Apodized Pupil Lyot Coronagraphs for Arbitrary Apertures. Iv. Reduced Inner Working Angle and Increased Robustness to Low-Order Aberrations

Abstract

The Apodized Pupil Lyot Coronagraph (APLC) is a diffraction suppression system installed in the recently deployed instruments Palomar/P1640, Gemini/GPI, and VLT/SPHERE to allow direct imaging and spectroscopy of circumstellar environments. Using a prolate apodization, the current implementations offer raw contrasts down to 10 −7 at 0.2 arcsec from a star over a wide bandpass (20%), in the presence of central obstruction and struts, enabling the study of young or massive gaseous planets. Observations of older or lighter companions at smaller separations would require improvements in terms of the inner working angle (IWA) and contrast, but the methods originally used for these designs were not able to fully explore the parameter space. We propose a novel approach to improve the APLC performance. Our method relies on the linear properties of the coronagraphic electric field with the apodization at any wavelength to develop numerical solutions producing coronagraphic star images with high-contrast region in broadband light. We explore the parameter space by considering different aperture geometries, contrast levels, dark-zone sizes, bandpasses, and focal plane mask sizes. We present an application of these solutions to the case of Gemini/GPI with a design delivering a 10 −8 raw contrast at 0.19 arcsec and offering a significantly reduced sensitivity to low-order aberrations compared to the current implementation. Optimal solutions have also been found to reach 10 −10 contrast in broadband light regardless of the aperture shape, with effective IWA in the 2-3.5 λ/D range, therefore making the APLC a suitable option for the future exoplanet direct imagers on the ground or in space.

Polynomial Apodizers for Centrally Obscured Vortex Coronagraphs

“…To find the maximum total energy throughput achievable by a charge 4 or higher PAVC for a given R S , one would have to use a non-linear optimizer rather than the linear programming routine we use here. For this reason, maximizing transmission instead of throughput is a commonly used method to linearize problems involving optimizing apodized coronagraph designs Carlotti et al 2012;N'Diaye et al 2015). Therefore, we use T as the FOM for charge 4 and 6 PAVCs, while bearing in mind that we may overlook solutions to Equations 12 and 13 that produce higher total energy throughputs than we report.…”

“…Other approaches involve a combination of modifications to the pupil and focal plane geometries of the coronagraph, both to improve coronagraphic performance for unobstructed pupils and to compensate for complicated pupils. For example, the apodized pupil Lyot coronagraph (APLC) modifies the Lyot coronagraph by introducing a pupil apodizing mask in order to improve starlight suppression for broadband light with an obstructed pupil (Soummer 2005;N'Diaye et al 2015).…”

The LUVOIR architecture ``A'' coronagraph instrument

“…We set the inner edge of the DH hole to be smaller than the outer edge of the focal plane makes in order to make the design robust to stellar angular size and misalignments. 37 Because it is hard to design and apodizer with sufficient throughput that covers the entire possible HZ illustrated on Fig. 2, we designed coronagraph for a suite of focal plane masks, with varying IW A DH and OW A DH , assuming that the masks will be chosen as a function of the distance to each observed host star ( Fig.…”

Comparison of wavefront control algorithms and first results on the high-contrast imager for complex aperture telescopes (hicat) testbed

“…New coronagraph designs are currently developed in simulation [5,6,7] for a next implementation on the testbed. The wavefront control of HiCAT will also consist in two deformable mirrors (DM) pupil-remapping techniques (e.g.…”