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We report on the spectroscopic characterization, absorption saturation, and excited-state dynamics of GR1 centers in synthetic diamonds. The non-linear optical measurements reveal an efficient bleaching of the GR1 center’s ground level under ns-pulsed 633 nm excitation. The maxima of absorption and emission cross sections were estimated to be 4.5 × 10−17 cm2 and 9 × 10−17 cm2 at 630 nm and 780 nm, respectively. The radiative lifetime of the excited level was estimated to be 8.5 ns. The 658 nm probe kinetics uncovered relaxation of 1T2 excited level going predominantly to a metastable state with a lifetime of 220 μs. An induced absorption detected with the use of a highly concentrated diamond sample could be due to up-conversion and photoionization processes in additional impurity-vacancy center with absorption at the short-wavelength tail of GR1. The results presented here indicate that synthetic diamonds with GR1 centers could serve as near infrared gain media or passive Q-switchers for laser cavities over the 633–750 nm spectral range. Optimization of the center concentration and the crystal parameters are required to minimize the induced absorption at the lasing wavelengths.

We report the first room temperature gain-switched Fe:ZnSe hot-pressed ceramic laser pumped by 2.94 µm radiation of mechanically Q-switched Er:YAG laser. The maximum output energy at 4.2 µm was 41 mJ at 3 Hz repetition rate and 120 ns pulse duration. The measured slope efficiency was 25% with respect to the absorbed energy. This technique could be attractive for the future development of high-energy short-pulse solid-state mid-IR systems.

Middle-infrared luminescence of bulk Al:Cr:ZnSe crystal under direct electrical excitation of Cr2+,5E− 5T2 transition, is reported. Effective cross-section of electrical excitation was estimated based on comparative luminescence measurements under electrical and optical (1560 nm) excitations. Calculation of the threshold current density for lasing under electrical excitation of this material was also performed.

We demonstrate the generation of a supercontinuum spanning more than 1.5 octaves over the 1.2–3.7 µm range in a silicon nitride waveguide using sub-40-fs pulses at 2.35 µm generated by a 75 MHz Kerr-lens mode-locked Cr:ZnS laser.

We report on the characterization of energy transfer in iron-chromium co-doped ZnSe middle-infrared laser crystals. The room temperature kinetics of the Fe:Cr:ZnSe sample under excitation of chromium ion at 1560 nm shows that energy transfer in Fe-Cr centers could be as fast as 290 ns. This rate is close to the non-radiative relaxation rate of Fe2+ ions in this host. The analysis of energy transfer rate in Cr-Cr; Fe-Fe and Cr-Fe pairs based on the resonance dipole-dipole interaction showed that energy transfer rate could be as fast as 109 s-1.

We report on the spectroscopic and laser characterization of negatively charged nitrogen-vacancy (NV−) centers in diamond. Spectroscopic properties such as absorption and emission spectra as well as kinetics were studied, and parameters such as cross-sections and lifetimes were estimated. A vibronic band of NV0 with zero phonon line (ZPL) at 575 nm was detected under 532 nm pulsed excitation due to the photoionization of NV−. Transmission of 532 nm pump pulses saturate around ∼10%, which is much smaller than the theoretical level. Δk/k0 kinetics revealed slow recovery of NV− centers after photoionization under 532 nm pumping, which involved different relaxation channels depending on the probe beam wavelengths. Localization of the electrons in the metastable state of NV0 centers resulted in higher saturated transmission of 632 nm pump.

Enhancement of the thermal diffusion rates of Cr and Fe in ZnSe/ZnS was studied using two different approaches. Enhancement of Cr diffusion in ZnSe was achieved by application of excess Zn atmosphere during the thermal diffusion of Cr, where ~2.2 times improvement in the diffusion coefficient was seen over the standard diffusion technique. Also, the diffusion coefficient of Fe in ZnSe and ZnS was improved by 13 and 14 times, respectively, when diffusion was done under hot isostatic pressing.

We investigate the effect of γ-irradiation on the rate of post-growth thermal diffusion of iron into ZnSe and ZnS. Samples had thin films of iron deposited on one facet and were annealed at 950°C for 14 days in the presence of γ-radiation and diffusion lengths were compared to those of traditional post-growth thermal diffusion in the absence of γ-irradiation. Samples of Fe:ZnSe and Fe:ZnS annealed under 44R/s γ-irradiation showed increases in diffusion rate of 14% and 50%, respectively.

We report a comprehensive study of γ-irradiation on optical, electrical, and laser characteristics of pure and transition-metal doped single and polycrystalline ZnS and ZnSe. Polished pure, Cr-doped, and Ag, Au, Cu, Al, In, and Mn co-doped ZnS and ZnSe crystals after absorption and electro-conductivity characterization were γ-irradiated at doses of 1.28x108 rad at −3°C. Dynamic room temperature absorption studies, electro-conductivity measurements, and mid-IR lasing were performed after different exposition times of crystals at room temperature. Cr:ZnSe and Cr:ZnS lasers based on identical γ-irradiated and non-irradiated crystals featured very similar pump thresholds, slope efficiencies, and output powers. New fluorescence band spanning over 1.3-2.1 μm in the γ-irradiated Au:Cr:ZnS was attributed to 3A2→3T2(F) transition of Cr4+.

We have demonstrated volumetric Bragg gratings (VBGs) for mid-IR spectral range based on LiF color center (LiF:CC) crystals. γ-irradiated LiF:CC crystals feature strong absorption bands in the visible and near-IR spectral range, where selective color center photo-bleaching allows for the LiF refractive index modification. The absence of active absorption in LiF:CC crystals at wavelengths longer than 1.3 μm results in a VBG that is stable under mid-IR irradiation. Our calculations predict a ~60% diffraction efficiency over 1-6 μm spectral range, which could be realized in a ~1 cm long VBG. To verify this, we fabricated periodic structures in LiF:CC crystals using an amplified femtosecond Ti:sapphire laser. Diffraction at 1.56 μm is demonstration of a phase grating in LiF and is a proof of the feasibility of LiF:CC crystals for mid-IR VBG applications.

Recent progress in fabrication and mid-IR lasing of transition metal doped II-VI single crystal and thermo-diffusion doped polycrystalline and hot-pressed ceramic gain media as well as nano and micro-crystalline laser active powders, powders in the liquid suspension, polymer-film, thin film waveguides and chalcogenides glass composites is reported.