3.4 µm to 660 nm wavelength conversion using Er3+ doped materials

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.