ZnSe lenses for CO2 lasers

CO2 lasers emit at wavelengths between 9 and 11 µm - typically at 9.36 µm or 10.6 µm. The spectrum is far above the wavelengths used for conventional laser material processing.

Radiation in the LWIR range poses challenges for optical designers who develop and manufacture the focusing scan lens and the upstream beam expander, as only a few glasses are transparent in this spectral range. As the transmission curves show, germanium (Ge), zinc selenide (ZnSe) and zinc sulphide (ZnS) are among the infrared-suitable glasses that can be partially used for CO2 lasers. ZnSe is often preferred to Ge due to its higher temperature resistance. ZnS offers a few advantages over ZnSe, such as transparency in the visible range or easier processing. However, it is unsuitable for lasers with medium or high power at 10.6 µm because the absorption coefficient at this wavelength is too high in contrast to ZnSe.

Special coatings can increase the transmission of ZnSe by around 20 percentage points and ensure that less energy remains in the lens, thereby decreasing the temperature and increasing efficiency.

The Sill Optics team is able to design and manufacture lenses for CO2 laser usage. Since these types of lenses are still niche products, they are not listed in the catalog and can be requested as a custom product. We look forward to supporting you in setting up your CO2 laser system.