Off-axis aberration correction of liquid mirror telescope based on magnetic fluid deformable mirror and a spherical mirror

Liquid Mirror Telescope (LMT) has become a viable alternative to traditional telescopes in astronomical exploration and other fields. Due to liquid property limitations, LMT cannot be tilted as the traditional telescopes when it observes the sky. In order to expand the observation field of LMT, the off-axis aberration must be compensated. In this paper, an adaptive optics system having a spherical mirror and a magnetic fluid deformable mirror (MFDM) is designed to compensate the large aberrations of a 3-m f/4 LMT observing at an off-axis angle of 10 degrees from the zenith. The spherical mirror is used to correct the lower order aberrations and is placed at a certain distance away from the LMT optical axis. MFDM is a new type of wavefront corrector which is used to correct the residual aberrations of the corrected off-axis aberration. The designed MFDM has a radius of 100 mm with 1141 magnetic coils as the actuator. A Maxwell coil is placed on the periphery of the MFDM to generate a large uniform magnetic field so that the response of actuators can be driven linearly. The off-axis aberration of the LMT is simulated in ZEMAX and the correction ability of the spherical mirror and MFDM is simulated in COMSOL and MATLAB. All simulation results demonstrate that the MFDM combine with a spherical mirror can effectively correct the off-axis aberration of the LMT.