Deformable mirror interferometric analysis for the direct imagery of exoplanets

TL;DR

This paper presents an interferometric analysis of a deformable mirror used in high-contrast exoplanet imaging, focusing on surface characterization, actuator behavior, and defect effects to improve adaptive optics performance.

Contribution

It introduces a detailed interferometric method for analyzing deformable mirror surfaces and actuator interactions, enhancing the understanding of mirror defects and behavior in exoplanet imaging systems.

Findings

Precise surface shape characterization of the deformable mirror.

Analysis of individual actuator behavior and cross-talk effects.

Assessment of surface defects and their impact on wavefront correction.

Abstract

Direct imaging of exoplanet systems requires the use of coronagraphs to reach high contrast levels (10^-8 to 10^-11) at small angular separations (0.1"). However, the performance of these devices is drastically limited by aberrations (in phase or in amplitude, introduced either by atmosphere or by the optics). Coronagraphs must therefore be combined with extreme adaptive optic systems, composed of a focal plane wavefront sensor and of a high order deformable mirror. These adaptive optic systems must reach a residual error in the corrected wavefront of less than 0.1 nm (RMS) with a rate of 1 kHz. In addition, the surface defects of the deformable mirror, inherent from the fabrication process, must be limited in order to avoid the introduction of amplitude aberrations. An experimental high contrast bench has been developed at the Paris Observatory (LESIA). This bench includes a Boston Micromachine deformable mirror composed of 1024 actuators. For a precise analysis of its surface and performance, we characterized this mirror on the interferometric bench developed since 2004 at the Marseille Observatory (LAM). In this paper, we present this interferometric bench as well as the results of the analysis. This will include a precise surface characterization and a description of the behavior of the actuators, on a 10 by 10 actuator range (behavior of a single actuator, study of the cross-talk between neighbor actuators, influence of a stuck actuator) and on full mirror scale (general surface shape).