The iLocater cryostat and thermal control system: enabling extremely precise radial velocity measurements for diffraction-limited spectrographs

Jonathan Crass; Nandini Sadagopan; Matthew Misch; Alexa Rizika; Brian Sands; Matthew Engstrom; Justin R. Crepp; James Smous; Jeffrey Chilcote; Louis G Fantano; Mike VanSickle; Frederick R. Hearty; Matthew J. Nelson

doi:10.1117/12.2630199

29 August 2022 The iLocater cryostat and thermal control system: enabling extremely precise radial velocity measurements for diffraction-limited spectrographs

Jonathan Crass, Nandini Sadagopan, Matthew Misch, Alexa Rizika, Brian Sands, Matthew Engstrom, Justin R. Crepp, James Smous, Jeffrey Chilcote, Louis G Fantano, Mike VanSickle, Frederick R. Hearty, Matthew J. Nelson

Author Affiliations +

Proceedings Volume 12184, Ground-based and Airborne Instrumentation for Astronomy IX; 121844X (2022) https://doi.org/10.1117/12.2630199
Event: SPIE Astronomical Telescopes + Instrumentation, 2022, Montréal, Québec, Canada

Conference Poster

Abstract

Extremely precise radial velocity (EPRV) measurements are critical for characterizing nearby terrestrial worlds. EPRV instrument precisions of σRV = 1−10 cm/s are required to study Earth-analog systems, imposing stringent, sub-mK, thermo-mechanical stability requirements on Doppler spectrograph designs. iLocater is a new, high resolution (R = 190, 500 median) near infrared (NIR) EPRV spectrograph under construction for the dual 8.4 m diameter Large Binocular Telescope (LBT). The instrument is one of the first to operate in the diffraction-limited regime enabled by the use of adaptive optics and single-mode fibers. This facilitates affordable optomechanical fabrication of the spectrograph using intrinsically stable materials. We present the final design and performance of the iLocater cryostat and thermal control system which houses the instrument spectrograph. The spectrograph is situated inside an actively temperature-controlled radiation shield mounted inside a multi-layer-insulation (MLI) lined vacuum chamber. The radiation shield provides sub-mK thermal stability, building on the existing heritage of the Habitable-zone Planet Finder (HPF) and NEID instruments. The instrument operating temperature (T = 80−100 K) is driven by the requirement to minimize detector background and instantaneous coefficient of thermal expansion (CTE) of the materials used for spectrograph fabrication. This combination allows for a reduced thermomechanical impact on measurement precision, improving the scientific capabilities of the instrument.

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Jonathan Crass, Nandini Sadagopan, Matthew Misch, Alexa Rizika, Brian Sands, Matthew Engstrom, Justin R. Crepp, James Smous, Jeffrey Chilcote, Louis G Fantano, Mike VanSickle, Frederick R. Hearty, and Matthew J. Nelson "The iLocater cryostat and thermal control system: enabling extremely precise radial velocity measurements for diffraction-limited spectrographs", Proc. SPIE 12184, Ground-based and Airborne Instrumentation for Astronomy IX, 121844X (29 August 2022); https://doi.org/10.1117/12.2630199

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