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Using sub-3-cycle pulses from mode-locked Cr:ZnS lasers at λ ≈ 2.4 µm as a driving source, we performed high-resolution dual-frequency-comb spectroscopy in the longwave infrared (LWIR) range. A duo of highly coherent broadband (6.6–11.4 µm) frequency combs were produced via intrapulse difference frequency generation in zinc germanium phosphide (ZGP) crystals. Fast (up to 0.1 s per spectrum) acquisition of 240,000 comb-mode-resolved data points, spaced by 80 MHz and referenced to a Rb clock, was demonstrated, resulting in metrology grade molecular spectra of N2O (nitrous oxide) and CH3OH (methane). The key to high-speed massive spectral data acquisition was low intensity and phase noise of the LWIR combs and high (7.5%) downconversion efficiency, resulting in a LWIR power of 300 mW for each comb.

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 present recent results on high energy, high repetition rate 1645 nm Er:YAG laser optically pumped by efficient Er-doped CW fiber lasers. Up to 32.5 mJ pulse energy, 0.85 MW-level peak powers are obtained at 1000 Hz. The results are presented in a wide 500-5000 Hz range of repetition rates.

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 develop a comprehensive model to simulate random quasi-phase-matched frequency conversion in polycrystalline media, and present simulations which shed light on the mechanisms of supercontinuum generation and the properties of generated radiation in zinc-blende materials.

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.

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.

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).

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.

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.

II-VI binary and ternary chalcogenides (e.g. ZnS, ZnSe; CdZnTe, ) doped with transition metal (TM) ions such as Cr, and Fe are arguably the materials of choice for effective mid-IR lasers potentially covering 1.8-9 µm spectral range. This talk summarizes progress in 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, as well as Fe doped ternary chalcogenides with tunability potentially extended up to 9 um. TM:II-VI media feature a unique combination of superb ultra-fast laser capabilities with high nonlinearity enabling exceptional output characteristics of polycrystalline Cr:ZnS/Se oscillators in Kerr-Lens-Mode-Locked (KLM) regime over 2-2.6 um and effective up and down conversion of fs pulses via random phase matching (RFM). Extension of mid-IR spectral coverage to 3-8 um is demonstrated by Cr:ZnS KLM laser pumped subharmonic parametric oscillators (OPOs) based on quasi-phase matching in OP-GaAs, and RFM in polycrystalline ZnSe. Fe:II-VI semiconductors are complimentary to Cr doped compounds and 3-8 um KLM ultrafast oscillators based on Fe doped chalcogenides are feasible. Another important feature of Fe:II-VI media is excellent energy storage capability at 77-200K (~60 µs luminescence life time) enabling efficient Q-switched regime and high energy amplification of ns and ultrafast pulses. One of the major problems in the development of CW, gain switched, Q-switched and KLM ultrafast Fe:II-VI lasers was the absence of convenient pump sources overlapping with absorption band (2.7-4.5 um) of Fe: gain media. Potential utilization of Quantum Cascade Lasers (QCL) as pump sources of Fe:II-VI lasers will be discussed in the form QCL-solid state laser hybrid platforms as well as Fe doped active layers integrated in QCL structures.

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.

Frequency combs with a wide instantaneous spectral span covering the 3–20 µm molecular fingerprint region are highly desirable for broadband and high-resolution frequency comb spectroscopy, trace molecular detection, and remote sensing. We demonstrate a novel approach for generating high-average-power middle-infrared (MIR) output suitable for producing frequency combs with an instantaneous spectral coverage close to 1.5 octaves. Our method is based on utilizing a highly-efficient and compact Kerr-lens mode-locked Cr2+:ZnS laser operating at 2.35-µm central wavelength with 6-W average power, 77-fs pulse duration, and high 0.9-GHz repetition rate; to pump a degenerate (subharmonic) optical parametric oscillator (OPO) based on a quasi-phase-matched GaAs crystal. Such subharmonic OPO is a nearly ideal frequency converter capable of extending the benefits of frequency combs based on well-established mode-locked pump lasers to the MIR region through rigorous, phase- and frequency-locked down conversion. We report a 0.5-W output in the form of an ultra-broadband spectrum spanning 3–8 µm measured at 50-dB level.

We demonstrate an optical parametric oscillator (OPO) based on random phase matching in a polycrystalline χ(2) material, ZnSe. The subharmonic OPO utilized a 1.5-mm-long polished ZnSe ceramic sample placed at the Brewster's angle and was synchronously pumped by a Kerr-lens mode-locked Cr:ZnS laser with a central wavelength of 2.35 μm, a pulse duration of 62 fs, and a repetition frequency of 79 MHz. The OPO had a 90-mW pump threshold, and produced an ultrabroadband spectrum spanning 3-7.5 μm. The observed pump depletion was as high as 79%. The key to success in achieving the OPO action was choosing the average grain size of the ZnSe ceramic to be close to the coherence length (~ 100 μm) for our 3-wave interaction. This is the first OPO that uses random polycrystalline material with quadratic nonlinearity and the first OPO based on ZnSe. Very likely, random phase matching in ZnSe and similar random polycrystalline materials (ZnS, CdS, CdSe, GaP) represents a viable route for generating few-cycle pulses and multi-octave frequency combs, thanks to a very broadband nonlinear response.

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 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.

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.

High-power (0.5 W) mid-IR output suitable for ultra-broadband frequency comb generation was produced in a subharmonic GaAs optical parametric oscillator that was synchronously pumped by a compact 0.9 GHz, 6 W femtosecond Cr:ZnS (2.35μm) MOPA.

Transition metal (TM) doped II-VI chalcogenide laser materials offer a unique blend of physical, spectroscopic, and technological parameters that make them the gain media of choice for cost effective broadly tunable lasing in the Mid-IR. The II-VI semiconductor hosts provide a low phonon cut-off, broad IR transparency, and high thermal conductivity. When doped with transition metal ions, these materials feature ultrabroadband gain, low saturation intensities, and large pump absorption coefficients. This combined with the low-cost mass production technology of crystal fabrication by postgrowth thermal diffusion, as well as broad availability of convenient pump sources, make these materials ideal candidates for broadly tunable mid-IR lasing in CW, gain-switched, free running, and mode-locked regimes of operation. This review summarizes experimental results on optically pumped lasers based on Cr and Fe doped II-VI wide band semiconductors providing access to the 1.9-6 μm spectral range with a high (exceeding 60%) efficiency, multi-Watt-level (18 W in gain switch and 30 W in pure CW) output powers, tunability in excess of 1000 nm, short-pulse (

This paper summarizes recent improvements of output characteristics of polycrystalline Cr:ZnS/Se master oscillators in Kerr-Lens-Mode-Locked regime. We developed a flexible design of femtosecond polycrystalline Cr:ZnS and Cr:ZnSe lasers and amplifiers in the spectral range 2–3 μm. We obtained few-optical-cycle pulses with multi-Watt average power in very broad range of repetition rates 0.08–1.2 GHz. We also report on efficient nonlinear frequency conversion directly in the polycrystalline gain elements of ultra-fast lasers and amplifiers. In this work we also report on recent progress in spinning ring gain element technology and report to the best of our knowledge the highest output power of 9.2 W Fe:ZnSe laser operating in CW regime at 4150nm.

We demonstrate an approach to a middle-IR frequency comb generator, which uniquely combines Watt-level power, exceptionally broad spectrum and small footprint. The source is based on an OP-GaAs OPO synchronously pumped by a Cr:ZnS femtosecond MOPA.

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.

We report the measurement of high-order harmonics from a ZnO crystal with photon energies up to 11 eV generated by a high-repetition-rate femtosecond Cr:ZnS laser operating in the mid-infrared at 2–3 μm, delivering few-cycle pulses with multi-watt average power and multi-megawatt peak power. High-focus intensity is achieved in a single pass through the crystal without a buildup cavity or nanostructued pattern for field enhancement. We measure in excess of 108 high-harmonic photons/second.

Availability of compact and cost-efficient mid-infrared (MIR) laser sources with a broad range of parameters is of great interest for a number of current and emerging applications. For instance, femtosecond (fs) MIR sources with high average power and broad spectral span enable high dynamic range spectroscopy, sensing, and imaging in the molecular fingerprint region. On the other hand, few-optical-cycle MIR pulses with high energy are of particular importance for the development of EUV and X-ray sources based on strong field nonlinear optics, e.g. high harmonic generation. Furthermore, high-power mid-IR lasers are of interest for processing polymers, glasses and composites, surgical, dental and cosmetology procedures, as well as numerous defense-related applications.

This paper summarizes recent improvements of output characteristics of polycrystalline Cr:ZnS/Se master oscillators in Kerr-Lens-Mode-Locked regime: 1.9 W average power at 41 fs pulse duration, 24 nJ pulse energy and 515 kW peak power with efficiency of 19% with regards to 1567 nm pump power from linearly polarized Er-fiber laser. A simple design of mid-IR fs Cr:ZnS MOPA enabled power scaling to 6.8 W at 79 MHz repetition rate. This was accompanied by a 2 fold spectral broadening to 600 nm at -10 dB level, pulse compression from 44 to

Cr2+ doped ZnS and ZnSe possess a unique blend of physical, spectroscopic, and technological parameters. These laser materials feature ultra-broadband gain in 1.9 – 3.3 μm mid-IR range, low saturation intensities, and large pump absorption coefficients. The II-VI semiconductor hosts provide a low phonon cut-off, broad IR transparency, and high second and third order nonlinearity. Cr:ZnS and Cr:ZnSe are available in polycrystalline form: the material consists of a multitude of microscopic single-crystal grains with a broad distribution of grain sizes and orientations, which results in random quasi-phase-matching (RQPM). The distinctive features of RQPM are a linear dependence of the conversion yield with length of the medium and ultra-wide bandwidth of three-wave mixing. We review resent experimental results on optically pumped mid-IR ultrafast lasers based on polycrystalline Cr:ZnS and Cr:ZnSe. We demonstrate that Kerrlens mode-locking of polycrystalline Cr:ZnS and Cr:ZnSe lasers allow for generation of few-cycle mid-IR pulses with MW-level peak power. This opens several avenues for efficient nonlinear frequency conversion of short optical pulses directly in the laser gain medium via RQPM process. We implemented Kerr-lens mode-locked Cr:ZnS oscillators, which feature high power (up to 0.25 W), spectrally broad (up to 22 THz) second harmonic generation (SHG) in the laser medium. We also demonstrate simple and robust ultrafast source based on single-pass continuously pumped polycrystalline Cr:ZnS laser amplifier: mid-IR pulses with 6.8 W average power and the spectrum spanning 2.0–2.6 μm as well as SHG pulses with 0.52 W average power and 1.05 – 1.25 μm spectral span were obtained.

We report compact ultrafast mid-IR source based on single-pass continuously pumped polycrystalline Cr:ZnS laser amplifier: 30 fs pulses with the spectrum spanning 2.0-2.6 µm (-10 dB) at 7.3 W overall power were obtained.

We report flexible design of femtosecond middle-IR lasers with a broad range of repetition rates 0.08–1.2 GHz. The lasers emit few-cycle pulses with 4–16.4 THz bandwidth, 0.1– 21 nJ energy at 2.4 µm wavelength.

We report Kerr-lens mode-locked polycrystalline Cr(2+):ZnS lasers at 2.4 μm central wavelength optimized for short pulse duration. By control of the second- and third-order dispersion within 500 nm bandwidth we obtained pulses of three optical cycles (29 fs) at 100 MHz repetition rate with 0.44 W average power. The emission spectrum is 240 nm broad at -3 dB level and spans 950 nm at -30 dB level. Transform-limited 38 fs pulses were obtained at 300 MHz repetition rate with 700 mW average power. To the best of our knowledge these are the shortest reported to-date pulses from Cr(2+):ZnS and Cr(2+):ZnSe lasers.

We report femtosecond polycrystalline Cr2+:ZnS laser at 2.4 μm central wavelength with 41 fs pulse duration, 1.9 W average power and 79 MHz pulse repetition rate that corresponds to 0.5 MW peak optical power.

We report on novel design of tunable mid-IR Fe:ZnSe and Cr:ZnSe solid state lasers which provided significant increase of output average power up to 35W@4.1 µm and 57W@2.5 µm and 20W@2.94 µm.

This Publisher’s Note corrects a misprinted unit of measure and clarifies a phrase in Optica4, 617 (2017)OPTIC82334-253610.1364/OPTICA.4.000617.

Transition-metal-doped II-VI semiconductors possess a unique blend of physical, spectroscopic, optical, and technological parameters. These materials enable high power lasers in important middle-infrared range. Furthermore, they combine superb ultra-fast laser capabilities with high nonlinearity and polycrystalline microstructure, which provides random quasi-phase matching. We developed flexible design of femtosecond polycrystalline Cr:ZnS and Cr:ZnSe lasers and amplifiers in the spectral range 2–3 µm. We obtained few-optical-cycle pulses with a multi-Watt average power in a very broad range of repetition rates 0.07–1.2 GHz. We also report on efficient nonlinear frequency conversion directly in the polycrystalline gain elements of ultra-fast lasers and amplifiers including second harmonic generation with sub-Watt power and generation of an octave-spanning middle-infrared supercontinuum.

We demonstrate an optical parametric oscillator (OPO) based on random phase matching in polycrystalline ZnSe. The OPO was pumped by Cr:ZnS laser pulses (2.35 μm, 62 fs, 79 MHz), had a pump threshold of 90 mW, and produced an ultrabroadband spectrum spanning 3–7.5 μm.

We demonstrate Kerr-lens mode-locked polycrystalline Cr2+:ZnSe and Cr2+:ZnS lasers with pulse duration of 125 fs, 160 MHz pulse repetition rate and output power of 60 mW (Cr2+:ZnSe) and 30 mW (Cr2+:ZnS).

Progress in fabrication and mid-IR lasing of Cr and Fe thermal-diffusion doped ZnSe/S polycrystals is reported. Multi-Watt-level (30W) CW output, tunability in excess of 1000nm, short-pulse (

We report femtosecond polycrystalline Cr2+:ZnS/ZnSe lasers at 80 MHz rep-rate, with pulse duration up to 44 fs, output power reaching 1.7 W and 0.25 W at 2.3 µm fundamental and second harmonic (SHG) wavelengths respectively.

We report a significant breakthrough in the development of fiber-pumped high-power CW laser systems based on Cr2+:ZnS and Cr2+:ZnSe gain media. We demonstrate output power levels of up to 140 W near 2500 nm, and 32 W at 2940 nm with corresponding optical efficiencies of 62% and 29%. Our novel approach is based on rapid simultaneous scanning of the collinear laser mode and pump beam across the Cr:ZnS/Se gain element which allows us to virtually eliminate thermal lensing effects and obtain unprecedented levels of output power with very high optical-to-optical efficiency.