• ZnSe Negative-Meniscus-Lens

Zinc Selenide
Negative 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. Negative meniscus (convex-concave) lenses , which consist of a convex surface and a concave surface and are thinner in the middle than at the edges & cause light rays to diverge, are designed to minimize spherical aberration in optical systems.

When used to diverge light in beam expanding applications, the concave surface should face the beam to minimize spherical aberration. When used in combination with another lens, a negative meniscus lens will increase the focal length and decrease the numerical aperture (NA) of the system.

ZnSe lenses are ideal for CO2 lasers application due to excellent imaging characteristics and high resistance to thermal shock. Paralight Optics offers Zinc Selenide (ZnSe) negative meniscus lenses, these lenses decrease the NA of an optical system and are available with a broadband anti-reflection coating, which is optimized for the 8 µm to 12 μm spectral range deposited on both surfaces and yields an average transmission in excess of 97% over the entire AR coating range.




Zinc Selenide (ZnSe)

Coating Option:

Uncoated or with Antireflection Coatings

Focal Lengths:

Available from -40 to -1000 mm


To Decrease the NA of an Optical System


Common Specifications:


Reference Drawing for

Negative 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

    Negative Meniscus Lens

  • Index of Refraction

    2.403 @10.6 µm

  • Abbe Number (Vd)

    Not defined

  • Thermal Expansion Coefficient (CTE)

    7.1x10-6/℃ at 273K

  • 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 < 1.5%

  • Transmission over Coating Range (@ 0° AOI)

    Tavg > 97%

  • Design Wavelength

    10.6 μm

  • Laser Damage Threshold (Pulsed)

    5 J/cm2 (100 ns, 1 Hz, @10.6μm)



♦ Transmission curve of 5 mm thick, uncoated ZnSe substrate: high transmission from 0.16 µm to 16 μm
♦ Transmission curve of 5 mm thick AR-coated ZnSe Window: Tavg > 97% over the 8 µm - 12 μm range


Transmission Curve of 5mm AR-Coated (8 µm - 12 μm) ZnSe Window

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