Cryogenic Near Infrared Spectropolarimeter for the Daniel K. Inouye Solar Telescope

The Cryogenic Near Infrared Spectropolarimeter for the Daniel K Inouye Solar Telescope is designed to measure polarized light from 0.5 to 5 mu m. It uses an almost all reflective design for high throughput and an R2 echelle grating to achieve the required resolution of up to R = 100,000. The optics cooled to cryogenic temperatures reduce the thermal background allowing for IR observations of the faint solar corona. Both the spectrograph and its context imager use H2RG detector arrays with a newly designed controller to allow synchronized exposures at frame rates up to 10 Hz. All hardware has been built and tested and the key components met their design goals. 1) The cryogenic system uses mechanical closed cycle coolers which introduce vibrations. Our design uses a two stage approach with a floating mounting disk and flexible cold links to reduce these. The vibration amplitudes on all critical stages were measured and are smaller than 1 pm. 2) The grating stage of the spectrograph uses a double stack of harmonic drives and an optical encoder to provide sub-arcsecond resolution and a measured repeatability of better than 0.5 arcsec.