Lens
Zinc Selenide (ZnSe), is a lemon-yellow to orange-colored material with a low absorption coefficient of up to 0.0005 at the CO2 laser wavelength of 10,600 nm, and transparent across a wide spectral range from visible to infrared, allowing for the quick tuning of optical systems using visible spectra emitters. However, if overheated, it can crack.
Zinc selenide is used in the production of optical lenses for carbon dioxide (CO2) lasers. The lenses are installed in the head of the laser engraver with their convex side upwards — towards the emitter. Tighten the laser head retaining ring gently to prevent the lens from bursting. During operation, the lenses must be kept clean, the products of material combustion must be removed with compressed air, dust and soot should be blown off, or in the case of severe fouling, gently wiped with a lint cloth moistened with isopropyl alcohol to avoid scratching.
Due to their lower refractive index than that of gallium arsenide (GaAs), zinc selenide lenses have an increased focal depth, which allows cutting through thicker materials without violating the straight geometry of the cut, however, when performing engraving in cases where there are surface height difference, the diameter of the focal spot will be slightly larger than that of gallium arsenide lenses, so this may be unacceptable for very fine engraving.
Lenses with focal lengths of 1.5 to 2 inches (short-focus lenses) are generally used primarily for engraving and cutting thin materials up to 2 mm thick
Lenses with a focal length of 2.5 inches are considered versatile and are used equally for engraving and cutting materials up to 3 mm thick
Lenses with a focal length of 3 inches or more (long focal length lenses) are used primarily for cutting thicker materials to maintain a straight cut geometry, but are rarely used for engraving, except where there are significant variations in the surface height.