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Recent progress in chromium and iron doped II-VI semiconductor materials makes them the laser sources of choice when one needs a compact system with tunability over 1.9-5.1 μm. Output powers exceeding 10 W and efficiency up to 70% were demonstrated in several Cr doped semiconductors. The unique combination of technological (low-cost ceramic material) and spectroscopic characteristics makes these materials ideal candidates for mid-IR tunable laser systems. This article reviews transition metal doped II-VI materials and recent progress in Cr-and Fe-doped solid-state mid-IR lasers.Critical areas driving future progress in Cr-and Fe-doped chalcogenide middle infrared lasers: fabrication of binary and ternary II-VI ceramic gain media with low phonon cut-off, low optical losses and high design flexibility; high performance laser design with improved characteristics in power (power scaling to dozens of Watts), spectral (spectral coverage over 1.8-6 μm), temporal (frequency comb generation), and pump domains (electrically pumped Cr-and Fe-doped II-VI quantum confined structures).

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Efficient continuous-wave (cw) lasing of Cr(2+):ZnS and Cr(2+):ZnSe crystals in external hemispherical cavities and in a microchip configuration under Er-fiber-laser pumping at room temperature are reported. The key result is what is believed to be the first successful demonstration of cw Cr(2+):ZnS and Cr(2+):ZnSe microchip lasers with maximum output powers of 63 and 100 mW at 2320 and 2520 nm, with slope efficiencies of 53% and 20%, respectively.

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Femtosecond laser sources and optical frequency combs in the molecular fingerprint region of the electromagnetic spectrum are crucial for a plethora of applications in natural and life sciences. Here we introduce Cr 2-based lasers as a convenient means for producing super-octave mid-IR electromagnetic transients via optical rectification (or intra-pulse difference frequency generation, IDFG). We demonstrate that a relatively long, 2.5 μm, central wavelength of a few-cycle Cr 2 :ZnS driving source (20 fs pulse duration, 6 W average power, 78 MHz repetition rate) enabled the use of highly nonlinear ZnGeP 2 crystal for IDFG with exceptionally high conversion efficiency (>3%) and output power of 0.15 W, with the spectral span of 5.8-12.5 μm. Even broader spectrum was achieved in GaSe crystal: 4.3-16.6 μm for type I and 5.8-17.6 μm for type II phase matching. The results highlight the potential of this architecture for ultrafast spectroscopy and generation of broadband frequency combs in the longwave infrared.