TABLE OF CONTENTS Cryogenic engineering is important throughout the realm of electro-optics, as detectors, filters, and sometimes optics require cooling for high sensitivity especially for infrared cameras and instruments. Therefore, it can be said that cryocooling is a key enabling technology for modern sensors. Many systems require some form of refrigeration to very low temperatures, at least for some components. Most commonly, the coldest part of the system, other than the dewar, is the detector array.
Usually, this cooling is accomplished by employing one of several methods, including
A liquid reservoir of cryogen (typically, for end-use temperatures of less than 100 K).
A mechanical refrigerator (for end-use temperatures from 4 to 220 K).
A Joule Thomson (JT) blow-down expander (typically, for end-use temperatures from 20 to 110 K). Several types of JT systems are in use those with mechanical pumps to create the desired pressures, those that use hydrated bed sorption technology to create the desired pressures, and those that use stored gas.
A thermoelectric cooler (for end-use temperatures above about 180 K).
The cooling is usually delivered to the focal plane, filter, cold shield, surrounding surfaces [e.g., the focal plane array (FPA) mux and carrier], and sometimes the optics. Typically, an infrared detector focal plane array will require cooling, as will its immediate surroundings. All of these parts are contained in a super-Thermos bottle called a dewar, the only exception being some space sensors. For high sensitivity at long wavelengths, cooling is also required for portions of the telescope structure and optics.
Cryogenic...
