A Sterling Cooler is a highly efficient Cryogenic Cooler. It utilizes the Joule-Thomson effect to cool down a single point on the back of the CMOS. This makes them a form of Joule-Thomson type coolers.
The Joule-Thompson effect is a thermodynamic process that occurs when a fluid expands from high pressure to low pressure at constant enthalpy (an isenthalpic process). This Rapidly Cools the Gas and the surrounding metal of the cooler.
The Tip of the coldest point that goes on the back of the Cooled thermal Sensor is Known as the Cold Finger.
Sterling coolers can also be lined up in stages to Intensify the cooling effect. A Highly efficient single stage stirling cooler can get down to as low as about 40K (depending on ambient) and a dual stage can get down to about 15K or -258.15 degrees C. If insulation is high enough, this effect can be compounded until the >1 Kelvin range.