Abstract
Spectroscopic characterization of Fe:ZnSe(Cr:ZnSe) crystals under visible excitation into the charge transfer bands of Transition Metal ions were studied. The excitation efficiencies of mid-IR photoluminescence between (5)T(2)((5)E) and (5)E((5)T(2)) states via direct relaxation to the upper laser levels and via metastable upper (3)T(1) were investigated. It was demonstrated that the latter route is the dominant process for Cr(2+) ions and could provide sufficient pump rate for mid-IR lasing. The pump efficiencies via direct relaxation to the upper laser levels were estimated to be <2% for both ions under 532 nm excitation wavelength.
Highlights
Tunable middle infrared lasers are promising for a broad range of applications such as medical diagnosis, remote sensing, and optical communication
Within this class of lasers, the transition metal (TM) doped II-VI (e.g. ZnSe and ZnS) crystals are arguably gain media of choice for the development of broadly tunable laser systems operating at room temperature (RT) over the 2-6 μm spectral range [1,2,3,4]
While there is some quenching of the lifetime at room temperature, the lifetime remains at the level of several μs and is sufficient to obtain lasing in the Continuous wave (CW) operational regime
Summary
Tunable middle infrared (mid-IR) lasers are promising for a broad range of applications such as medical diagnosis, remote sensing, and optical communication Within this class of lasers, the transition metal (TM) doped (e.g. chromium and iron) II-VI (e.g. ZnSe and ZnS) crystals are arguably gain media of choice for the development of broadly tunable laser systems operating at room temperature (RT) over the 2-6 μm spectral range [1,2,3,4]. Fe2+:II-VI exhibits no excited state absorption and lasing has been demonstrated in all regimes of operation over the 3.5-6 μm spectral range with CW power of 1.6 W and pulse energies 2.1 J in free running, and 30 mJ in the gain-switched regime [1]. An understanding of the relaxation process under visible excitation in Cr2+ and Fe2+ ZnSe/ZnS crystals cannot only provide an alternative pumping method in the form of optical excitation, and a better understanding of processes that could lead to the development of a new type of solid-state lasers with electrical pumping
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