Energy conversion from 3.3 μm to 660 nm in rare earth-doped materials for all optical gas sensing

The 2-15 μm spectral range hosts many optical sensing applications from biology to environmental monitoring, and infrared spectroscopy is a simple and reliable way to provide fast and in-situ analysis method. Rare-earth ion emissions within chalcogenide glasses with low phonon energies proved to be efficient to address mid-IR luminescence based sensing applications. In particular, they give promising results for the development of all-optical gas sensors in the 3 to 5 μm spectral range based on IR conversion into visible light using rare earth excited state absorption mechanisms. In this article, we report the wavelength conversion of 3.4 μm radiation into 660 nm in Er3+:KPb2Cl5 bulk crystal, Er3+:Ga5Ge20Sb10S65 and Er3+:Ga5Ge20Sb5S70 glasses using an excited state absorption process. This wavelength conversion is the result of the excitation of Er3+ ions following the excited state absorption of IR photons and the Er3+ ions subsequent spontaneous emission in the visible domain. Using an 808 nm pumping, a 3.4 μm photon excited state absorption gives rise to a 660 nm emission. This wavelength conversion device can be further implemented for methane all-optical sensing at 3.4 μm, for the development of remote “all-optical” methane mid-IR sensors with only visible and near-IR input and output signals. This “all-optical concept” enables the use of silica fibers over large distances, thus considerably increasing the scope of possible applications.