Experimental test of a micro-mirror array as an adaptive apodizer for high-contrast imaging

摘要

Direct imaging systems are now designed for specific telescope apertures and specific high-contrast diffraction 2D patterns. Current coronagraphic masks are not adaptive components, and different apertures and science requirements must result in different masks, which always come in a small number in a real-life instrument. Adaptive components would make it possible to adapt to changes in the aperture transmission (which will likely happen on a daily basis with the near future highly segmented telescopes, such as ESO's ELT), as well as to reconfigure at will the high-contrast area for different observation modes. In particular, the prospect of characterizing planets with a known position at a high spectral resolution pushes for adaptive coronagraphs capable of creating high-contrast in a small area of the image plane. Micro-mirror arrays are commercially available MOEMS that may be used as binary adaptive amplitude mask. They adaptively redirect light in either one of two directions using millions of micron-sized, bi-stable mirrors. Their spatial resolutions is compatible with 2D binary apodization patterns, in addition to Lyot stops. We have conducted a series of laboratory tests to assess the compatibility of an off-the-shelf micro-mirror array with high-contrast imaging requirements. This communication first presents the context and the scope of the project. It then details the results of our initial characterization of the device, in particular a measurement of the wavefront aberrations and of the level of scattered light that it introduces. Finally, it presents high-contrast point-spread functions obtained with this device, and summarizes the limitations of current components to derive a possible roadmap for the development of scientific-grade adaptive pupil masks.