How do we get things *really* cold?

Question

So like refrigerators and freezers and things like that use the Carnot Cycle. And I understand how that cools things down. But I’ve also heard that with conventional methods the biggest temperature difference you can make is about 100⁰C. So how do we get something like liquid nitrogen at -195⁰C? Are we putting a freezer inside a freezer inside a freezer? Or how do we get stuff that cold?

In: 2

Answer 1

There are alternate architectures like Stirling engines, which can get down to -200 deg C in a single stage. They’re commonly used in things like infrared detectors, where you have to cool the detectors down to liquid nitrogen-like temps to reduce noise.

https://en.wikipedia.org/wiki/Applications_of_the_Stirling_engine#Stirling_cryocoolers