First results of the non-common path aberration correction in the Evanescent Wave Coronagraph testbed

Abstract

The Evanescent Wave Coronagraph uses a focal plane mask comprising a lens and a prism placed in contact so that frustrated total internal reflection can occur -the principle governing starlight attenuation. This type of Lyot coronagraph has three main capabilities: i) the mask adapts itself to the wavelength, ii) the size of the mask is adjustable by pressure adjustment, and iii) both the light coming from the star and companion can be collected simultaneously. Previous experimental results, obtained without adaptive optics and in unpolarized light, showed a raw contrast of 10 −4 at 3 λ/D in the I-band and at 4 λ/D in the R-band. Its performance has been limited so far by uncorrected residual aberrations of the optical bench that generate speckles close to the inner working angle. To study the mask performances close to the diffraction limit and compare them with theoretical models, a deformable mirror is installed in the optical path of the testbed to perform wavefront correction. In this work, we report the results obtained in the laboratory using this upgraded setup. We show the preliminary results of correcting the non-common path aberrations using the scientific camera as the wavefront sensor and compare them with expected theoretical performances. The corrections are applied after finding the optimal commands that maximize the variance at the detector plane.