Broadband Focal Plane Wavefront Control of Amplitude and Phase Aberrations

TL;DR

This paper advances broadband wavefront control using the Stroke Minimization algorithm with multiple DMs, improving estimation accuracy across wavelengths to achieve symmetric dark holes over larger bandwidths.

Contribution

It introduces an improved wavelength extrapolation method for the Stroke Minimization algorithm, enhancing broadband correction performance with multiple deformable mirrors.

Findings

Enhanced wavelength extrapolation improves broadband dark hole creation.

Multiple DMs can directly estimate electric fields over narrow bandwidths.

Laboratory upgrades better simulate broadband starlight for testing.

Abstract

The Stroke Minimization algorithm developed at the Princeton High Contrast Imaging Laboratory has proven symmetric dark hole generation using minimal stroke on two deformable mirrors (DM) in series. The windowed approach to Stroke Minimization has proven symmetric dark holes over small bandwidths by using three wavelengths to define the bandwidth of correction in the optimization problem. We address the relationship of amplitude and phase aberrations with wavelength, how this changes with multiple DMs, and the implications for simultaneously correcting both to achieve symmetric dark holes. Operating Stroke Minimization in the windowed configuration requires multiple wavelength estimates. To save on exposures, a single estimate is extrapolated to bounding wavelengths using the established relationship in wavelength to produce multiple estimates of the image plane electric field. Here we demonstrate better performance by improving this extrapolation of the estimate to other wavelengths. The accuracy of the functional relationship will ultimately bound the achievable bandwidth, therefore as a metric these results are also compared to estimating each wavelength separately. In addition to these algorithm improvements, we also discuss a laboratory upgrade and how it can better simulate broadband starlight. We also discuss the possibility of leveraging two DMs in series to directly estimate the electric field over a narrow bandwidth and the challenges associated with it.