Dewar

SpectroCam's mechanical design is somewhat unusual for a mid-infrared instrument because almost the entire optical bench assembly is cooled with liquid nitrogen. Only the detector itself, its housing, and the filter wheel are cooled to 5 -- 6 K with liquid helium. By pumping a vacuum on the nitrogen and reducing its temperature to about 60 K, the optical bench thermal radiation that reaches the detector is reduced to well below the level entering through the dewar window, even in high-resolution spectrograph mode.

Some important specifications are listed in Table 1.5.

Table 1.5:   SC-10 Cryogenic Specifications
LN2 Capacity 15 liters
LHe Capacity 3 l
LHe Capacity, gaseous equivalent 2400 l
LN2 temperature, pumped 60 K
LN2 hold time 2 - 3 days
LHe hold time, LN2 unpumped 10 - 12 hrs
LHe hold time, LN2 pumped 18 - 24 hrs