Zinc Selenide (ZnSe)
Positive Meniscus Lenses

Meniscus lenses are primarily used for focusing to small spot sizes or collimation applications. They provide significantly superior performance by greatly reducing spherical aberrations. Positive meniscus (convex-concave) lenses, which consist of a convex surface and a concave surface and are thicker in the middle than at the edges & cause light rays to converge, are designed to minimize spherical aberration in optical systems. When used to focus a collimated beam, the convex side of the lens should face the source to minimze spherical aberration. When used in combination with another lens, a positive meniscus lens will shorten the focal length and increase the numerical aperture (NA) of the system without introducing significant spherical aberration. Since a positive meniscus lens has a greater radius of curvature on the concave side of the lens than on the convex side, real images can be formed.

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ZnSe lenses are particularly well suited for use with high-power CO2 lasers. Due to the high refractive index of ZnSe, we can offer the spherical best form design for ZnSe, which is the positive meniscus design. These lenses induce small aberrations, spot sizes, and wavefront errors comparable to best form lenses fabricated by other materials.

Paralight Optics offers Zinc Selenide (ZnSe) Positive Meniscus Lenses available with a broadband AR coating optimized for the 8 µm to 12 μm spectral range deposited on both surfaces. This coating greatly reduces the high surface reflectivity of the substrate, yielding an average transmission in excess of 97% over the entire AR coating range.