A Novel Hexpyramid Pupil Slicer for an ExAO Parallel DM for the Giant Magellan Telescope

TL;DR

This paper introduces a novel hexpyramid pupil slicer for the GMT's extreme adaptive optics system, enabling parallel operation of multiple deformable mirrors for unprecedented wavefront control.

Contribution

It presents a new optical architecture with a hexpyramid pupil slicer and multiple DMs working in parallel, vastly increasing actuator count for ELT adaptive optics.

Findings

Design achieves high-quality wavefront correction (lambda/10 surface PV)

Optical system maintains polarization independence and no vignetting

Mechanical mounting structure fabricated with invar for stability

Abstract

The 25.4m Giant Magellan Telescope (GMT) will be amongst the first in a new series of segmented extremely large telescopes (ELTs). The 25.4 m pupil is segmented into seven 8.4 m circular segments in a flower petal pattern. At the University of Arizona we have developed a novel pupil slicer that will be used for ELT extreme adaptive optics (ExAO) on the up and coming ExAO instrument, GMagAO-X. This comes in the form of a six-sided reflective pyramid with a hole through the center known as a "hexpyramid". By passing the GMT pupil onto this reflective optic, the six outer petals will be sent outward in six different directions while the central segment passes through the center. Each segment will travel to its own polarization independent flat fold mirror mounted on a piezoelectric piston/tip/tilt controller then onto its own commercial 3,000 actuator deformable mirror (DM) that will be employed for extreme wavefront control. This scheme of seven DMs working in parallel to produce a 21,000 actuator DM is a new ExAO architecture that we named a "parallel DM," in which the hexpyramid is a key optical component. This significantly surpasses any current or near future actuator count for any monolithic DM architecture. The optical system is designed for high-quality wavefront (lambda/10 surface PV) with no polarization errors and no vignetting. The design and fabrication of the invar mechanical mounting structure for this complex optical system is described in this paper.