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Optical frequency combs based on mode-locked Cr:ZnS lasers uniquely combine multi-octave bandwidth, high brightness, and compactness. We demonstrate spectroscopy with dual Cr:ZnS combs accessing 800,000 comb teeth spanning 2000 cm–1 in the middle-IR.

We report dual-comb spectroscopy with highly coherent broadband combs spanning 6– 12 µm produced via optical rectification of sub-three-cycle Cr:ZnS laser pulses. Real-time (~1sec) acquisition of broadband molecular spectra with the sub-Doppler resolution was demonstrated.

We demonstrate vector solitons in a few-cycle polycrystalline Cr:ZnS oscillator at the middle-IR wavelength 2.4 µm and deploy realistic simulations to identify χ(2) nonlinearity in a polycrystal as the main factor contributing to polarization dynamics.

We present recent results on 1645/1617 nm Er:YAG and 2090 nm Ho:YAG laser systems optically pumped by efficient CW fiber lasers. Multi-mJ pulse energy, MW-level peak powers are obtained in a range of repetition rates.

We report the first femtosecond polycrystalline Cr:ZnS oscillator with an octave-spanning spectrum. Average power of the laser is 1.4 W at the mid-IR central wavelength 2.4 μm and the pulse repetition frequency 79 MHz.

We report 45 dB single stage Cr:ZnSe amplifier operating over 2.2-2.6 μm spectral range seeded by CW Cr:ZnSe single frequency laser. The maximum output energy of 1.6 mJ was demonstrated in 25 ns pulses at 1000 Hz repetition rate.

We report dual-comb spectroscopy experiments with stabilized combs based on Kerr-lens mode-locked Cr:ZnS lasers. The compact dual-comb setup features >3W power per each channel, 80-MHz comb-mode spacing, and 60-THz-wide band centered at 2.4 μm.

We give an overview of experimental results on mid-IR femtosecond lasers and frequency combs based on polycrystalline Cr$^{2+}$: ZnS providing access to few-cycle pulses in the spectral range 2–$;3\mu \mathrm{m}$. We also discuss the techniques for generation of multi-octave coherent femtosecond continua with Cr$^{2+}$: ZnS lasers.

We report a technique for generation of ultra-broadband coherent femtosecond continua in the infrared. The laser architecture is based on the Cr:ZnS–GaSe and Cr:ZnS–ZGP tandem arrangements that enable simultaneous amplification of ultrashort middle IR pulses and augmentation of pulses’ spectrum via a chain of intrapulse three-wave mixings. The first part of the tandems is based on a single-pass polycrystalline Cr:ZnS amplifier, which is optically pumped by off-the-shelf continuous wave Er-doped fiber laser and outputs 2-cycle pulses with multi-Watt average power at 80 MHz repetition rate, at the central wavelength 2.5 μm. The second stage of the tandems comprises a GaSe or ZGP crystals configured for intrapulse difference frequency generation. The Cr:ZnS–GaSe tandem has allowed us to achieve multi-octave 2–20 μm continuum with 2 W power in the range 2–3 μm and power in excess of 20 mW in the important range 3–20 μm. On the other hand, Cr:ZnS–ZGP tandem features long-wave infrared (6–12 μm) output pulses with record braking sub-Watt power level. Last but not least, Cr:ZnS–GaSe and Cr:ZnS–ZGP IR sources have small footprints and are easily convertible to the optical frequency combs with low carrier-to-envelope timing jitter.

We report mid-IR frequency comb with 3.25 W average power and spectrum spanning 60 THz near 2.4 pm. We stabilized the offset frequency of the comb with accumulated phase error of 75 mrads.

We give an overview of recent experimental results on mid-IR femtosecond lasers and optical frequency combs based on TM:II-VI media providing access to few-cycle pulses with Watt-level power over 2–20 µm spectral range.

Enabling broad tunability, high peak and average power, ultrashort pulse duration, and all known modes of laser operation—transition-metal (TM)-doped II–VI chalcogenides are the materials of choice for direct lasing in the mid-IR. The host materials feature broad infrared transparency, high thermal conductivity, low phonon cutoff, low optical losses, and are available as either single crystals or polycrystalline ceramics. Doped with TM ions, these media exhibit a four-level energy structure, the absence of excited state absorption, as well as broad absorption and emission bands. Doped single-crystals of high optical quality are difficult to grow; however, the advent of postgrowth diffusion doped ceramics has resulted in significant progress in laser development. Here, we summarize recent experimental laser results on Cr and Fe doped II–VI chalcogenides providing access to the 1.8–6 μm spectral range with a high (>60%) efficiency, multi-Watt-level [140 W in continuous wave (CW)] output powers, tunability of >1000 nm, short-pulse (

We report, to the best of our knowledge, the first fully referenced Cr:ZnS optical frequency comb. The comb features few cycle output pulses with 3.25 W average power at 80 MHz repetition rate, spectrum spanning 60 THz in the middle-IR range 1.79–2.86 µm, and a small footprint (0.1 m2), The spectral components used for the measurement of the comb’s carrier envelope offset frequency were obtained directly inside the polycrystalline Cr:ZnS laser medium via intrinsic nonlinear interferometry. Using this scheme we stabilized the offset frequency of the comb with the residual phase noise of 75 mrads.

We demonstrate a fs laser architecture that enables the direct measurement of the laser’s carrier envelope offset frequency. A multi-Watt source is arranged as a full-repetition-rate polycrystalline Cr:ZnS MOPA and covers 3-octaves (0.4–4.2 µm).

Until recently, the generation of super-octave continua in bulk materials at full repetition rates of femtosecond (fs) oscillators has been limited to a few special cases of Kerr lens mode-locked Ti:sapphire lasers. In 2019, we described a 3.4-octave fs source with 50 nJ pulse energy at the repetition rate of 78 MHz based on polycrystalline Cr:ZnS [Vasilyev et al., Optica 6, 126 (2019)OPTIC82334-253610.1364/OPTICA.6.000126]. Here we explain the mechanism of fs supercontinuum generation in transition-metal doped polycrystalline II-VI semiconductors at relatively low (nJ-level) pulse energy. We demonstrate that this new supercontinuum regime is enabled by a complex, yet well-reproducible, interplay between the effects arising from the third-order nonlinearity, the quadratic nonlinearities, and thermal optical effects in the medium. We also demonstrate the control of fs pulse propagation in disordered χ ( 2 ) media via the control of the material microstructure.

We report, to the best of our knowledge, the first super-octave femtosecond polycrystalline Cr:ZnS laser at the central wavelength 2.4 µm. The laser is based on a non-polarizing astigmatic X-folded resonator with normal incidence mounting of the gain element. The chromatic dispersion of the resonator is controlled with a set of dispersive mirrors within one third of an optical octave over 2.05–2.6 µm range. The resonator’s optics is highly reflective in the range 1.8–2.9 µm. The components of the oscillator’s output spectrum at the wavelengths 1.6 µm and 3.2 µm are detected at –60 dB with respect to the main peak. Average power of few-cycle Kerr-lens mode-locked laser is 1.4 W at the pulse repetition frequency 79 MHz. That corresponds to 22% conversion of cw radiation of Er-doped fiber laser, which we used for optical pumping of the Cr:ZnS oscillator.

II-VI chalcogenides (e.g. ZnSe/S) doped with transition metal (TM) ions such as Cr, and Fe are arguably the materials of choice for fabrication of effective mid-IR gain media. TM:II-VI materials feature a favorable blend of laser spectroscopic parameters: a four-level energy structure, absence of excited state absorption, close to 100% quantum efficiency of fluorescence (for Cr doped II-VI media), broad mid-IR vibronic absorption and emission bands. This talk summarizes progress in fabrication of high quality Cr:ZnS/Se and Fe:ZnS/Se by cation vacancy and cation interstitial enhanced post growth thermal diffusion. We also describe recent breakthrough on recrystallization and effective doping of ZnS ceramics under hot isostatic pressing resulting in a large cm-scale monocrystalline domains formation and an increase of the Fe diffusion coefficient by three orders of magnitude. We report recent advances in high-power Cr:ZnS/Se and Fe:ZnSe laser systems, enabling a wide range of tunability (1.8-5.0µm) with output power levels of up to 140 W near 2500 nm, 32 W at 2940 nm, and 35 W at 4300 nm with corresponding optical efficiencies of 62%, 29%, and 35%. Current improvements of output characteristics of polycrystalline Cr:ZnS/Se oscillators in Kerr-Lens-Mode-Locked (KLM) regime are reported: up to 2 W output power at 75-1200 MHz repetition rate, up to 2 cycle pulse duration (16 fs) with efficiency of 20-25% with regards to Er-fiber laser pump power. The effects of efficient up-conversion of mid-IR fs pulses in the laser medium as well as supercontinuum generation are demonstrated. Further extension of mid-IR spectral coverage to 3-8 m is demonstrated by Cr:ZnS KLM laser pumped degenerate (subharmonic) parametric oscillators (OPOs) based on based on quasi-phase matching in orientation-patterned gallium arsenide, and random phase matching in polycrystalline ZnSe.

In this paper, prospects of using diamond with NV− centers as a gain medium have been studied. Spectroscopic characterization of NV− centers in diamond as well as absorption saturation and pump-probe experiments have been carried out. Absorption and emission cross-sections were estimated to be 2.8 × 10-17 cm2 and 4.3 × 10-17 cm2 at the maximum of absorption and emission bands, respectively. It was observed from emission spectra under pulse excitation that some NV− are photoionized to NV0 centers with ZPL at 575 nm. Room temperature luminescence lifetime of NV− centers was measured to be 12ns, which is close to the previously reported lifetime in bulk diamond (~13ns). Saturated transmission was only about 11% of calculated values even at energy fluence much higher than the saturation flux. Two excited state absorptions (ESAs) with different relaxation times (“fast-decay” and “slow-decay with relaxation times of ~500 ns and several tens of microseconds, respectively) were revealed in transmission decay kinetics at 632 nm. Kinetics of transmission at 670 nm was dominated by “slow-decay” ESA process. Kinetics of dk/k0 in shorter wavelength were strongly dominated by “fast-decay” ESA process. These results definitively indicate that stimulated emission of NV− centers is suppressed by photoionization and ESAs and the possibility of diamond lasers based on NV− centers is low.

We report compact ultrafast mid-IR sources based on single-pass cw and pulsed pumped polycrystalline Cr:ZnS/Se laser amplifiers exhibiting up to 37% efficiency, up to 30 dB small-signal gain, and spectral span of 1.6–4.5 um.

We demonstrate an approach to power scaling of middle-IR femtosecond pulses at the wavelength 2-3 μm to multi ten-Watt level in simple and robust single-pass spinning ring amplifier based on polycrystalline Cr:ZnSe.

Co2+:II-VI chalcogenide (e.g. ZnSe, ZnS) crystals exhibit broad emission in the 3-4µm spectral range with absorption peaks at ~0.75µm, ~1.5µm, and ~2.9µm which can be used for excitation. Laser oscillation of Fe2+ with wavelength ~4µm has been demonstrated at 14K in Co:Fe:ZnSe/ZnS under energy transfer from Co2+ ions. However, recent efforts in obtaining laser oscillation in Co2+:ZnSe/ZnS crystals have been unsuccessful. This can potentially be explained by excited state absorption at the 4T2(F)→4T1(F) transition. In addition, the laser oscillation in Co:Fe:ZnSe/ZnS co-doped crystals was only observed at temperatures under 21K. We report measurements of Co:ZnSe/ZnS absorption and emission at room temperature and 14K as well as estimates of excited state absorption from these measurements. Also, the results of experiments showed increase of absorption at 2.94µm under alexandrite laser excitation in Co:ZnS, which could result from excited state absorption. The lifetime of induced absorption was ~100µs, which is close to the ~200µs lifetime of the 4T2 level. The model of excited state absorption at low temperature predicts strong absorption over the emission spectrum of Co2+ in ZnSe, which can explain the negative lasing results. The loss of laser oscillation in co-doped crystals with increased temperature can be explained by the broadening of excited state absorption of Co2+. The spectroscopic measurements of the excited state absorption spectrum of Co:ZnSe/ZnS will be presented at the conference.

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.

We report a few-cycle, super-octave, polycrystalline Cr:ZnS laser system with 4 W power at 78 MHz repetition rate, where all of the necessary optical signals for the measurement of the carrier–envelope offset frequency are generated intrinsically.

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 Cr2+-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 Cr2+:ZnS driving source (20 fs pulse duration, 6 W average power, 78 MHz repetition rate) enabled the use of highly nonlinear ZnGeP2 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.

Progress in fabrication and mid-IR lasing of Cr and Fe thermal-diffusion and radiation enhanced thermal diffusion doped II-VI binary and ternary polycrystals is reported. We demonstrate novel design of mid-IR Fe:ZnSe and Cr:ZnSe/S solid state lasers with significant improvement of output average power up to 35W@4.1 μm and 57W@2.5 μm and 20W@2.94 μm. We report significantly improved output characteristics of polycrystalline Cr:ZnS/Se lasers in gain-switched regime: 16 mJ at 200 Hz, pulse duration 5 ns with tunability over 2400-3000 nm as well as Kerr-Lens-Mode-Locked regime in terms of average power (up to 2 W), peak power and pulse energy (0.5 MW and 24 nJ, respectively), and pulse duration (less than 29 fs).

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 be2% for both ions under 532 nm excitation wavelength.

Detailed spectroscopic characterization of Cr:ZnSe (Cr:ZnS) crystals under visible excitation into the charge transfer bands of Cr2+ impurities was performed. Middle infrared photoluminescence of Cr:ZnS under this excitation exhibits shorter rise time (~150ns) than that previously observed in Cr:ZnSe (~4-10 μs). As a result the quantum yield of Cr:ZnS mid-IR photoluminescence under 10ns pulsed 416nm excitation into the charge transfer band was estimated at close to 100%, which contrasts with low (~14%) quantum yield measured in Cr:ZnSe under 532nm pulsed excitation, indicating the possibility of efficient excitation of the upper laser level of Cr:ZnS using this mechanism. The rise time can be caused by cascade relaxation from higher lying levels through the 3T1 metastable level, producing luminescence in the near-IR. Measurements of the temperature dependence of the middle- and near infrared photoluminescence signals are reported. These values indicated that more efficient pumping of Cr:ZnSe under 532nm excitation can be achieved at temperatures greater than 300 K. Results of high temperature laser experiments supporting this idea are presented.

Spectroscopic characterization of Iron and Chromium doped ZnSe under visible excitation into the charge transfer bands of Transition Metal ions is reported. Energy transfer rates to the upper laser level are sufficient for population inversion.

Recent efforts have demonstrated efficient Cr2+ :II-VI chalcogenide (e.g. ZnSe, ZnS) broadly tunable (1.9-3.3μm) lasers under direct intra-shell Cr2+ optical excitation. We report on the spectroscopic study of Cr2++:ZnSe/ZnS under visible excitation into the charge transfer band of Cr2+ ions. Polycrystalline samples prepared by thermal diffusion method were studied. Middle-infrared (mid-IR) photo-luminescence (PL) of Cr2+ ions was compared under continuous wave (CW) direct 1532nm (5T2→5E) excitation and under 532nm excitation into charge transfer band. The quantum yield of Cr:ZnSe mid-IR luminescence under CW green excitation was estimated as close to 100% at room temperature. To estimate Cr excitation rate via charge transfer band under short pulse excitation, mid-IR PL kinetic measurements were performed with the use of 532nm picosecond and nanosecond pumping. Mid-IR PL kinetics of Cr:ZnSe under pulsed green excitation exhibit a relatively slow growth reaching a peak at ~5-10μs for nanosecond and picosecond excitations, respectively, while PL kinetics in Cr:ZnS reveal shorter measured rise time (

Cobalt doped II-VI wide band semiconductors (e.g. ZnSe, ZnS, CdSe) are promising media for infrared (IR) laser applications. They could be utilized as effective passive Q-switches for cavities of Alexandrite as well as Nd and Er lasers operating over 0.7-0.8, 1.3-1.6, and ~2.8 μm spectral ranges. We report spectroscopic characterization of Co:ZnSe and Co:ZnS crystals. Absorption cross-sections were measured for 4 A 2 (F) → 4 T 1 (P), 4 A 2 (F) → 4 T 1 (F), and 4 A 2 (F) → 4 T 2 (F) transitions with maximum absorption at 768(726), 1615(1500), 2690(2740) nm for ZnSe(ZnS) crystals, respectively. The calculated absorption cross-sections of the above transitions were estimated to be 64(56)×1019, 7.5(7.8)×1019, and 0.52(0.49)×1019 cm2 for ZnSe(ZnS) crystal hosts. In addition to the above applications the cobalt ions could be utilized for excitation of Fe 2+ ions via resonance energy transfer process. Tunable room temperature lasing of Fe 2+ doped binary and ternary chalcogenides has been successfully demonstrated over 3.5-6 μm spectral range. However, II-VI lasers based on Fe 2+ active ions don’t feature convenient commercially available pump sources (e.g. some Fe doped crystal hosts require pump wavelengths longer than 3 μm). Therefore, the process of energy transfer from Co 2+ to Fe 2+ ions could enable utilization of commercially available visible and near-infrared pump sources. We report a spectroscopic characterization of iron-cobalt co-doped ZnS and ZnSe crystals over 14-300K temperature range. Mid-IR laser oscillation at 3.9 μm(3.6 μm) via energy transfer in the Co:Fe:ZnSe (Co:Fe:ZnS) co-doped crystals was demonstrated under cobalt excitation at 4 A 2 (F) → 4 T 1 (P) (~0.7μm) and 4A2(F) → 4T1(F) (~1.56 μm) transitions.

Spectroscopic and laser characterization of Cr2+:ZnSe/ZnS under visible excitation into the charge transfer band of Cr2+ is reported. The pump rates of Cr:ZnSe/ZnS via ionization transition are sufficient for realization of population inversion and lasing.

We report on recent progress in development of new gain media for tunable (3–8 μm) mid-IR lasers as well as Fe:ZnS/Se lasers operating in CW (>1.5W), gain-switched (>1 mJ@7ns@lkHz) and long-pulse (>0.5 J@20μs) regimes.

We report on recent progress in development of new iron-doped binary and ternary mid-IR gain media for 3-8 μm spectral region and laser operation in CW, gain-switched and long-pulse regimes.

We report spectroscopic characterization of Fe:ZnSe quantum dots (for 2% of Zn/Fe molar ratio) fabricated by microemulsion hydrothermal synthesis. Mid-IR photoluminescence of the 5E↔5T2 transition of Fe2+ ions over 3.5-4.5 μm spectral range was observed in Fe:ZnSe quantum dot samples and kinetics of luminescence have been characterized at temperatures of 30-300 K under direct (2.788 μm) mid-IR excitation and indirect (0.355 μm) photoionization excitation. The radiative lifetime (τrad) was estimated from these measurements to be 48 µs while lifetime at room temperature was measured to be 440 ns. This agrees closely with the behavior of bulk material.

Mid-IR lasers based on Cr 2+ and Fe 2+ ions in II-VI tetrahedral crystal hosts have been proven useful as tunable solid-state lasers operating over the 1.9-6 μm spectral range. However, the development of new effective gain media promising for lasing over 3-4 μm and with wavelengths longer than 6 μm is still under progress. In this paper we report spectroscopic characterization of Titanium doped AgGaS 2 and Iron doped MgAl 2 O 4 crystals with coordination number four. Polarized absorption and luminescence spectra of titanium doped AgGaS 2 crystals were measured at room and low temperatures. It was shown that Ti ions in the AgGaS 2 crystal were in both 1+ and 3+ valence states substituting silver and gallium sites, correspondingly. Ti 3+ ions in AgGaS 2 and Fe 2+ in MgAl 2 O 4 crystals feature broad absorption bands with a maximums near 2μm. These ions have no second excited state absorption bands and could potentially be used as effective saturable absorbers for passive Q-switching of 2.1 μm holmium laser cavities. Broad emission covering the 3-6 μm spectral range was observed under 1.9 μm excitation into Ti 3+ absorption band. A luminescence signal between 3 and 6 μm was also observed in the Fe:MgAl 2 O 4 crystal.

Room temperature iron doped II-VI lasers have demonstrated broad band tunability between 3.5 and 6 μm with efficiency ~40%. However, these lasers require pump sources with a wavelength ~3 μm which could be selected only from a few available. Cobalt ions in the II-VI materials have strong absorption bands at 4 A 2 → 4 T 1 ( 4 P) and 4 A 2 → 4 T 1 ( 4 F) transitions located at ~0.75 and 1.5 μm, respectively. A number of different laser sources (including diode lasers) could be potentially used for cobalt excitation followed by energy transfer to iron ions. Here we report materials fabrication and study of energy transfer in Co:Fe:ZnS(ZnSe) crystals. Iron-cobalt co-doped samples were prepared using a two-stage post-growth thermal diffusion procedure with Fe concentrations of 8.5-19x10 18 cm -3 . Kinetics and photoluminescence spectra reveal energy transfer under cobalt excitation at 4 A 2 - 4 T 1 ( 4 F) transition by 1.56 μm radiation and 4 A 2 - 4 T 1 ( 4 P) transition by 0.7 μm radiation. Analysis shows effective energy transfer from 4 T 1 ( 4 F), 4 T 2 and 4 T 1 ( 4 F) Co 2+ energy levels to 5 T 2 excited level of Fe 2+ ions the first realization of Fe 2+ ions lasing at 3.6 μm and 3.8μm via Co-Fe energy transfer. Demonstrated effective Co 2+ →Fe 2+ energy transfer process could result in utilization of a more convenient laser pump sources for the Fe 2+ :II-VI lasers.

We report methods of fabrication and laser-spectroscopic characterization of mid-IR gain media based on micron size Cr2+:ZnSe/ZnS powders, as well as Cr2+:ZnSe/ZnS doped fluorocarbon polymer films, and perfluorocarbon liquids. All samples demonstrated strong mid-IR luminescence over 2000-3000nm spectral range under optical 1700nm excitation. The random lasing of the doped liquids and polymer films was realized with pump energy density of 100 and 15mJ/cm2, respectively. Previously we have demonstrated mid-IR electroluminescence of Cr:ZnSe with n-conductivity provided by thermal diffusion of Al and Zn. However, the formation of conductivity was accompanied by compensation of the Cr2+ optical centers and relatively weak chromium electroluminescence. In this paper we report study of the Cr2+ compensation in the crystals co-doped with donor and acceptor impurities. Optical and electrical characterization of Cr:ZnSe crystals with Ag, Cu, Al, In, and Zn co-dopants were studied to optimize mid-IR electroluminescens of the Cr2+ ions. The best results were obtained with p-conductive Ag:Cr:ZnSe samples featuring a low 600 Ωcm resistivity. First mid-IR electroluminescence in presumable p-type Ag:Cr:ZnSe was demonstrated, which could prove valuable for developing laser diodes that function in this spectral region.

Studies of divalent Chromium ions compensation in ZnSe crystals after thermo-diffusion of Al and Ag co-dopants are presented. We report 2-3mm Mid-IR electro-luminescence in the Al:Cr:ZnS and Ag:Cr:ZnSe bulk samples.

We report on fabrication and spectroscopic characterization of Co:(Fe:):ZnSe/S crystals for saturable absorbers and gain elements for IR solid-state lasers.