Deep Contrast and Companion Detection Using the EvWaCo Test Bed Equipped with an Achromatic Focal Plane Mask and an Adjustable Inner Working Angle

Abstract

The evanescent wave coronagraph uses the principle of frustrated total internal reflection (FTIR) to suppress the light coming from the star and study its close environment. Its focal plane mask is composed of a lens and a prism placed in contact with each other to produce the coronagraphic effect. In this paper, we present the experimental results obtained using an upgraded focal plane mask of the Evanescent Wave Coronagraph (EvWaCo). These experimental results are also compared to the theoretical performance of the coronagraph obtained through simulations. Experimentally, we reach a raw contrast equal to a few 10−4 at a distance equal to 3 λ/D over the full I band (λ c = 800 nm, Δλ/λ ≈ 20%) and equal to 4 λ/D over the full R band (λ c = 650 nm, Δλ/λ ≈ 23%) in unpolarized light. However, our simulations show a raw contrast close to 10−4 over the full I band and R band at the same distance, thus confirming the theoretical achromatic advantage of the coronagraph. We also verify the stability of the mask through a series of contrast measurements over a period of 8 months. Furthermore, we measure the sensitivity of the coronagraph to the lateral and longitudinal misalignment of the focal plane mask and to the lateral misalignment of the Lyot stop.

Inverse problem approach in Extreme Adaptive Optics: analytical model of the fitting error and lowering of the aliasing

“…( 1) to get the structure function after AO correction, it is possible to get h and the long-exposure PSF induced by the residual tting error, h , via Eq. (3). The smaller the wavefront residuals, the closer h will be to a delta function and the closer the long exposure PSF, h, will be to the diraction limited PSF, h tel .…”

“…Based on the frustration of the total internal reection (FTIR 2 ) between a prism and a lens put in contact, the star light is transmitted through the contact area while the light of the stellar vicinity is internally reected in the prism. 3 As the FTIR is chromatic, the mask adapts itself with the wavelength, providing almost achromatic contrast performances over the spectral domain [600 nm, 900 nm]. In addition, the mask shape and size can be adjusted by tuning the pressure between the two pieces of glass.…”

Design, performance, and potential scientific applications of the evanescent wave coronagraph with an adjustable inner working angle

“…We have developed an EvWaCo testbed to measure the contrast performance obtained by the coronagraph using an upgraded focal plane mask. 12 This testbed is on a passive setup and with no adaptive optics installed. In this paper, the raw contrast is calculated by dividing the normalized irradiance by the mask transmission where the normalized irradiance is the ratio between the star residual signal and the star PSF peak.…”

Inverse problem approach in Extreme Adaptive Optics: analytical model of the fitting error and lowering of the aliasing

“…Based on the frustration of the total internal reflection (FTIR 2 ) between a prism and a lens put in contact, the star light is transmitted through the contact area while the light of the stellar vicinity is internally reflected in the prism. 3 As the FTIR is chromatic, the mask adapts itself with the wavelength, providing almost achromatic contrast performances over the spectral domain [600 nm, 900 nm]. In addition, the mask shape and size can be adjusted by tuning the pressure between the two pieces of glass.…”