Joule-Thomson cryostat cooled infrared cell having a built-in thermostat sensing element

Claim 1

A cryogenic infrared energy sensing unit having a built-in Joule-Thomson cryogenic cooler of the type utilizing exhaust refrigerant gas to regeneratively cool the refrigerant supply line and having a built-in thermostat sensing element for providing an electrical signal to control operation of the cooler, in combination, comprising, a. a double walled, Dewar type thermal insulation casing having a closed and an open end, the interior of the casing forming an elongated central cryostat chamber, the closed end of the thermal insulation casing forming the front end of the unit and containing an infrared sensor element affixed to the interior surface of the inner wall of the double walled casing, the outer wall of the casing at the front end being formed of an infrared energy window material, b. a cryostat assembly shaped for insertion in the cryostat chamber and adapted to cool the exterior surface of the inner wall of the double walled casing at the front end, said cryostat assembly comprising a two-piece mandrel consisting of a rear thin walled tubular member and metallic heat exchange front end tip member plugging the front end of the tabular member, and a refrigerant supply tube helically wrapped around the two-piece mandrel terminating at its forward direction with an open end to form the gas expansion nozzle to provide the Joule-Thomson cooling effect, the construction being such that the helically coiled refrigerant is supported between the tubular member of the two-piece mandrel and the wall of the cryostat chamber in a manner permitting counterflow of the exhaust gases from the front to rear end of the cryostat chamber about the helical tubing in the annular space between the mandrel and the lateral wall of the cryostat chamber, c. a temperature responsive variable impedance element made of an impurity doped semi-conductor material which intrinsically exhibits temperature sensitive characteristics at the cryogenic temperature region desired for operation of the infrared sensor element, said variable impedance element being disposed in the interior of the tubular mandrel element and affixed by one of its sides to rear face of the heat exchange front end tip member, and d. means forming a pair of output connections across the variable impedance element and accessible from the exterior of the unit.