What are the types of optical lenses and their characteristics?

Germanium is a commonly used infrared optical material with high hardness, good thermal conductivity, and water solubility, its transmission spectrum range is 2-12 μ m, the single crystal germanium has good mechanical and thermal conductivity, which has very small absorption at 10.6um, making it an ideal material for CO2 laser lenses, windows, and output coupler.

Zinc Selenide (ZnSe) Meniscus Lenses are meniscus lenses based on zinc selenide.

A meniscus lens has an outer convex mirror surface and an inner concave mirror surface. If the convex curvature is greater than the concave curvature, the lens has a positive focal length. When used in combination with another lens, a positive meniscus lens can shorten the focal length, thereby increasing the numerical aperture of the system without introducing significant spherical aberration. (NA); if the curvature on the concave side is large and the curvature on the convex side is small, it is a negative meniscus lens. 

Zinc selenide is a commonly used optical glass material in the infrared band. The transmission band is 600nm-16μm. It has the characteristics of low absorption and thermal shock resistance. It is often used in thermal imaging systems and can also be used in some visible light optical systems. As the substrate for a variety of optical components, such as lenses, windows, etc.