Broadband multilayer antireflection coating for quantum cascade laser facets

We demonstrate a broadband multilayer anti-reflection (AR) coating applied to a quantum cascade laser (QCL) facet. The bandwidth of the AR coating was optimized for the range of 8.0 to 12.0 mu m to cover the entire emission spectrum of a broad-gain QCL. The laser facets are high-reflectance and AR-coated for use in an external cavity QCL The AR coating is composed of layers of yttrium fluoride, zinc sulfide, and germanium, all deposited using electron-beam evaporation, and the modal reflectance of the laser facet across the wavelength range was reduced to 0.75%. The external cavity laser performance in a Littrow-type configuration is also described. (C) 2018 Optical Society of America