  CYRA (CrYogenic solar spectrogRAph) is a facility instrument of the 1.6-meter
Goode Solar Telescope (GST) at the Big Bear Solar Observatory (BBSO). CYRA
focuses on the study of the near-infrared solar spectrum between 1 and 5
microns, a under explored region which is not only a fertile ground for
photospheric magnetic diagnostics, but also allows a unique window into the
chromosphere lying atop the photosphere. CYRA is the first ever fully cryogenic
spectrograph in any solar observatory with its two predecessors, on the
McMath-Pierce and Mees Telescopes, being based on warm optics except for the
detectors and order sorting filters. CYRA is used to probe magnetic fields in
various solar features and the quiet photosphere. CYRA measurements will allow
new and better 3D extrapolations of the solar magnetic field and will provide
more accurate boundary conditions for solar activity models. Superior spectral
resolution of 150,000 and better allows enhanced observations of the
chromosphere in the carbon monoxide (CO) spectral bands and will yield a better
understanding of energy transport in the solar atmosphere. CYRA is divided into
two optical sub-systems: The Fore-Optics Module and the Spectrograph. The
Spectrograph is the heart of the instrument and contains the IR detector,
grating, slits, filters, and imaging optics all in a cryogenically cooled Dewar
(cryostat). The detector a 2048 by 2048 pixel HAWAII 2 array produced by
Teledyne Scientific & Imaging, LLC. The interior of the cryostat and the
readout electronics are maintained at 90 Kelvin by helium refrigerant based
cryo-coolers, while the IR array is cooled to 30 Kelvin. The Fore-Optics Module
de-rotates and stabilizes the solar image, provides scanning capabilities, and
transfers the GST image to the Spectrograph. CYRA has been installed and is
undergoing its commissioning phase.
