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 µm 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.

External-cavity quantum cascade laser using intra-cavity out-coupling.

We describe an external-cavity quantum cascade laser with an intra-cavity out-coupling optical system, tunable from 8.4 µm to 10.8 µm. The new optical configuration allows higher output power compared to a conventional Littrow-type external cavity approach, while keeping the broad tunability of wavelength. We achieved 1 W output power at the maximum in pulse-mode operation, which is more than twice the optical power using the Littrow design with the same gain chip.

Broadband multilayer anti-reflection coating for mid-infrared range from 7 µm to 12 µm.

We describe a design concept for broadband anti-reflection coatings for the mid-infrared that allows thinner film thickness and characterize its properties in the mid-infrared range from 7 µm to 12 µm. Two demonstrator coatings comprising zinc sulfide, yttrium fluoride, and germanium, all of which are deposited by electron beam evaporation on indium phosphide substrates, are optimized for the 7-12 µm and the 10-12 µm ranges. They exhibit less than 1.0% reflection over the target wavelength ranges with notably thin coating thickness.