@proceedings {3071, title = {Cryogenic near infrared spectropolarimeter for the Daniel K. Inouye Solar Telescope}, volume = {9908}, year = {2016}, month = {09/2016}, pages = {99084D}, publisher = {Proc SPIE}, abstract = {

The Cryogenic Near Infrared Spectropolarimeter (CryoNIRSP) is a first light instruments for the Daniel K Inouye Solar Telescope (DKIST). This dualbeam instrument is designed to sensitively measure the full polarization state (Stokes I, Q, U and V) of solar spectral lines at wavelengths from 1 μm (500 nm goal) to 5 μm. The high dynamic range of the instrument allows measurements of the solar disk, near-limb and faint corona where the near-limb and coronal observations depend on DKIST\’s coronagraphic capabilities. It has the widest field-of-view and longest wavelength coverage of the four first-light DKIST facility instruments. These capabilities will provide sensitive measurements of the solar disk in the carbon monoxide (CO) bands; unique observations of spicules, prominences, flares and eruptive events in the low corona; and unprecedented sensitive measurements of the coronal magnetic field.

The CryoNIRSP instrument is divided into three optical subsystems: the feed optics, the spectrograph and the context imager. The room temperature feed optics directs the light to 1) the spectrograph only 2) the context imager only 3) the spectrograph and context imager simultaneously. It also provides means to scan the field of view across the spectrograph slit, includes calibration lamps and accommodates the polarization modulator.

The spectrograph is an all reflective design to provide high overall throughput and broad spectral coverage. A 408 mm wide R2 echelle grating is required to achieve the desired resolution at the longest wavelengths. In order to reduce the thermal background for the IR observations, we use closed helium cycle cryo-coolers to cool the filters, imaging optics, grating, polarization analyzer and detector to 77 K. The spectrograph will operate in a high resolution (R=100,000) disk mode and a low resolution (R=30,000) coronal mode with spatial resolutions of 0.15 and 0.5 arcsec and fields of view of 1.5 x 1.5 and 4 x 3 arcmin respectively. A multi-slit operation mode is also available that efficiently uses detector pixels for large area single-line spectropolarimetry. The context imager is a separate optical system that records a 100 x 100 arcsec field around the slit at wavelengths of coronal emission lines of interest. The feed optics scan mirror can be used to mosaic the whole coronal mode field of view. The bandpass filters and detector inside the imager are cooled to cryogenic temperatures as well. Both, spectrograph and context imager use a 2048 x 2048 HAWAII 2 array produced by Teledyne Scientific \& Imaging. The PB1HS array controller was developed at the University of Hawaii, Institute for Astronomy in Hilo. This new controller reads the H2RG in slow and fast mode and allows for external triggering which is essential for synchronization to the polarization modulator.

CryoNIRSP has been fully assembled and initial laboratory tests were performed. This paper discusses the CryoNIRSP design and lessons learned during cryo-mechanical, grating rotation stage, and polarization analyzer sub-assembly testing.

}, author = {Fehlmann, Andre and Giebink, Cynthia and Jeff R. Kuhn and Messersmith, Ernesto J and Don Mickey and Isabelle Scholl and James, Don and Hnat, Kirby and Schickling, Greg and Schickling, Richard} }