• ZnSe-Positive-Meniscus-Lens

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.

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.




Zinc Selenide (ZnSe)

Coating Option:

Uncoated or with Antireflection Coatings for the 8 - 12 μm

Focal Lengths:

Available from 15 to 200 mm


To Increase the NA of an Optical System


Common Specifications:


Reference Drawing for

Positive Meniscus Lens

f: Focal Length
fb: Back Focal Length
R: Radius of Curvature
tc: Center Thickness
te: Edge Thickness
H”: Back Principal Plane

Note: The focal length is determined from the back principal plane, which does not necessarily line up with the edge thickness.



Ranges & Tolerances

  • Substrate Material

    Laser-Grade Zinc Selenide (ZnSe)

  • Type

    Positive Meniscus Lens

  • Index of Refraction (nd)


  • Abbe Number (Vd)

    Not defined

  • Thermal Expansion Coefficient (CTE)

    7.1 x 10-6/℃

  • Diameter Tolerance

    Precison: +0.00/-0.10mm | High Precision: +0.00/-0.02mm

  • Center Thickness Tolerance

    Precison: +/-0.10 mm | High Precision: +/-0.02 mm

  • Focal Length Tolerance

    +/- 1%

  • Surface Quality (Scratch-Dig)

    Precison: 60-40 | High Precision: 40-20

  • Spherical Surface Power

    3 λ/4

  • Surface Irregularity (Peak to Valley)


  • Centration

    Precison: < 3 arcmin | High Precision: < 30 arcsec

  • Clear Aperture

    80% of Diameter

  • AR Coating Range

    8 - 12 μm

  • Reflectance over Coating Range (@ 0° AOI)

    Ravg < 1.0%, Rabs < 2.0%

  • Transmission over Coating Range (@ 0° AOI)

    Tavg > 97%, Tabs > 92%

  • Design Wavelength

    10.6 μm

  • Laser Damage Threshold (Pulsed)

    5 J/cm2 (100 ns, 1 Hz, @10.6μm)



♦ Transmission curve of 10 mm thick, uncoated ZnSe substrate: high transmission from 0.16 µm to 16 μm
♦ Transmission curve of 5 mm thick AR-coated ZnSe lens: Tavg > 97%, Tabs > 92%over the 8 µm - 12 μm range, the transmission in the out-of- band regions is fluctuating or sloped


Transmission Curve of 5mm Thick AR-coated (8 - 12 μm) ZnSe lens at 0° AOI