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Forging Advanced Liquid-Crystal Coronagraphs Optimized for Novel Exoplanet Research

Periodic Reporting for period 4 - FALCONER (Forging Advanced Liquid-Crystal Coronagraphs Optimized for Novel Exoplanet Research)

Reporting period: 2020-10-01 to 2021-03-31

In the ERC StG project FALCONER we have developed novel coronagraphic components and optical systems based on patterned liquid-crystal technology. The overall aim is to enable direct imaging of exoplanets, and moreover the characterization of the atmospheres of exoplanets through spectroscopy and polarimetry. We mainly focus on the so-called vector-APP coronagraph, which is a pupil-plane phase mask that delivers two complementary point-spread functions with dark holes in which exoplanets can be observed. During this project, we have designed, tested, and implemented new coronagraphic masks with unprecedented contrast performance over large spectral bandwidths. Specifically, we have developed vAPP coronagraphs for Subaru/SCExAO, LBT/LMIRcam, WHT/LExI, MagAO-X, VLT/ERIS and the balloon experiment HiCIBaS. Moreover, we have designed vAPP coronagraphs for the ELT instruments MICADO and METIS. With our novel multiple-grating technique we have invented a generic solution for the polarization-leakage problem of such devices, with promising applications also for focal-plane coronagraphs like the Vector Vortex Coronagraph, particularly for space-based implementation for future direct observations of potentially habitable exoplanets orbiting solar-type stars. With the complex phase patterns enabled by the liquid-crystal technology, we have fully incorporated wavefront sensing from the focal plane.
Moreover, we have applied the same liquid-crystal technology to develop the optimal vector-Zernike wavefront sensor, Holographic Aperture Masking spectroscopic interferometry (installed at Keck/OSIRIS), and novel polarimetric approaches for remote-sensing of life.
In addition, the FALCONER team has provided the first 3-4 um spectra of HR8799 c,d,e with the vAPP360 at LBT, has provided the first direct discovery of a polarization signal of a substellar companion (DH Tau b; due to the presence of a circumplanetary disk), and has contributed to the direct detections of exoplanets YSES1b&c and YSES2b. Finally, FALCONER researchers have developed new polarimetric techniques and instrumentations for the unambiguous discovery of life through the circular polarization signatures of homochiral biomolecules, and are building instruments for the ISS and a lunar lander to test these techniques on planet Earth.
We have successfully developed vector-APP coronagraphs covering a large range of wavelengths from 500 nm to 5 um, for LBT/LMIRcam, Subaru/SCExAO, WHT/LExI, Magallan/MagAO-X, VLT/ERIS, and the balloon experiment HiCIBaS. We have designed vector-APP coronagraphs for ELT/MICADO and ELT/METIS. The vAPP coronagraphs at LBT and Subaru have been fully commissioned, and are deployed for scientific observations (first 3-4 um spectra of HR8799c,d,e with LBT vAPP360) and further tech development (implementation of focal-plane wavefront sensing and dark-hole control at SCExAO).
We have invented a number of novel optical techniques for high-contrast imaging: the multiple-grating technique to suppress leakage light in vector-APP and Vector Vortex Coronagraphs by orders of magnitude, the vector-Zernike wavefront sensor that simultaneously measures phase and amplitude aberrations. Both techniques are highly promising for future space telescopes that will be able to perform direct observations of potentially habitable exoplanets orbiting solar-type stars.
We have invented "Holographic Amplitude Masking" that offers multiplexed spectroscopic interferometry, and have successfully implemented and commissioned this at Keck.
With VLT/SPHERE we have performed a polarimetric survey of known companions (indicating circumplanetary dust structure or structured clouds), which has led to the first detection (DH Tau b), and upper limits for the HR8799 planets.
We have developed novel polarimetric measurement techniques and instruments for remote detection of life. After successful demonstration in the field of circular spectropolarimetry as an unambiguous indicator of homochirality, we are building the LSDpol and LOUPE instruments to perform spectropolarimetry of the entire Earth from the ISS and the Moon, respectively.

See also and
The FALCONER project has provided major breakthroughs in coronagraphic optics, wavefront sensing, and polarimetry for direct exoplanetary observations, which are enabled by the unique broad-band performance and extreme patterns enabled by novel liquid-crystal technology. These optics can therefore operate over unprecedented broad spectral ranges, and are therefore very effective for broad-band imaging, and for (integral-field) spectroscopy. Moreover, we implement extreme phase patterns (radical freeform and/or holographic) that allow us to manipulate light in ways previously unimaginable, for instance to combine coronagraphic dark-hole performance with efficient information contained in the bright field to keep the dark hole dark. We have invented the multiple-grating technique to generically solve the polarization-leakage issues of such liquid-crystal devices, such that the coronagraphic optics are not limiting contrast and perform over wavelength ranges as wide as an entire octave. These liquid-crystal techniques have driven our inventions of the vector-Zernike wavefront sensor (which is the most efficient broadband sensor for both phase and amplitude aberrations), and Holographic Aperture Masking (which uses most of the light from a telescope to turn it into a spectroscopic interferometer with twice the spatial resolution.
vAPP coronagraph + multi-wavelength PSF at Subaru-SCExAO