Review of high-contrast imaging systems for current and future ground-based and space-based telescopes III: technology opportunities and pathways

Abstract

The Optimal Optical Coronagraph Workshop at the Lorentz Center in September 2017 in Leiden, the Netherlands gathered a diverse group of 25 researchers working on exoplanet instrumentation to stimulate the emergence and sharing of new ideas. This contribution is the final part of a series of three papers summarizing the outcomes of the workshop, and presents an overview of novel optical technologies and systems that are implemented or considered for high-contrast imaging instruments on both ground-based and space telescopes. The overall objective of high contrast instruments is to provide direct observations and characterizations of exoplanets at contrast levels as extreme as 10 −10 . We list shortcomings of current technologies, and identify opportunities and development paths for new technologies that enable quantum leaps in performance. Specifically, we discuss the design and manufacturing of key components like advanced deformable mirrors and coronagraphic optics, and their amalgamation in "adaptive coronagraph" systems. Moreover, we discuss highly integrated system designs that combine contrast-enhancing techniques and characterization techniques (like high-resolution spectroscopy) while minimizing the overall complexity. Finally, we explore extreme implementations using all-photonics solutions for ground-based telescopes and dedicated huge apertures for space telescopes.

Advances in optical engineering for future telescopes

“…As early as 1941 43 , Werenskiold, an amateur astronomer and telescope builder has recorded that curved spiders on secondary mirror could greatly improve the quality of the planetary observation, followed by similar experimental results from Couder (1952) 44 and Everhart and J. Kantorski (1959) 45 . Until 1984, Richter 46 provided a detailed Fraunhofer diffraction calculation mathematically and proved that a thin, circular arc obscuration with an angle of φ lying in the aperture plane can spread out the flares with the same angle φ in the both sides in the The previously-mentioned research 43−45 , the secondary mirror spiders from Harvey and Ftaclas (1995) 47 , apodized pupils with spatially varying transmission functions 48 , and the diffraction noise caused by straight edges and gratings of hexagonal segment topology 49 indicated that the curved-sided segments might be a good alternative for future large telescopes design. Comparing to the high-contrast imaging systems with hexagonal segmented design and delicate instrument for current and future ground-and space-based telescopes 50 , Breckinridge suggested a KISS (Keep It Simple for Space) rule with pinwheel pupil concept for space telescope design 51 .…”

SLM-based digital adaptive coronagraphy: current status and capabilities

“…The outcome of the discussions that occurred during the splinter session dedicated to active coronagraphy are summarized here below, while the reader also interested in the other topics reviewed during this workshop should refer to the corresponding summary papers. [9][10][11] In essence, three different -yet complementary -usage scenarios of active dynamically-reprogrammable coronagraphs can be differentiated, to tackle various challenges:…”

“…As mentioned in §1, various observational strategies (ADI, SDI, PDI) to estimate the stellar PSF and subtract it from the reduced science product can be employed, but all these schemes have in common that they tend to increasingly lose effectiveness at close angular separation. To address this issue, various WFS have been proposed or implemented to measure NCPAs along the scientific beam train, 11 either in an interleaved fashion before or in-between science observations, or in real-time during the scientific exposures. The wavefront correction is then generally achieved by adding centroid offsets to the AO DM solution.…”

Minimizing the Polarization Leakage of Geometric-phase Coronagraphs with Multiple Grating Pattern Combinations

“…Detecting and characterizing these young planets with direct imaging, already requires a large-aperture telescope, high-precision wavefront sensing and correction, a coronagraph with a small inner working angle to suppress the stellar diffraction halo by masking or diffracting stellar light, advanced observational and data-reduction strategies (e.g. angular differential imaging (ADI) and spectral differential imaging (SDI)), and intricate optical measurement systems, such as integral field spectrographs (IFSs) and polarimetry (Marois et al, 2006;Racine et al, 1999;Ruane et al, 2018;Jovanovic et al, 2018;Snik et al, 2018).…”