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We report mechanically Q-switched 2.94 µm Er:YAG laser based on spinning mirror with 805 mJ output energy in a single 61 ns pulse at 1 Hz repetition rate and 670 Hz rotational rate of the spinning mirror. This record output energy was achieved with the use of 300 mm long MQS Er:YAG laser cavity consisted of 70% output coupler, 7x120 mm AR coated Er(50%):YAG crystal and spinning HR mirror. The maximum output energy was limited by the optical damage of the Er:YAG AR coatings.

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 was obtained to be 2.5 mJ at 32 mJ of pump energy. The measured slope efficiency was 8% with respect to the pump energy. In this experiment, 3.2 mm hot-pressed Fe:ZnSe ceramic sample was used which had 6% active transmission at the pump wavelength. By using absorption cross-section, the concentration of Fe2+ ions was calculated to be N=9*10^18 cm-3.

We study the decay kinetics of excited state of GR1 center in diamond using 633 nm pump pulse and 658 nm CW probe beam. The absorption saturation followed by a strong absorption of the probe below steady-state transmission level was observed. The recovery of the centers to the original level occurs slowly with ~500 ns time scale and reveals multi-exponential rates with no long-term bleaching or residual absorption. The branching ratio for relaxation process to the ground state and to the metastable state was estimated to be ~ 0.50.

We report on mid-IR Fe:ZnSe master oscillator power amplifier (MOPA) laser system operating at room temperature (RT) pumped by a radiation of mechanically Q-switched Er:YAG laser operating at 2.94 m, at 3Hz repetition rate. The maximum output energy was as high as 250mJ in ~250 ns pulses. The RT gain-switched Fe:ZnSe master oscillator demonstrated tunability over 3.60-5.15 µm spectral range with a maximum output energy of ~3 mJ. The output energies of 12 (8), 34 (25) and 60 (48) mJ were demonstrated at 4.4 (4.1) µm in the 1st, 2nd and 3rd stages of amplifier, respectively, with a total pump energy of 200 mJ.

External cavity diamond Raman laser pumped by 8.3 ns (10 Hz) single frequency 532 nm pump was studied. The output energy of 4.2 mJ and 2 mJ at first (573 nm) and second (620 nm) Stokes, respectively, was demonstrated for 12 mJ of pump energy with the total conversion efficiency of 51%. The minimum first Stokes pulse duration of 420 ps in backward and 500 ps in forward directions were measured under 3.5 mJ of pump energy and 7.5 mJ (9 mJ) of output energy in backward (forward) Raman signal.

We report a subharmonic (frequency-divide-by-2) optical parametric oscillator (OPO) with a continuous wavelength span of 3 to 12 µm ( − 37 d B level) that covers most of the molecular rovibrational “signature” region. The key to obtaining such a wide spectral span is the use of an OPO with a minimal dispersion—through the choice of intracavity elements, the use of all gold-coated mirrors, and a special “injector” mirror. The system delivers up to 245 mW of the average power with the conversion efficiency exceeding 20% from a 2.35 µm Kerr-lens mode-locked pump laser.

We report a flashlamp pumped mechanically Q-switched (MQS) 2.94 μm Er:YAG laser based on a spinning mirror with a highest output energy of 805 mJ at a pulse duration of 61 ns and 13 MW of peak power at 1 Hz repetition rate. This record output energy was achieved with the use of 300 mm long MQS Er:YAG laser cavity consisting of a 70% output coupler, 7 × 120 mm AR coated Er(50%):YAG crystal, and 4200 rad/s angular speed of the spinning mirror. The pulse jitter was also measured by using optical triggering and was smaller than 10 ns for 150 ns Q-switched pulses, which could be applicable to many laser applications where precise synchronization of pulses is required.

We report the first room-temperature gain-switched Fe:ZnSe hot-pressed ceramics laser pumped by 2.94 μm radiation of mechanically Q-switched Er:YAG laser. The maximum output energy was 41 mJ with 25% slope efficiency at 3Hz repetition rate.

10 {\mu}m lasing is studied in a compact CO2-He cell pressurized up to 15 atm when optically pumped by a ~50 mJ Fe:ZnSe laser tunable around 4.3 {\mu}m. The optimal pump wavelength and partial pressure of CO2 for generating 10 {\mu}m pulses are found to be ~4.4 {\mu}m and 0.75 atm, respectively. Without cavity optimization, the optical-to-optical conversion efficiency reached ~10% at a total pressure of 7 atm. The gain lifetime is measured to be ~1 {\mu}s at pressures above 10 atm, indicating the feasibility of using high-pressure optically pumped CO2 for the efficient amplification of picosecond 10 {\mu}m pulses., Comment: 10 pages, 8 figures

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.

The 658 nm probe kinetics revealed strong bleaching and multiexponential decay of the excited level with additional relaxation via intersystem crossing. The origin of induced excited state absorption was due to some other center impurity center.

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.

The neutral vacancy (GR1) centers are the intrinsic lattice defects in diamond with interesting optical properties. In the present work, we performed optical characterization of the GR1 centers in CVD-grown bulk diamond to explore their laser feasibility. The non-linear optical measurements reveal efficient saturable absorption of ground level of the centers under ns-pulsed excitation at 632 nm. The transmission changes from 55% at small incident intensity to 84% at the saturated level. The experimentally measured data was fitted with equations representing two limiting cases and obtained the saturation parameters, namely saturation fluence (6.8 mJ/cm2) and saturation intensity (6.4 MW/cm2), at 633 nm for ground state absorption. The intensity of saturation 6.4 MW/cm2 obtained after fitting the experimental data is two orders of magnitude smaller than that at 694 nm documented in the literature for GR1 centers in natural diamond. The calculation gives essentially the same value of absorption cross-section (⁓4.5 × 10-17 cm2) at 633 nm for both approximations. We also estimated the radiative lifetime and quantum yield as about 8.5 ns and 13%, correspondingly. The cross-sections were estimated for transition 1E ↔ 1T2. The emission cross-section was obtained to be ⁓9 × 10-17 cm2 near the maximum of emission band. Such a high absorption cross-section and fast recovery of ground state in combination with high concentration of the centers can provide high optical gain.

There is strong demand for effective gain materials for the 3.0-3.9 μm spectral range not nicely covered by Cr:ZnSe and Fe:ZnSe amplification bands. We characterized, Fe:ZnAl2O4 ceramic sample, Fe:MgAl2O4 and Fe:InP single crystals as promising laser materials for this mid-IR spectral range. In all crystals, the absorption bands corresponding to 5E↔5T2 transition of Fe2+ ions in the tetrahedral sites were measured. In addition, absorption band of Fe2+ ions in the octahedral sites were observed in Fe:ZnAl2O4 sample with maximum absorption cross-section at ~1.0 μm. From the absorption measurements, the radiative lifetime of Fe:MgAl2O4 was calculated to be 60 μs. Saturation absorption of Fe2+ ions in Fe:ZnAl2O4 was studied using Ho:YAG@2.09 μm and Er:YAG@2.94 μm lasers. Saturation measurements were taken up to energy density of 2 J/cm2 and showed no saturation of absorption. This can be explained by a fast non-radiative (

We report laser operation of spinning mirror mechanically Q-switched (MQS), flashlamp pumped 2.94 μm Er:YAG laser depending on the angular speed of the mirror, repetition rate, size and temperature of the gain element, pulse duration and jitter of Q-switch pulses, as well as pump pulse energy. The highest output energy of 260 mJ with a pulse duration of 150 ns was realized with the use of 7×120 mm Er(50%):YAG at 5 Hz repetition rate and 4200 rad/s angular speed of the spinning mirror. The efficiency of Q-switched operation was ~50% with respect to free-running regime. Using optical triggering, the pulse jitter was measured to be smaller than 10 ns for 160 ns Q-switched pulses. Optical triggering could be used for synchronization with mode-locked laser in chirp-pulse and regenerative amplifiers. We also report on development of room temperature gain-switched Fe:ZnSe laser pumped by a radiation of MQS Er:YAG laser. The maximum output energy of 9 mJ from Fe:ZnSe laser was demonstrated using MQS Er:YAG laser as pump source.

We report the first room temperature gain switched hot-pressed Fe:ZnSe ceramic laser pumped by radiation of 2.94 μm mechanically Q-switched Er:YAG laser. The maximum output energy was 1.5 mJ (90 ns) with 15% slope efficiency.

We report on saturation of GR1 centers absorption resulting in ~70% inversion. Probe kinetics revealed strong bleaching of ground level followed by relaxation to metastable level with branching ratio ~0.5.

We report the mechanically Q-switched 2.94 µm Er: YAG laser with a record 350 mJ output energy at 3 Hz repetition rate with 160 ns pulse duration and ~10 ns pulse jitter for fine synchronization of pulses.

We report on room temperature Fe:ZnSe MOPA system tunable over 3.6-5.2 µm pumped by radiation of Q-switched 2.94 µm Er:YAG laser. The maximum output energy was measured to be 60mJ under 200mJ of pump energy.

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 report optical characterization of Fe:ZnSe hot-pressed ceramics and demonstrate first room-temperature gain-switched lasing of this new ceramic medium. The maximum output energy was measured to be 0.7 mJ at 3.5% slope efficiency.

We used a dispersionless-cavity subharmonic OPO pumped by femtosecond 2.35-pm pulses to demonstrate a coherent output spanning 3-12pm with up to 245-mW power. We also compare the performance of the OP-GaP vs OP-GaAs crystal.

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.

Chromium doped II-VI semiconductors (such as ZnSe and ZnS) feature broad mid-IR emission in the 2-3 μm spectral range due to intershell transitions of the Cr2+ ions. These materials show much promise for development of a tunable, electrically-pumped, mid-IR laser source. For integration into a mid-IR active multilayered structure, the ternary alloy ZnSxSe1-x is an attractive waveguiding material due to its lattice-matching ability and lower index of refraction with respect to the Cr2+:ZnSe active material. Epitaxial growth of each layer is desired to achieve the electronic and optical properties necessary for successful integration into a lasing device, so a study was conducted on the effects of sulfur content and growth temperature on the crystal quality of the resulting thin films. Several films of ZnSxSe1-x were deposited by pulsed laser deposition (PLD) using a 248 nm KrF excimer laser source at varying growth temperatures and with various compositional parameters onto (100) GaAs substrates. The samples were analyzed via x-ray diffraction (XRD) and energy dispersive x-rays (EDX) to investigate the crystal quality and elemental content of the films for device integration. Film-substrate epitaxy was achieved and upper bounds to the defect density were calculated for several regimes of compositional parameter and growth temperature. From all samples produced, the lowest defect density of 2.2 x 1010 cm-2 was observed for the x=0.06 film grown at 450°C, while the lowest lattice mismatch between the substrate and epilayer of 0.059% was observed for the x=0.02 film grown at 450°C.

The present study, for the first time, reports the successful consolidation of chromium doped zinc sulfide (ZnS) polycrystalline infrared (IR) transparent ceramics (maximum transmittance of 67% at 11.6 μm) via hot pressing under vacuum. The phase composition of the as-sintered Cr2+:ZnS ceramics was determined to be primarily cubic ZnS sphalerite, with a minor amount of hexagonal ZnS wurtzite. Scanning electron microscopy (SEM) observation of the sintered ceramics showed a highly consolidated microstructure. IR absorption and photoluminescence measurements revealed that the Cr2+ ions are tetrahedrally coordinated within the ZnS host lattice.

Idiopathic pulmonary fibrosis (IPF) is a progressive disease, with a median survival of 3-5 years following diagnosis. Lung remodeling by invasive fibroblasts is a hallmark of IPF. In this study, we demonstrate that inhibition of vimentin intermediate filaments (VimIFs) decreases the invasiveness of IPF fibroblasts and confers protection against fibrosis in a murine model of experimental lung injury. Increased expression and organization of VimIFs contribute to the invasive property of IPF fibroblasts in connection with deficient cellular autophagy. Blocking VimIF assembly by pharmacologic and genetic means also increases autophagic clearance of collagen type I. Furthermore, inhibition of expression of collagen type I by siRNA decreased invasiveness of fibroblasts. In a bleomycin injury model, enhancing autophagy in fibroblasts by an inhibitor of VimIF assembly, withaferin A (WFA), protected from fibrotic lung injury. Additionally, in 3D lung organoids, or pulmospheres, from patients with IPF, WFA reduced the invasiveness of lung fibroblasts in the majority of subjects tested. These studies provide insights into the functional role of vimentin, which regulates autophagy and restricts the invasiveness of lung fibroblasts.

Iron-doped binary and ternary chalcogenide crystals are very promising for tunable solid-state lasers operating over the 3-6 μm spectral range. The most significant results have been reported for iron doped ZnSe crystals with 9.6 W output power in CW at 77K when pumped by radiation of Cr:ZnSe laser, and 1.4 J at ~150 ns pulse duration at room temperature (RT) when pumped by the radiation of HF laser. The lifetime of the upper laser level 5T2 of the Fe2+ ion in a ZnSe matrix falls with temperature from 52µs at 77 K to 370 ns at RT due to the increase of nonradiative relaxation. It allows effective laser oscillation in the gain-switched regime at RT and operation in Q-switched regime at low temperature. We report on RT gain-switched Fe:ZnSe lasers tunable over 3.60-5.15 µm pumped by radiation of mechanically Q-switched Er:YAG laser operating at 2.94 µm. The maximum output energy was measured to be 5 mJ under 15mJ of pump energy. The long upper level lifetime of Fe:ZnSe gain medium is sufficient for energy storage with pumping by radiation of free running Er:YAG lasers. We demonstrated that Q-switched regime of oscillation could be effectively utilized for Fe:ZnSe lasers. The rotating back mirror was used as a mechanical Q-switcher of a Fe:ZnSe laser. The maximum output energy in single 150 ns pulse was measured to be 3mJ which is ~25% from the theoretical limit. This approach could be attractive for development of high-energy short-pulse solid-state mid-IR systems operating over 3.6-5.0 µm spectral range

Recent progress in iron doped II-VI chalcogenide laser materials enabled important advancements in room temperature high energy, high power laser systems operating over 3.5-6.0 um. However, a lack of efficient and convenient pump sources for direct pumping of Fe(2+) ions limits possible applications of these materials. One viable option is using readily available pump sources to excite iron centers via Forster-Dexter energy transfer between transition metal ions. This paper reports on the characterization of iron-chromium and iron-cobalt energy transfer in Fe:Cr:ZnSe and Fe:Co:ZnSe co-doped crystals. The kinetics photoluminescence and spectroscopic measurements at 5T2-5E chromium and iron transitions indicated an efficient resonance energy transfer between ions even at room temperature. It was demonstrated that an energy transfer rate in Fe-Cr centers could be shorter than the upper level lifetime of Fe(2+) ions in ZnSe with total TM ions concentration larger than 10^19 cm^-3. Therefore, this mechanism can serve as an effective pump pathway for Fe lasing. Analysis of the dipole-dipole coupling between Fe(2+) and Cr(2+) ions demonstrated the for the shortest distance between iron and chromium ions in ZnSe host, the energy transfer rate is smaller than 1 ns. The absence of excited state absorption in Fe:Cr:ZnSe host make this materials more attractive in comparison with Fe:Co:ZnSe where Fe lasing due to excited state absorption of Co(2+) ions was limited only to low (

Kerr-lens mode locked lasers based on polycrystalline Cr:ZnS and Cr:ZnSe have come of age and, arguably, represent the most viable route for generation of ultra-short pulses in the range 2–3 μm. Developed designs of Kerr-lens mode locked oscillators feature high efficiency and provide access to few-cycle MIR pulses with Watt-level power in a very broad range of pulse repetition rates. However, currently available dispersive mirror coatings limit spectral coverage of these oscillators to below one octave hampering their conversion to frequency combs via frequency envelop offset frequency (fceo) control and stabilization. Supercontinuum (SC) generation using photonic waveguides is a promising approach for spectral broadening of pulsed coherent sources at low pulse energies and small footprint. Among many materials promising for this application stoichiomentric Si3N4 (SiN) holds a unique place due to its high nonlinearity, CMOS compatible fabrication process, and spectral coverage over visible-middle-infrared (MIR) range. In the current paper we experimentally demonstrate the generation of a supercontinuum spanning more than 1.5 octaves over 1.2-3.7 um range in a silicon nitride waveguide using sub-40-fs pulses at 2.35 um generated by 75 MHz Cr:ZnS laser. The coupling efficiency was about 16%, which corresponds to 0.56nJ pulse energy and 12.4 kW peak power. We also have observed that threshold for SC generation was about 50 mW of incident power that corresponds to 2.4KW peak power. The demonstrated coherent 1.5 octaves spanning bandwidth is ideal for self-referenced f-2f detection of the fceo. In addition, this represents a promising broadband coherent source for dual comb spectroscopy.

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).

This joint issue of Optics Express and Optical Materials Express features 28 state-of-the-art articles written by authors who participated in the international "Advanced Solid State Lasers" conference, held in Boston November 4-8, 2018. This review provides a summary of these articles that cover the spectrum of solid state lasers from materials research to sources and from design innovation to applications.

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.

This Joint Issue of Optics Express and Optical Materials Express features 15 articles written by authors who participated in the international online conference Advanced Solid State Lasers held 13–16 October, 2020. This review provides a summary of the conference and these articles from the conference which sample the spectrum of solid state laser theory and experiment, from materials research to sources and from design innovation to applications.

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, 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.

We report on a RT gain-switched Fe:ZnSe master oscillator power amplifier (MOPA) system tunable over 3.8–5.0 µm pumped by radiation of Er:YAG laser operating at 2.94 µm. The mechanically Q-switched Er:YAG laser with output energy up to 220 mJ was used as a pump source for a master oscillator and three-stage power amplifier. The maximum output energies in 200 ns pulses exceeded 60, 56, and 48 mJ at 4.4, 4.3, and 4.1 µm, respectively, under 220 mJ of pump energy. The extraction energy efficiencies were measured to be 25, 30, and 40% at the first, second, and third stages, respectively.

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.

We report on the highly efficient, octave-spanning mid-infrared (mid-IR) optical parametric amplification (OPA) in a ZnGeP2 (ZGP) crystal, pumped by a 1 kHz, 2.4 μm, 250 fs Cr:ZnSe chirped-pulse amplifier. The full spectral coverage of 3−10 μm with the amplified signal and idler beams is demonstrated. The signal beam in the range of ∼3 − 5 μm is produced by either white light generation (WLG) in YAG or optical parametric generation (OPG) in ZGP using the common 2.4 μm pump laser. We demonstrate the pump to signal and idler combined conversion efficiency of 23% and the pulse energy of up to 130 μJ with ∼2 μJ OPG seeding, while we obtain the efficiency of 10% and the pulse energy of 55 μJ with ∼0.2 μJ WLG seeding. The OPA output energy is limited by the available pump pulse energy (0.55 mJ at ZGP crystal) and therefore further energy scaling is feasible with multi-stage OPA and higher pump pulse energy. The autocorrelation measurements based on random quasi-phase matching show that the signal pulse durations are ∼318 fs and ∼330 fs with WLG and OPG seeding, respectively. In addition, we show the spectrally filtered 30 μJ OPA output at 4.15 μm suitable for seeding a Fe:ZnSe amplifier. Our ultrabroadband femtosecond mid-IR source is attractive for various applications, such as strong-field interactions, dielectric laser electron acceleration, molecular spectroscopy, and medical surgery.

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 first OPO based on random phase matching. The OPO was based on ZnSe ceramic pumped by 62-fs, λ=2.35-μm Cr:ZnS laser pulses, had 90-mW pump threshold and produced an ultra-broad spectrum spanning 3−7.5 μm.