Experimental study of a low-order wavefront sensor for high-contrast coronagraphic imagers: results in air and in vacuum

TL;DR

This study evaluates a low-order wavefront sensor's effectiveness in improving contrast in high-contrast coronagraphic imaging, demonstrating significant aberration reduction in air and ongoing tests in vacuum for exoplanet imaging applications.

Contribution

It introduces and tests a low-order wavefront sensor for high-contrast coronagraphs, providing empirical performance data in air and vacuum environments.

Findings

Achieved contrast of 2.8e-7 in air at NASA Ames

Controlled tip/tilt modes at 1 kHz in air

Ongoing vacuum tests to match or surpass air performance

Abstract

For the technology development of the mission EXCEDE (EXoplanetary Circumstellar Environments and Disk Explorer) - a 0.7 m telescope equipped with a Phase-Induced Amplitude Apodization Coronagraph (PIAA-C) and a 2000-element MEMS deformable mirror, capable of raw contrasts of 1e-6 at 1.2 lambda/D and 1e-7 above 2 lambda/D - we developed two test benches simulating its key components, one in air, the other in vacuum. To achieve this level of contrast, one of the main goals is to remove low-order aberrations, using a Low-Order WaveFront Sensor (LOWFS). We tested this key component, together with the coronagraph and the wavefront control, in air at NASA Ames Research Center and in vacuum at Lockheed Martin. The LOWFS, controlling tip/tilt modes in real time at 1~kHz, allowed us to reduce the disturbances in air to 1e-3 lambda/D rms, letting us achieve a contrast of 2.8e-7 between 1.2 and 2 lambda/D. Tests are currently being performed to achieve the same or a better level of correction in vacuum. With those results, and by comparing them to simulations, we are able to deduce its performances on different coronagraphs - different sizes of telescopes, inner working angles, contrasts, etc. - and therefore study its contribution beyond EXCEDE.