Zinc Selenide (ZnSE) is the best material for infrared optics. However, the quality of ZnSE in China is very unpredictable.
Gallium Arsenide (GaAs) has a more consistent quality in China as a raw material. However, it is not as good as ZnSe, but it always beats bad bad ZnSe.
There are 2 types of ZnSe.
- CVD ZnSe (Chemical Vapor Deposition) is a process where the environment is maintained in a reactor to promote ZnSe crystal growth.
- PVD ZnSe (Physical Vapor Deposition) is a process where ZnSe scraps are evaporated and then recombine into a solid. PVD ZnSe has legitimate practical purposes, but Co2 laser optics is not one of them.
CVD ZnSe is only made in the USA.