Pumping Scheme Research Articles

Efficient few-cycle Yb-doped laser oscillator with Watt-level average power.

So far, the operation of ultrafast bulk laser oscillators based on Yb-doped gain materials and directly emitting few-cycle pulses have been restricted to low optical-to-optical efficiencies and average output powers of only a few milliwatt. This performance limitation can be attributed to the commonly-applied standard collinear pumping scheme in which the optical pump is transmitted through a dichroic mirror whose spectral transmission and dispersion properties severely perturb the oscillating pulse when its optical spectrum extends towards the pump wavelength. In this study, we report on a novel pumping scheme relying on cross polarization that overcomes this challenge. In our concept, the pump transmitting mirror is highly transmissive for the pump light in p-polarization, while it is highly reflective for the laser light in s-polarization over a broad wavelength range, even covering the pump wavelength and beyond. In contrast to a standard thin-film polarizer featuring similar polarization dependent properties, it provides a low and flat dispersion profile over a broad spectral range for the s-polarization. Implementing this pumping scheme in a soft-aperture Kerr-lens mode-locked bulk laser oscillator based on the gain material Yb:CALGO, we achieve clean 22-fs soliton pulses at 729 mW of average output power and an optical-to-optical efficiency of 25%. In a second configuration optimized for the highest average output power, we demonstrate a high optical-to-optical efficiency of 36.6%, which was obtained for 31-fs pulses at 1.63 W of average output power. In a third configuration we experimentally confirm the limiting effect of a dichroic mirror commonly used in the standard collinear pumping scheme. All the results presented here and obtained in the first and second configuration generate pulses with a center wavelength ranging from 1030 nm to 1056 nm, well within the spectral region of high gain cross sections of Yb:CALGO. While this initial demonstration was realized using a commercial diffraction-limited fiber laser as pump source, the pump geometry appears also well suited for pumping with laser diodes coupled into multimode fibers. This novel approach opens up new opportunities for compact and cost-efficient high-power few-cycle bulk laser oscillators based on Yb-doped gain materials and can be applied to any gain material with small quantum defect.

Near-optimal intense and powerful terahertz source by optical rectification in lithium niobate crystal

Using a 400 μJ ytterbium laser combined with a novel pulse compression technique, we demonstrate a state-of-the-art terahertz (THz) source from the tilted-pulse front pumping scheme in lithium niobate at room temperature with record efficiency of 1.3% capable of generating 74 mW of average power and 400 kV/cm at focus. Key points of this demonstration include the use of a pump pulse duration of 280 fs in combination with a stair-step echelon mirror and an off-axis ellipsoidal mirror. This source has unmatched characteristics of generating intense and powerful THz pulses at the same time and remains highly scalable as compared to existing Ti:sapphire-based THz sources pumped in the millijoule range.

On the optimality of optical pumping for a closed Λ-system with large decay rates of the intermediate excited state

We use optimal control theory to show that for a closed Λ-system where the excited intermediate level decays to the lower levels with a common large rate, the optimal scheme for population transfer between the lower levels is actually optical pumping. In order to obtain this result we exploit the large decay rate to eliminate adiabatically the weakly coupled excited state, then perform a transformation to the basis comprised of the dark and bright states, and finally apply optimal control to this transformed system. Subsequently, we confirm the optimality of the optical pumping scheme for the original closed Λ-system using numerical optimal control. We also demonstrate numerically that optical pumping remains optimal when the decay rate to the target state is larger than that to the initial state or the two rates are not very different from each other. The present work is expected to find application in various tasks of quantum information processing, where such systems are encountered.

Influence of Pump Properties on the Tunability of 1.5 μm Low-Noise Single Frequency Fiber Amplifier

In this work, we investigate the impact of the pump configuration (wavelength and pump scheme i.e., backward forward) on the tuning range in a watt level low intensity noise single-frequency Erbium/Ytterbium doped fiber amplifier. Two different pump wavelengths, 976 nm and 940 nm, and three different pumping schemes were numerically and experimentally investigated. Tunability over 47 nm (1533 nm-1580 nm) with relative intensity noise level as low as −155 dB/Hz is achieved using an unconventional pumping scheme where the active fiber is pumped in both directions with two different pump wavelengths.

Six kilowatt record all-fiberized and narrow-linewidth fiber amplifier with near-diffraction-limited beam quality

Abstract In this work, an all-fiberized and narrow-linewidth fiber amplifier with record output power and near-diffraction-limited beam quality is presented. Up to 6.12 kW fiber laser with the conversion efficiency of approximately 78.8% is achieved through the fiber amplifier based on a conventional step-index active fiber. At the maximum output power, the 3 dB spectral linewidth is approximately 0.86 nm and the beam quality factor is M x 2 = 1.43, M y 2 = 1.36. We have also measured and compared the output properties of the fiber amplifier employing different pumping schemes. Notably, the practical power limit of the fiber amplifier could be estimated through the maximum output powers of the fiber amplifier employing unidirectional pumping schemes. Overall, this work could provide a good reference for the optimal design and potential exploration of high-power narrow-linewidth fiber laser systems.

Management of an Aquifer Threatened by Saltwater Intrusion: Borrowing from Pollution Control Strategies

In a region that is surrounded by multiple bodies of water, inundated by seasonal rains, and threatened by floods, water is not a resource that South Louisianians often think much about over consuming. However, over-pumping threatens one of the state’s largest groundwater reserves and sources of high-quality drinking water: the Southern Hills Aquifer System, which provides valuable freshwater supply to over 44,000 residents. This analysis assesses the relative effectiveness of three policy measures that could be implemented to limit saltwater intrusion into the aquifer: a cap-and-trade scheme for pumping permits, a tax on the water withdrawn, and a subsidy for industrial users not to withdraw. While each policy measure has both strengths and weaknesses in its ability to mitigate saltwater intrusion, a cap-and-trade scheme is the most feasible for the aquifer. The availability of data from the aquifer’s regulatory body, the high costs of conducting further studies, and the difficulty of measuring the numerous and extensive social and environmental externalities associated with over-extraction from the aquifer make the cap-and-trade scheme the most feasible of the three policy measures in this analysis.

More Than 8 kW Fiber Laser Amplifier with High Beam Quality Enabled by Counter Tandem Pumping Scheme

More Than 8 kW Fiber Laser Amplifier with High Beam Quality Enabled by Counter Tandem Pumping Scheme

Grid-Responsive Smart Manufacturing: Can the Manufacturing Sector Help Incorporate Renewables?

Grid-responsive smart manufacturing has the potential to contribute greatly to the use of renewable energy sources in the manufacturing sector. Smart manufacturing includes the use of demand-side management to store energy in various forms as well as schedule operations so that power is used at optimal times. This work presents a case study of a mineral manufacturing site in the United States comparing different methods of smart manufacturing integrated with renewables. Using historical utility bills and various process models, the study seeks to quantify the savings and costs of various schemes in an overall effort to improve the economics of facility operation. The models compare solar arrays, battery storage, smart pumping schemes, and various combinations of those with process-integrated technology as viable ways to reduce energy costs. The study finds that a solar array by itself is prohibitively expensive for this facility. This is due to relatively high peak demand charges and the fact that the solar array's output does not align well with the facility's real-time power usage. The addition of a battery for load shifting helps the economics significantly, bringing the payback period down from 28.4 to 17.0 years. A key finding of this study, however, is that rather than battery storage, the facility can utilize existing process flexibility, namely pumps with variable frequency drives and built-in water storage capacity, to shift loads. The combination of solar with this novel smart pumping scheme brings the payback period for this investment down to 10.2 years. The smart pumping scheme by itself, however, has a near instant payback (0.13 years), demonstrating that enhanced automation can be used to leverage existing process equipment to operate as a “battery”, but at only a fraction of the cost of an actual battery.

Generation of one-dimensional high-order Hermite-Gaussian laser beams with large mode volume

Hermite-Gaussian (HG) beams have many important applications in the optical frontier, and the limited output power of the high-purity HG beams is partly due to the small gain volume of the mode. The commonly used off-axis end-pumped scheme offers a narrow gain volume whose diameter is about a hundred microns. In this work, a new method of generating the HG beams based on a slab resonator that has a large mode volume is proposed and experimentally demonstrated. According to the optical resonator theory, the intra-cavity modes in thickness and width direction of the slab resonator are restricted by inserting two size-adjustable apertures, respectively. The one-dimensional HG beam generation is mainly guaranteed by the size of the aperture along the thickness direction of the slab, which matches the diameter of the fundamental mode. The different order one-dimensional HG beams are obtained by refined intra-cavity mode modulation. Since the higher-order modes are less sensitive to the misalignment of the cavity mirror than the lower-order modes, and the manipulation of the modes-loss at different orders is achieved by combining the tilt control of the coupled output mirror and the size control of intra-cavity apertures. By adjusting the optical gain and loss in the resonant cavity, the single mode wins the competition of laser modes. Therefore, high-purity one-dimensional HG beams with 0 to 9 orders (HG<sub>00</sub> to HG<sub>09</sub>) are generated. The pump module is comprised of a two-dimensional laser diode array which offers face-pumping to the large surface of the slab, therefore the width of the mode volume is extended to several millimeters. By further incorporating the 100mm-level long slab, the total gain volume is much larger than the counterpart in the off-axis pumping scheme. In this work, the output power of the highest order HG<sub>09</sub> mode increases up to 244 mW. Owing to the large gain volume and uniform gain distribution caused by the face-pumped slab, the purity of high order HG modes is quite good. The correlation coefficient <inline-formula><tex-math id="M3">\begin{document}$ \rho $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221422_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221422_M3.png"/></alternatives></inline-formula> between the measured intensity distribution and the theoretical value is larger than 0.95. The beam quality factor <inline-formula><tex-math id="M4">\begin{document}$ {M}^{2} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221422_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221422_M4.png"/></alternatives></inline-formula> is also in good agreement with the theoretical one. Finally, a conversion from Hermite-Gaussian beams to the donut-shaped Laguerre-Gaussian beams is realized by using an astigmatic mode converter. Hopefully, power scaling of the HG beam output is also expected by employing cascaded slab amplifiers, and the approach in this paper provides a novel solution for generation of high power HG beams.

Near-single-mode 2-kW fiber amplifier based on M-type ytterbium-doped fiber

High power fiber laser systems have attracted extensive attention due to compactness, good beam quality, efficient heat dissipation and high conversion efficiency. They are widely used in industrial processing, military, medical treatment and other fields. Over the past two decades, owing to the development of double cladding fiber and high-brightness laser diodes, the output power of fiber lasers has been greatly improved. Unfortunately, nonlinear effects (NLEs), such as stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS), restrict the further enhancement of the output power of fiber lasers. Apparently, increasing the core diameter is the most common way to suppress NLEs in the fiber, but this causes another limiting factor, i.e. mode instability (MI), resulting in the deterioration of the beam quality and in the limitation of the power scaling. Therefore, it is important and urgent to suppress the NLEs and MI simultaneously in fiber lasers. The M-type fiber, by designing refractive index profile, breaks through the stringent trade-off between mode area and numerical aperture (NA), so it possesses a larger mode area than the step index fiber, which helps to avoid NLEs and expand the power range. The M-type ytterbium doped double-clad fiber is fabricated by the modified chemical vapor deposition (MCVD) process with solution doping technology (SDT), the core/cladding diameter is 25/400 μm. The NA of high index ring and index dip in the core are 0.054 and 0.025, respectively. To test the performance of the M-type fiber during high-power operation, a 976 nm bidirectional pumped all-fiber amplifier is constructed. As a result, maximum output power of 2285 W is achieved with an optical-to-optical conversion efficiency of 66.5% under bidirectional pumping scheme, and the measured <i>M</i><sup> 2</sup> factor is 1.42, the central wavelength and 3 dB linewidth of output laser are 1080 nm and 3.01 nm, respectively. To the best of our knowledge, this is the highest output power in a continuous-wave fiber laser employing an M-type fiber at present. However, the MI effect is observed at the output power of 2252 W. The future work will focus on optimizing the structure of the M-type fiber to achieve a stabler higher-power and higher-efficiency laser output.

In-Well Pumping of a Membrane External-Cavity Surface-Emitting Laser

We present a detailed characterization and comparative study of a membrane external-cavity surface-emitting laser (MECSEL) operating in the λ = 1125-1190 nm wavelength range under in-well pumping (at 1070 nm) and barrier-pumping (at 808 nm). The slope efficiency of the laser is significantly improved from 21% with barrier-pumping to 39% when pumping only the quantum wells at 1070 nm at a heat-sink temperature of 10 °C. To address the low pump absorbance with in-well pumping, we design and implement a low-aberration multi-pass pumping scheme. An optical output power of 28.5 W and slope efficiency of ∼28% is achieved with 8 circulating passes. This represents the highest output power demonstrated in any MECSEL, as well as the highest output power in-well pumped vertical external-cavity surface-emitting laser (VECSEL). It is noted that our reported output power is only limited by the available laser input power and no thermal roll-over is observed.

Energy Efficiency Optimization in Battery-Based Photovoltaic Pumping Schemes

This article deals with the analysis of energy efficiency optimization in battery-based photovoltaic pumping schemes. The study builds on previous findings derived from the comparison between a direct photovoltaic water pumping system (DPVWPS) and the equivalent system including a lithium-ion battery (LIB). The initial experimental results of the battery-based photovoltaic water pumping system (PVWPS+LIB) were obtained with the motor-pump group operating at its rated condition of 50 Hz. In the present work, an analysis of the efficiency and the performance ratio of the variable speed drive (VSD) and the motor-pump group, showed that both parameters improve when operating in the low frequency range of the VSD and far from the rated frequency where the flow rate is maximized. Several fitting models were performed with the data obtained with the monitoring system and it was concluded that an overall energy efficiency optimization can be achieved with a VSD frequency equal to 37 Hz. A comparison of the experimental results obtained with the VSD working in the direct mode and with the battery-based solution (setting different VSD frequencies – 50 Hz, 37 Hz, and a combination of the two frequencies designed as 37/50/37 Hz) was made to determine the efficiency and performance ratios in each case. The results presented in this study also establish criteria for improving efficiencies in the LIB charging and discharging processes.

Mode-locked fiber laser of 3.5 µm using a single-walled carbon nanotube saturable absorber mirror

We report on a mid-infrared fiber laser that uses a single-walled carbon nanotube saturable absorber mirror to realize the mode-locking operation. The laser generates 3.5 µm ultra-short pulses from an erbium-doped fluoride fiber by utilizing a dual-wavelength pumping scheme. Stable mode-locking is achieved at the 3.5 µm band with a repetition rate of 25.2 MHz. The maximum average power acquired from the laser in the mode-locking regime is 25 mW. The experimental results indicate that the carbon nanotube is an effective saturable absorber for mode-locking in the mid-infrared spectral region.

Revisiting the formaldehyde masers

Context. The 4.8 GHz formaldehyde (H2CO) masers are one of a number of rare types of molecular masers in the Galaxy. There still is not agreement on the mechanism responsible for the inversion of the 110−111 transition and the conditions under which an inversion can occur, and therefore how to interpret the masers. Aims. The aim of the present calculations is to explore a larger region of parameter space to improve on our previous calculations, thereby to better understand the range of physical conditions under which an inversion of the 110−111 transition occurs. We also aim to understand recently published results that H2CO masers are radiatively pumped. Methods. We solve the rate equations of the first 40 rotational levels of o-H2CO using a fourth-order Runge-Kutta method. We consider gas kinetic temperatures between 10 and 300 K, H2 densities between 104 and 106 cm−3, and a number of different dust temperatures and grey-body spectral energy density distributions. Results. We show that when using a black body radiation field the inversion of any transition will disappear as the kinetic temperature approaches the black-body radiation temperature since the system, consisting of the gas and radiation field, approaches thermodynamic equilibrium. Using a grey-body dust radiation field appropriate for Arp 220 we find that none of 110−111, 211−212, and 312−313 transitions are inverted for kinetic temperatures less than 100 K. Our calculations also show that in theory the 110−111 transition can be inverted over a large region of explored parameter space in the presence of an external far-infrared radiation field. Limiting the abundance of H2CO to less than 10−5, however, reduces the region where an inversion occurs to H2 densities ≳105 cm−3 and kinetic temperatures ≳100 K. We propose a pumping scheme for the H2CO masers which can explain why collisions play a central role in inverting the 110−111 transition, and therefore why an external radiation field alone does not lead to an inversion. Conclusions. Collisions are an essential mechanism for the inversion of the 110−111 transition. Our results suggest that 4.8 GHz H2CO megamasers are associated with hot and dense gas typical of high mass star forming regions rather than with cold material. Although limiting the H2CO abundance to less than 10−5 significantly reduces the region in parameter space where the 110−111 is inverted, it still is not clear whether this is the only reason why these masers are so rare.

Overcoming Intensity Saturation in Nonlinear Multiple-Quantum-Well Metasurfaces for High-Efficiency Frequency Upconversion.

Engineered intersubband transitions in semiconductor heterostructures featuring multiple quantum wells (MQWs) are shown to support record-high second-order nonlinear susceptibilities. By integrating these materials in metasurfaces with tailored optical resonances, it is possible to further enhance photonic interactions, yielding giant nonlinear responses in ultrathin devices. These metasurfaces form a promising platform for efficient nonlinear processes, including frequency upconversion of low-intensity thermal infrared radiation and harmonic generation, free of phase-matching constraints intrinsic to bulk nonlinear crystals. However, nonlinear saturation at moderately large pump intensities due to the transfer of electron population into excited subbands facilitated by strongly enhanced light-matter interactions in metasurfaces fundamentally limits their overall efficiency for various nonlinear processes. Here, the saturation limits of nonlinear MQW-based metasurfaces for mid-infrared frequency upconversion are significantly extended by optimizing their designs for excitation with a strong pump coherently coupled with unpopulated upper electron subbands. This counterintuitive pumping scheme, combined with tailored material and photonic engineering of the metasurface, avoids saturation at practical levels of continuous-wave pump intensities, yielding significantly larger upconversion efficiencies than in conventional approaches. The present results open new opportunities for nonlinear metasurfaces, less limited by saturation mechanisms, with important implications for night-vision imaging and compact nonlinear wave mixingsystems.

Design of an erbium-doped Al[formula omitted] optical waveguide amplifier with on-chip integrated laser pumping source

Erbium-doped optical waveguide amplifier (EDWA) is an important building block for conventional and integrated optical communication and light signal processing systems. In recent years remarkable advancement has been achieved for EDWA to meet the demand for silicon photonic chips and integrated photonic circuits. However, in the currently demonstrated EDWAs all the laser pumping sources are external or off-chip, which not only limits the application field of EDWA, complicates the amplification scheme, but also does not fulfill the expectation of monolithic integration. In this work we propose a design of EDWA using high-gain Er-doped Al2O3 waveguide, low-loss silicon-on-insulator (SOI) waveguide, and on-chip integrated semiconductor laser pumping source. The 1550 nm signal light and 1480 nm pump light are transmitted and combined in SOI waveguide and coupled into the EDWA waveguide embedded in the adjacent layer. The 1480 nm pump light is coupled into the SOI waveguide from a bonded hybrid III–V semiconductor laser. The pump and signal waveguide building scheme, the coupling method and structure, and the integration process of laser pumping source are shown and simulated. The system performance was evaluated by using the device’s structure parameters and Er3+ rate equation model. More than 1 dB/cm net gain and up to 35 dB maximum net gain can be achieved at about 100 mW pump power. It indicates that such an on-chip integration design is feasible and fully on-chip integrated optical waveguide amplifier could be achieved.

Analysis of gain and noise characteristics of O-band Bi-doped fiber amplifier under different pumping schemes

In this paper, the gain and noise characteristics of bismuth-doped fiber amplifiers in O-band (1260–1360 nm) under forward, backward and bidirectional pumping are comprehensively compared and optimized using numerical models. The validity of the model is verified. The results show that (1)the signal power is changed within a limited range does not have an effect on the noise figure. However, the noise figure will be worse while the power continues to increase, and the magnitude of the change is most pronounced under the backward pumping scheme. With an increase in signal power from − 25 dBm to − 10 dBm, the noise figure is relatively flat under all pumping schemes. While increasing from − 10–0 dBm, the noise figure under backward pumping increased by 0.9 dB; (2)Only if pump power is below a certain threshold, the gain obtained under bidirectional scheme is significantly higher than under forward and backward.With larger pump power, the gain obtained under all pumping schemes is almost the same. With pump power less than 1.2 W, the gain under bidirectional scheme is 0.9 dB higher than that under forward and backward schemes. With more than 1.2 W, the gain difference between bidirectional and forward and backward is only 0.2 dB. The analysis provides guidance for the selection and optimization of pumping structures in BDFA, thus helping to improve the performance of O-band transmission systems.

Old frauds with a new sauce: digital assets and space transition

PurposeThe purpose of this study is to describe the evolution of fraud schemes with historically conducted with fiat money in physical space to the crypto-assets in digital space as follows: ransomware, price manipulation, pump and dump schemes, misrepresentation, spoofing and Ponzi Schemes. To explain how fraud schemes have evolved alongside digital asset markets, this study applies the space transition theory.Design/methodology/approachThe methodology used is a review of the media regarding six digital asset fraud schemes that have evolved from physical space to virtual space that are currently operational, as well as a review of the literature regarding the space transition theory.FindingsThis paper finds that the digital space and digital assets may facilitate pseudonymous criminal behavior in the present regulatory environment.Research limitations/implicationsThe field is rapidly evolving, however this study finds that the conversion from physical to virtual space obfuscates the criminal activity, facilitating anonymity of the perpetrators, and creating new challenges for the legal and regulatory environment.Practical implicationsThis paper finds that the digital space and digital assets may facilitate pseudonymous criminal behavior in the present regulatory environment. An understanding of the six crypto-asset fraud schemes described in the paper is useful for anti-financial crime professionals and regulators focusing on deterrence.Social implicationsThe space transition theory offers an explanation for why digital space leads criminals to be better positioned to conduct financial crime in virtual space relative to physical space. This offers insights into behavior of digital asset fraudster behavior that could help limit the social damage caused by crypto-asset fraud.Originality/valueTo the authors’ knowledge, this paper is the first to detail the evolution of fraud schemes with fiat money in physical space to their corresponding schemes with digital assets in physical space. This study is also the first to integrate the space transition theory into an analysis of digital asset fraud schemes.

Integrated Gallium Nitride Nonlinear Photonics

AbstractGallium nitride (GaN) as a wide bandgap material is widely used in solid‐state lighting. Thanks to its high nonlinearity and high refractive index contrast, GaN‐on‐insulator (GaNOI) is also a promising platform for nonlinear optical applications. Despite its intriguing optical proprieties, nonlinear applications of GaN are rarely studied owing to the relatively high optical loss of GaN waveguides (typically ≈2 dB cm−1). In this paper, GaNOI microresonators with intrinsic quality factor over 2.5 million are reported, corresponding to an optical loss of 0.17 dB cm−1. Parametric oscillation threshold power as low as 6.2 mW is demonstrated, and the experimentally extracted nonlinear index of GaN at telecom wavelengths is estimated to be n2 = 1.4 × 10−18 m2 W−1, which is several times larger than that of commonly used platform such as Si3N4, LiNbO3, and AlN. Single soliton generation in GaN is implemented by an auxiliary laser pumping scheme, so as to mitigate the high thermorefractive effect in GaN. The large intrinsic nonlinear refractive index, together with its broadband transparency window and high refractive index contrast, make GaNOI a promising platform for chip‐scale nonlinear applications.

Toward Peltier-cooled mid-infrared HgCdTe lasers: Analyzing the temperature quenching of stimulated emission at ∼6 μm wavelength from HgCdTe quantum wells

Despite the ultimate performance of the existing cascade lasers, simple interband emitters in the mid-infrared (IR) can still be of interest as a cheaper and widely tunable alternative for some applications. In this work, we show mid-infrared stimulated emission (SE) at 5–6 μm wavelength from an optically pumped mercury–cadmium–telluride quantum well (QW) heterostructures at temperatures up to 200 K. At lower temperatures, the SE threshold appears to be mostly determined by conventional eeh Auger recombination, while the contribution of alternative QW-specific ehh Auger processes is limited. At higher temperatures, we establish heating of the electron gas by pumping radiation as a primary factor responsible for the thermal quenching of the SE. Consequently, both pumping scheme and QW designs should be carefully revised to minimize carrier heating in order to realize near-to-mid-IR optical converters operating close to ambient temperature. We suggest using low-barrier QWs to minimize excessive heat introduced in the QW upon carrier capture and also to eliminate eeh Auger processes involving excited QW subbands. Thus, mid-infrared HgCdTe lasers are expected to reach operating temperatures readily attainable under thermoelectric cooling.