the RMS value of the aberration after correction for the position mismatch error of the secondary mirror pair is lower than 9% of the original value (Fig.9), the RMS value of the aberration after correction for the non-mismatch error is lower than 40% of the original value (Fig.10), and the RMS value of the aberration after correction for the multi-source mixing error is lower than 15% of the original value (Fig.11).
Conclusions A wavefront correction algorithm and implementation system for specific scenes have been constructed with adaptive optics. The real-time wavefront correction has been completed using a hexapod driven secondary mirror. The studies of correction for position mismatch error, non-mismatch error, and multi-source mixed error have been conducted, and multiple sets of experiments have been conducted. Without increasing the complexity of the optical system, the low spatio-temporal frequency aberration of the system has been reduced, and the imaging resolution of the solar telescope has been improved. The secondary mirror rigid body displacement correction method can reduce the low spatio-temporal frequency aberration during the operation of solar telescope systems without adding optical components, and has good development prospects and application value.
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