Design and fabrication of antireflective optical elements for CO2 lasers

Anti-reflective optical elements prepared on ZnSe substrates are the main optical devices in CO2 lasers. These ‎anti-reflective coatings are used in the far-infrared region at the specified wavelength of 10600 nm. For the preparation phase of these anti-reflective coatings, first, the characterization of the used materials in this wavelength was investigated and then YbF3 and ZnS were chosen. However, a lot of research work has been done in the country to make reflection mirrors of gold and silver for a wavelength of 1.6 microns, but no research has been done on anti-reflective optical window or part of it at this wavelength. Then, anti-reflective coating at 10600 nm was designed by the Macleod software using these two materials. These thin films were deposited on one side of ZnSe substrates by physical vapor deposition (PVD) method with Balzers- Ba510 coating system. Optical element operation was investigated by a 10 W CO2 laser and the transmission was measured for the standard anti-reflection, the polished substrate, and the deposited antireflective element. The results show that the prepared anti-reflective element has 77.84% transmission coefficient. By studying the morphology and thickness of the layers by SEM, it was found that the transmission coefficient of ZnSe substrate is optimized by the prepared anti-reflection element.