High Contrast Imaging and Wavefront Control with a PIAA Coronagraph: Laboratory System Validation

TL;DR

This paper demonstrates a laboratory PIAA coronagraph system with active wavefront control achieving high contrast imaging, suitable for exoplanet detection, through detailed calibration and stability analysis.

Contribution

The study presents the first laboratory validation of a PIAA coronagraph with active wavefront control achieving high contrast and stability, advancing exoplanet imaging technology.

Findings

Achieved 2.27e-7 raw contrast in laboratory conditions.

Controlled wavefront errors to 3.5e-9 contrast over 4 hours.

Separated residual light into dynamic and static components.

Abstract

The Phase-Induced Amplitude Apodization (PIAA) coronagraph is a high performance coronagraph concept able to work at small angular separation with little loss in throughput. We present results obtained with a laboratory PIAA system including active wavefront control. The system has a 94.3% throughput (excluding coating losses) and operates in air with monochromatic light. Our testbed achieved a 2.27e-7 raw contrast between 1.65 lambda/D (inner working angle of the coronagraph configuration tested) and 4.4 lambda/D (outer working angle). Through careful calibration, we were able to separate this residual light into a dynamic coherent component (turbulence, vibrations) at 4.5e-8 contrast and a static incoherent component (ghosts and/or polarization missmatch) at 1.6e-7 contrast. Pointing errors are controlled at the 1e-3 lambda/D level using a dedicated low order wavefront sensor. While not sufficient for direct imaging of Earth-like planets from space, the 2.27e-7 raw contrast achieved already exceeds requirements for a ground-based Extreme Adaptive Optics system aimed at direct detection of more massive exoplanets. We show that over a 4hr long period, averaged wavefront errors have been controlled to the 3.5e-9 contrast level. This result is particularly encouraging for ground based Extreme-AO systems relying on long term stability and absence of static wavefront errors to recover planets much fainter than the fast boiling speckle halo.