High Speed Focal Plane Wavefront Sensing with an Optical Chopper

TL;DR

This paper introduces a novel high-speed focal plane wavefront sensing method using an optical chopper, enabling simultaneous science imaging and wavefront correction at up to 50% duty cycle, validated through simulations and laboratory tests.

Contribution

It presents a new wavefront sensing technique that uses an optical chopper for amplitude modulation, allowing fast, simultaneous science imaging and wavefront correction without non-common path errors.

Findings

Achieved up to 50% science imaging duty cycle with the technique.

Validated the method through simulations and laboratory experiments.

Demonstrated resolving sine ambiguity of wavefront modes at various frequencies.

Abstract

Focal plane wavefront sensing and control is a critical approach to reducing non-common path errors between the a conventional astronomical adaptive optics (AO) wavefront sensor (WFS) detector and science camera. However, in addition to mitigating non-common path errors, recent focal plane wavefront sensing techniques have been developed to operate at speeds fast enough to enable "multi-WFS" AO, where residual atmospheric errors are further corrected by a focal plane WFS. Although a number of such techniques have been recently developed for coronagraphic imaging, here we present one designed for non-coronagraphic imaging. Utilizing conventional AO system components, this concept additionally requires (1) a detector imaging the focal plane of the WFS light source and (2) a pupil plane optical chopper device that is non-common path to the first WFS and is synchronized to the focal plane imager readout. These minimal hardware requirements enable the temporal amplitude modulation to resolve the sine ambiguity of even wavefront modes for both low, mid, and high wavefront spatial frequencies. Similar capabilities have been demonstrated with classical phase diversity by defocusing the detector, but such techniques are incompatible with simultaneous science observations. This optical chopping technique, however, enables science imaging at up to a 50% duty cycle. We present both simulations and laboratory validation of this concept on SEAL, the Santa Cruz Extreme AO Laboratory testbed.