  We introduce the Michigan Infrared Test Thermal ELT N-band (MITTEN) Cryostat,
a new facility for testing infrared detectors with a focus on mid-infrared
(MIR) wavelengths (8-13 microns). New generations of large format, deep well,
fast readout MIR detectors are now becoming available to the astronomical
community. As one example, Teledyne Imaging Sensors (TIS) has introduced a
long-wave Mercury-Cadmium-Telluride (MCT) array, GeoSnap, with high quantum
efficiency (> 65 %) and improved noise properties compared to previous
generation Si:As blocked impurity band (BIB) detectors. GeoSnap promises
improved sensitivities, and efficiencies, for future background-limited MIR
instruments, in particular with future extremely large telescopes (ELTs). We
describe our new test facility suitable for measuring characteristics of these
detectors, such as read noise, dark current, linearity, gain, pixel
operability, quantum efficiency, and point source imaging performance relative
to a background scene, as well as multiple point sources of differing contrast.
MITTEN has an internal light source, and soon an accompanying filter wheel and
aperture plate, reimaged onto the detector using an Offner relay. The baseline
temperature of the cryostat interior is maintained < 40 K and the optical bench
maintains a temperature of 16 K using a two-stage pulse-tube cryocooler package
from Cryomech. No measurable background radiation from the cryostat interior
has yet been detected.
