Clear aperture cryostat for an infrared detector

Claim 2

An infrared sensitive device embodying an up-convertor having a receiving surface for receiving an infrared image and an emitting surface for emitting a corresponding image at a pre- selected wavelength, and cooling means for the up-convertor, said cooling means comprising: at least one heat sink for attaching to and covering at least one surface of the up-convertor for conducting heat away from the up-convertor, said heat sink being substantially transparent to radiation at either infrared or said pre-selected wavelength dependent upon whether said heat sink is attached to said receiving or said emitting surface respectively; and cryostat means for cooling the heat sink, said cryostat means operating on a Joule-Thomson effect and being located so that it does not intercept either the received or emitted images.

Claim 3

An infrared sensitive device according to claim 1 wherein the cryostat means comprises: means providing an expansion chamber in a heat exchange relationship with the heat sink for cooling the heat sink, and gas flow conducting means including; input means comprising: an input channel for conducting gas to the chamber; an inlet at one end of the input channel for connection to a source of high pressure gas; and a throttling device at the other end of the input channel and located in a wall of the chamber for directing the gas into the chamber; and exhaust means comprising; an exhaust channel for conducting gas from the chamber; an outlet at one end of the exhaust channel for allowing for the exhaust gas to exit; and a throttling device at the other end of the exhaust channel and located in a wall of the chamber for directing gas from the chamber into the exhaust channel.

Claim 4

An infrared device according to claim 2 wherein the input channel is a helical capillary channel and wherein the exhaust channel is a concentric helical capillary channel immediately adjacent to the input channel and in a heat exchange relationship with the input channel for regeneratively cooling the input gas.

Claim 5

An infrared device according to claim 3 wherein the cryostat is located immediately adjacent to the path of light.

Claim 6

An infrared sensitive device according to claims 1,2,3 or 4 wherein the heat sink is comprised of magnesium fluoride (MgF2).

Claim 7

An infrared sensitive device according to claims 1, 2, 3, or 4 wherein the heat sink is comprised of zinc selenide (ZnSe).