New Regimes of Excitation and Mid-IR Lasing of Transition Metal Doped II–VI Crystals

Recent progress in transition-metal doped II–VI semiconductor materials (mainly Cr²⁺:ZnSe and ZnS) make them the laser sources of choice when one needs a compact system with continuous tunability over 2–3.1 μm, output powers up to 2W, and high (up to 70%) conversion efficiency. The unique combination of technological (low-cost ceramic material) and spectroscopic characteristics (ultrabroadband gain bandwidth, high óproduct and high absorption coefficients) make these materials ideal candidates for “non-traditional” regimes of operation such as microchip and multi-line lasing. This chapter reviews these non-traditional Cr-doped mid-IR lasers as well as describes emerging Fe²⁺:ZnSe lasers having the potential to operate at room temperature over the spectral range extended to 3.7–5.1 μm. In addition to effective RT mid-IR lasing transition-metal doped II–VI media, being wide band semiconductors, hold the potential for direct electrical excitation. This work shows the initial steps toward achieving this goal by studying Cr²⁺ ion excitation into the upper laser state 5E via photoionization transitions as well as via direct electrical excitation.

Keywords: Transition-metal doped II–VI; Cr²⁺:ZnSe; Fe²⁺:ZnSe; tunable mid-infrared lasers; photoluminescence; electroluminescence; photo-conductance.