Spherical lenses are normally used to focus laser beams. The shorter the focal length, the stronger the influence of the spherical aberration. Light rays that pass through the lens do not have the same focal length; thus, the focal point “drifts.”
Aspherical lenses with at least one free-form surface produced using CNC polishing techniques (diamond turning) help. Ideally, aspherical lenses replace a system of several spherical lenses, thereby reducing weight and losses through surface scattering. Aspherical optics in the FIR range are required for industrial applications and the aerospace and defense industries.
LASER COMPONENTS offers these components with a diameter of up to 400 mm in the following materials: ZnSe, Ge, Si, CaF2, Cu, Al, or CleartranTM for thermal imaging.
For a substrate with a diameter of 150 mm, the shape deviation is a ½ fringe and the surface roughness is < 30 Å RMS.
The aspheres can be coated according to customer request for all wavelengths from 2 μm to 16 μm. For use with CO2 lasers, they are usually equipped with an AR coating for 10.6 μm or 9.3 μm; this has a low absorption and is suited for high-power applications.
More Information: http://www.lasercomponents.com/lc/product/znse-lenses-for-co2-lasers/