Optical Coatings as Active Media for Mid-Infrared lasers

Optical Coatings as Active Media for Mid-infrared Lasers Abstract: Thin films of Cr-doped ZnS with high infrared transparency have been deposited by molecular beam epitaxy and show optical properties suitable for use as active media in mid-infrared laser applications.. OCIS codes: (310.6860) Thin films, optical properties; (310.6870) Thin films, other properties (160.3380) Laser materials 1. Introduction Mid-infrared spectroscopy is an expanding field with biomedical and environmental monitoring applications. Miniaturization of the sources would dramatically improve the deployment and societal benefits of the sources needed, but to date, only bulk gain materials [1,2] have been used. In recent work, laser modification of a bulk crystal was used to define a waveguide within a bulk crystal [3]. However, there has been progress in the use of polycrystalline and ceramic [4–6] materials for lasing, which suggests that thin film material of sufficient quality for the production of channel waveguide devices is possible. Some progress has been made with pulsed laser deposition and molecular beam evaporation of TM doped films [7,8], but the material quality has not been optimal. In this paper, we present thin films of Cr-doped ZnS -- materials that are commercially available in bulk crystals for optical applications--and show that the thin films have fluorescence and absorption properties that make them excellent candidates for development into waveguide lasers for the mid-IR 2. Film growth and characterization Films were deposited using an electron-beam source for the metal, and a Knudsen cell for the ZnS, onto sapphire, CaF2 and silicon substrates, at a base pressure