• ZnSe-DCX-1

Zinc Selenide (ZnSe)
Bi-Convex Lenses

Bi-Convex or Double-Convex (DCX) Spherical Lenses are spherical and have an identical curvature on both sides of the lens, so they are symmetric and have a positive focal length. At unit conjugation, coma and distortion cancel out due to the symmetry. These lenses can be used to focus incoming light and are popular for many finite imaging applications.

Though Bi-convex lenses minimize aberrations in situations where the object and image distances are equal or nearly equal, when deciding between a bi-convex or DCX lens and a plano-convex lens, both of which cause collimated incident light to converge, it is usually preferable to choose a bi-convex lens for minimizing aberrations if the ratio of the object and image distances (the absolute conjugate ratio) is between 5:1 and 1:5. Outside this range, plano-convex lenses are usually preferred.

ZnSe lenses are particularly well suited for use with high-power CO2 lasers. Paralight Optics offers Zinc Selenide (ZnSe) Bi-Convex Lenses available with a broadband AR coating optimized for the 8 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. Check the following Graphs for your references.




Zinc Selenide (ZnSe)


Broadband AR coating for the 8 - 12 µm Range

Focal Lengths:

Available from 15 to 200 mm


Ideal for CO2 laser Applications


Common Specifications:


Reference Drawing for

Double-convex (DCX) Lens

Dia: Diameter
f: Focal Length
ff: Front 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

    Double-Convex (DCX) Lens

  • Index of Refraction @10.6 µm


  • Abbe Number (Vd)

    Not defined

  • Thermal Expansion Coefficient (CTE)

    7.1x10-6/℃ at 273K

  • Diameter Tolerance

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

  • Thickness Tolerance

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

  • Focal Length Tolerance


  • Surface Quality (scratch-dig)

    Presicion: 60-40 | High Precison: 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

    >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 Bi-Convex: Tavg > 97% over the 8 µm - 12 μm range, the transmission values in out-of-band regions is only for references


Transmission Curve of AR-coated (8 - 12 μm) ZnSe Bi-Convex Lens