Phase mask coronagraphy using a Mach-Zehnder interferometer

Abstract

Aims. We report results obtained with a four-quadrant and an eight-octant phase-mask coronagraphs (4QC and 8OC) produced using amplitude masks inside a Mach-Zehnder interferometer (MZI). We describe the laboratory implementation of these coronagraphs operated in laser light and provide a detailed comparison between theory and experiment. Methods. The +1 and -1 (π phase) amplitude transmissions required to produce a 4QC or an 8OC were obtained using complementary binary-masks (transmission of 1 or 0 for quadrants of similar parities) in the two arms of a MZI, taking advantage of the achromatic π phase shift between the two paths. In one output of the MZI, the reconstructed image of the focal plane is similar to those obtained for sectorised phase-masks coronagraphs, and the image of the aperture corresponds to the characteristic patterns of the 4QC/8OC coronagraphs. Results. Observations are compared with the theory published by other authors and developed further here. The expressions for the light diffracted outside the aperture image are simplified using the Zernike radial polynomials Z 1 n instead of the rapidly diverging hypergeometric functions otherwise used. Experimental results are found to be in very good agreement with the theory. With the present laboratory experiment, about 99% of the light is rejected outside the Lyot stop and the contrast obtained beyond 5λ/D is higher than 10 5 for both the 4QC and 8OC. As expected, the 8OC is less affected by a pointing error than the 4QC, but more sensitive to an aperture central obstruction. Incidently, the loss of transmission for a planet crossing two phase masks is given theoretically as a function of the Lyot stop size, in agreement with observations.

Multi-stage four-quadrant phase mask: achromatic coronagraph for space-based and ground-based telescopes

“…These stellar attenuations are not sufficient when exoplanet detections require at least τ < 10 −4 . Several solutions have been proposed to build achromatic FQPM (e.g., Bloemhof 2005;Mawet et al 2006;Carlotti et al 2009). The multi-stage four-quadrant phase mask (Baudoz et al 2008) that we study in this paper is a part of these solutions.…”

Achromatic Eight-Octant Phase-Mask Coronagraph Using Photonic Crystal

“…Carlotti et al (2009) demonstrate that perfect elimination can be realized for a pointlike star when the number of segments of the phase mask is 4m (m is a non-zero positive integer), and the EOPM is the case of m = 2. The EOPM is put on a telescope focal plane to create zero intensity over a telescope-pupil region on a relayed pupil plane.…”

ARC: an Achromatic Rotation-shearing Coronagraph

“…To achieve the nulling, ARC directly uses the dark fringe of the MZI, while AIC must darken the white fringe of the MI by inserting an achromatic π phase shift in one arm. This dark fringe property of the MZI of behaving like a subtractive device was applied in Aime et al (2007) and Carlotti et al (2008Carlotti et al ( , 2009. For an on-axis point source the achromatic nulling property for AIC and ARC is similar.…”

“…As discussed there, a MZI can be a perfect subtractor, if the beam splitter coefficients r BS and t BS are equal. This is indeed critical and a fine tuning of the effective transmission in each arm of the MZI (and over the whole spectral bandwidth of work) will have to be considered, as proposed in Carlotti et al (2009).…”