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DARKNESS: The First Microwave Kinetic Inductance Detector Integral Field Spectrograph for Exoplanet Imaging


High-contrast imaging is a powerful technique for the study of exoplanets. Combining extreme adaptive optics to correct for atmospheric turbulence, a coronagraph to suppress diffraction from the telescope aperture, and an integral field spectrograph to obtain a spectrum at every spatial element in the final image, ground-based high contrast instruments can effectively remove on-axis star light to characterize nearby faint companions and disks. Current state-of-the-art high-contrast imagers operating at near-infrared wavelengths regularly achieve contrast ratios < 10−6 at 0.5” separations. For young systems (<~10 Myr) at 10 pc, this roughly translates to detectability of Jupiter mass planets in 5 AU orbits. Tighter separations may be achieved with larger telescope apertures, but deeper contrasts are limited from the ground by residual atmospheric aberrations. Unsensed and uncorrected wavefront aberrations lead to a pattern of coherent speckles in the final image that evolve on a range of timescales from a few milliseconds to tens of minutes. The most problematic speckle population, referred to as atmospheric speckles, have lifetimes of roughly 1 s causing them to average slowly in long exposures. After subtraction of the long lived quasi-static speckles in post-processing, atmospheric speckle noise sets the ultimate contrast limits.

In this thesis we present DARKNESS (the DARK-speckle Near-infrared Energy- resolving Superconducting Spectrophotometer), the first demonstration platform to utilize optical/near-infrared Microwave Kinetic Inductance Detectors (MKIDs) for high-contrast imaging. The photon counting and simultaneous low-resolution spectroscopy provided by MKIDs enable real-time speckle control techniques and post-processing speckle suppression at framerates capable of resolving the atmospheric speckles. We describe the motivation, design, and characterization of DARKNESS, its deployment behind the PALM-3000 extreme adaptive optics system and the Stellar Double Coronagraph at Palomar Observatory, early speckle characterization results at ∼ms timescales, and future prospects for implementing this data in useful speckle removal schemes.

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