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Laboratory Testing and Performance Verification of the CHARIS Integral Field SpectrographThe Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) is an integral field spectrograph (IFS) that has been built for the Subaru telescope. CHARIS has two imaging modes; the high-resolution mode is R82, R69, and R82 in J, H, and K bands respectively while the low-resolution discovery mode uses a second low-resolution prism with R19 spanning 1.15-2.37 microns (J+H+K bands). The discovery mode is meant to augment the low inner working angle of the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) adaptive optics system, which feeds CHARIS a coronagraphic image. The goal is to detect and characterize brown dwarfs and hot Jovian planets down to contrasts five orders of magnitude dimmer than their parent star at an inner working angle as low as 80 milliarcseconds. CHARIS constrains spectral crosstalk through several key aspects of the optical design. Additionally, the repeatability of alignment of certain optical components is critical to the calibrations required for the data pipeline. Specifically the relative alignment of the lens let array, prism, and detector must be highly stable and repeatable between imaging modes. We report on the measured repeatability and stability of these mechanisms, measurements of spectral crosstalk in the instrument, and the propagation of these errors through the data pipeline. Another key design feature of CHARIS is the prism, which pairs Barium Fluoride with Ohara L-BBH2 high index glass. The dispersion of the prism is significantly more uniform than other glass choices, and the CHARIS prisms represent the first NIR astronomical instrument that uses L-BBH2as the high index material. This material choice was key to the utility of the discovery mode, so significant efforts were put into cryogenic characterization of the material. The final performance of the prism assemblies in their operating environment is described in detail. The spectrograph is going through final alignment, cryogenic cycling, and is being delivered to the Subaru telescope in April 2016. This paper is a report on the laboratory performance of the spectrograph, and its current status in the commissioning process so that observers will better understand the instrument capabilities. We will also discuss the lessons learned during the testing process and their impact on future high-contrast imaging spectrographs for wavefront control.
Document ID
Document Type
Conference Paper
External Source(s)
Groff, Tyler D. (ASRC Federal Space and Defense Greenbelt, MD, United States)
Chilcote, Jeffrey (Toronto Univ. Ontario, Canada)
Kasdin, N. Jeremy (Princeton Univ. Princeton, NJ, United States)
Galvin, Michael (Princeton Univ. Princeton, NJ, United States)
Loomis, Craig (Princeton Univ. Princeton, NJ, United States)
Carr, Michael A. (Princeton Univ. Princeton, NJ, United States)
Brandt, Timothy (Princeton Univ. Princeton, NJ, United States)
Knapp, Gillian (Princeton Univ. Princeton, NJ, United States)
Limbach, Mary Anne (Princeton Univ. Princeton, NJ, United States)
Guyon, Olivier (Subaru Telescope Hilo, HI, United States)
Jovanovic, Nemanja (Subaru Telescope Hilo, HI, United States)
McElwain, Michael W. (NASA Goddard Space Flight Center Greenbelt, MD United States)
Takato, Naruhisa (Subaru Telescope Hilo, HI, United States)
Hayashi, Masahiko (Tokyo Astronomical Observatory Mitaka, Japan)
Date Acquired
July 3, 2017
Publication Date
August 9, 2016
Publication Information
Publication: SPIE Proceedings
Volume: 9908
Subject Category
Report/Patent Number
Meeting Information
Ground-based and Airborne Instrumentation for Astronomy VI(Edinburgh)
Funding Number(s)
Distribution Limits
Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS)