Concept validation of a high dynamic range point-diffraction interferometer for wavefront sensing in adaptive optics

TL;DR

This paper validates a high dynamic range point-diffraction interferometer for wavefront sensing in adaptive optics, demonstrating its accuracy, control capabilities, and robustness with monochromatic and polychromatic light in exoplanet imaging.

Contribution

It provides experimental validation of the m-PDI concept, showing its effectiveness for high-contrast adaptive optics wavefront correction.

Findings

Residual error of 7.7nm-rms in correction.

Achieved Strehl ratio > 0.7 with polychromatic light.

No performance drop with broadband light.

Abstract

The direct detection and imaging of exoplanets requires the use of high-contrast adaptive optics (AO). In these systems quasi-static aberrations need to be highly corrected and calibrated. In order to achieve this, the pupil-modulated point-diffraction interferometer (m-PDI), was presented in an earlier paper. This present paper focuses on m-PDI concept validation through three experiments. First, the instrument's accuracy and dynamic range are characterised by measuring the spatial transfer function at all spatial frequencies and at different amplitudes. Then, using visible monochromatic light, an adaptive optics control loop is closed on the system's systematic bias to test for precision and completeness. In a central section of the pupil with 72% of the total radius the residual error is 7.7nm-rms. Finally, the control loop is run using polychromatic light with a spectral FWHM of 77nm around the R-band. The control loop shows no drop in performance with respect to the monochromatic case, reaching a final Strehl ratio larger than 0.7.