What is an immersion lens and how do they impact measurement of IR radiation?
Optical immersion is achieved by using high refractive index microlenses in order to improve performance of the devices but may limit acceptance angle. Optical immersion is a monolithic integration of a detector element with hyperhemispherical microlens (basic configuration) that makes optical linear size of detector 11 times larger compared to its physical size. This results an improvement of D* by one order of magnitude and electric capacitance by a factor of two orders of magnitude less compared to a conventional detector of the same optical area. We are glad to help you further to determine if you’re not sure if you should use an immersion lens in your system or not.
Source (with permission to reproduce): https://vigo.com.pl/en/support/faq/