Alignment of three mirror anastigmat telescopes using a multilayered stochastic parallel gradient descent algorithm

When a telescope doesn’t reach a reasonable point spread function on the detector or detectable wavefront quality after initial assembly, a coarse phase alignment on-sky is crucial. Before utilizing a closed loop adaptive optics system, the observatory needs a strategy to actively align the telescope to align the telescope sufficiently for fine wavefront sensing (WFS). This paper presents a method of early-stage alignment using stochastic parallel-gradient-descent (SPGD) which performs random perturbations to the TMA telescope optics. The SPGD algorithm will drive the telescope until the wavefront error is below the acceptable range of the fine AO system to hand the telescope over. The focused spot size over the field is adopted as a feed parameter to SPGD algorithm and wavefront peak-to-valley error values are monitored to directly compare our mechanical capabilities to our alignment goal of diffraction limited imaging and fine wavefront sensing.