Highcontrast imaging with an arbitrary aperture: active correction of aperture discontinuities
Abstract
We present a new method to achieve highcontrast images using segmented and/or onaxis telescopes. Our approach relies on using two sequential Deformable Mirrors to compensate for the large amplitude excursions in the telescope aperture due to secondary support structures and/or segment gaps. In this configuration the parameter landscape of Deformable Mirror Surfaces that yield high contrast Point Spread Functions is not linear, and nonlinear methods are needed to find the true minimum in the optimization topology. We solve the highly nonlinear MongeAmpere equation that is the fundamental equation describing the physics of phase induced amplitude modulation. We determine the optimum configuration for our two sequential Deformable Mirror system and show that highthroughput and high contrast solutions can be achieved using realistic surface deformations that are accessible using existing technologies. We name this process Active Compensation of Aperture Discontinuities (ACAD). We show that for geometries similar to JWST, ACAD can attain at least 10^{7} in contrast and an order of magnitude higher for future Extremely Large Telescopes, even when the pupil features a missing segment" . We show that the converging nonlinear mappings resulting from our Deformable Mirror shapes actually damp nearfield diffraction artifacts in the vicinity of the discontinuities. Thus ACAD actually lowers the chromatic ringing due to diffraction by segment gaps and strut's while not amplifying the diffraction at the aperture edges beyond the Fresnel regime and illustrate the broadband properties of ACAD in the case of the pupil configuration corresponding to the Astrophysics Focused Telescope Assets. Since details about these telescopes are not yet available to the broader astronomical community, our test case is based on a geometry mimicking the actual one, to the best of our knowledge.
 Publication:

Techniques and Instrumentation for Detection of Exoplanets VI
 Pub Date:
 September 2013
 DOI:
 10.1117/12.2025123
 Bibcode:
 2013SPIE.8864E..0ZP