Features

• Ø1" CVD Laser-Grade ZnSe Substrate
• 2 AR Coating Options: 3 - 5 µm or 8 - 12 µm
• 3 Focal Lengths Available: 12.7, 25, or 50 mm
• Diffraction-Limited Performance (f = 25 and 50 mm)
• Near Diffraction-Limited Performance (f = 12.7 mm)

An expansion of Thorlabs' IR product line, Thorlabs' Ø1" Zinc Selenide (ZnSe) Aspheric Lenses offer high transmission over the broad spectral range from 0.6 - 16 μm and are available with one of two broadband AR coatings to minimize surface reflection losses: -E for the 3 - 5 µm range or -F for the 8 - 12 µm range. These coatings greatly reduce the high surface reflectivity of the substrate, yielding an average reflectance of less than 1.15% over the entire AR coating range. See the Graphs tab for detailed information.

ZnSe lenses are typically used as collimators for laser applications in the 0.6 - 16.0 μm spectral region, such as biomedical and military applications. When used for colliimation, the plano surface should face the laser diode or other point source for best performance. With a higher index (~2.4), ZnSe aspheres can be designed with shorter focal lengths and lower dispersion than comparable aspheres made from other materials, such as CaF₂. Due to the low absorption coefficient of ZnSe, these lenses, particularly with the -F coating, are also well suited for use with high-power CO₂ lasers.

These lenses are manufactured using diamond turning machines and are tested using a surface profilometer to ensure the correct aspheric profile. As a result, these aspheric lenses offer RMS wavefront errors that are typically 20 to 50 times less than similarly sized molded aspheric lenses.

In contrast to their plano-convex counterparts, these ZnSe aspheric lenses focus or collimate light without introducing spherical aberration into the transmitted wavefront. For monochromatic sources, spherical aberration is often what prevents a single spherical lens from achieving diffraction limited performance when focusing or collimating light. Thus, an aspheric lens is often the best single element solution for many applications including collimating the output of a fiber or laser diode, coupling light into a fiber, spatial filtering, or imaging light onto a detector.

ZnSe Transmission Data

The transmission curve below was obtained using a 6.3 mm thick, uncoated sample of ZnSe; the incident light was normal to the surface. Please note that this is the measured transmission, including surface reflections.

The transmission curve below shows significant losses throughout the usable range due to surface reflections. These reflections are caused by the high index of refraction (2.4 at 10.6 μm) of ZnSe. Because of this, anti-reflection coatings (shown below Transmission plot) should always be used on ZnSe optics.

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ZnSe Reflectance Data

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The plots above show the reflectance of AR-Coated ZnSe Aspheric lenses.

Aspheric Lens Formula

Aspheric Coefficients