Mid-infrared Laser Research Articles

Jamming Effectiveness of Mid-infrared Lasers on the Quaternary Cross-shaped Detector

With the development of infrared guidance technology, the guidance accuracy and anti-jamming ability of infrared guided missile are improved constantly. Based on the analysis of the mechanism of the third generation quaternary cross-shaped detector and the influence of jamming signals on the target recognition, the detector model and the mid-infrared laser interference model based on the time-domain feature analysis are established in this paper. According to the simulation results, we use the continuous and pulsed mid-infrared laser to experiment the jamming effectiveness of the quaternary cross-shaped detector. It is found that compared with continuous mid-infrared laser, pulsed mid-infrared laser is easier to make the detector lose the target and difficult to recover the tracking.

Methane, Ethylene, and Ethane Detection by Differential Helmholtz Resonance Spectroscopy Using a 3345 nm Mid-Infrared Tunable Diode Laser Source

Gas detection based on photoacoustic spectroscopy (PAS) has attracted extensive attention due to its high sensitivity and large range of linearity. Herein, to achieve the simultaneous detection of the light carbon gases (CH4, C2H4, and C2H6), a gas detection system was constructed using a single mid-infrared tunable diode laser (central wavelength 3345 nm) source based on differential Helmholtz resonance spectroscopy (DHRS). The detection parameters (driving current, modulation depth, phase angle, etc.) were optimized under ambient pressure using the 1f demodulation method. With an integration time of 2 s, the detection limit reached 98.8 ppb, 252 ppb, and 33 ppb for methane, ethylene, and ethane, respectively. The validation test of the three-component mixture shows that the cross-interference can be effectively reduced by multiwavelength linear regression, and single wavelength linear regression causes large errors in the quantification of methane and ethylene.

Influence of Nd3+ concentration on mid-infrared emission in PbF2 crystal co-doped with Ho3+ and Nd3+ ions

A promising series of HoyNdxPb(1–x–y)F2 (x = 0, 0.01, 0.02, 0.03, 0.04; y = 0.02) crystals was grown by the Bridgman method. The influence of the Nd3+ ions concentration on mid-infrared (∼2.0, ∼2.9 and ∼3.9 μm) fluorescence emissions of Ho3+ ions in the PbF2 crystal excited by 808 nm laser diode was investigated in this work. The energy transfer mechanism between Nd3+ ions and Ho3+ ions under different concentrations of the Nd3+ ions was systematically analyzed. The results show that the Nd3+ ions have good sensitization and deactivation effect on the Ho3+ ions to stimulate the mid-infrared fluorescence emissions. The experimental analysis proves that the sensitization efficiency of the Nd3+ ions is relatively stable at around 93.45% with varying Nd3+-doping concentrations. Concentration dependence studies indicate that the concentration of the Nd3+ ions has significant influence on mid-infrared emissions. When the doping concentration of the Nd3+ ions is up to 2.0 at%, the intensity of ∼2.0, ∼2.9 and ∼3.9 μm emissions all reach the maximum. The output characteristics of a 3.9 μm laser are simulated, and it is found that with the increase of the Nd3+-doping concentration, the peak power, pulse width, and peak energy all meet the trend of first increasing and then decreasing, and Ho0.02Nd0.02Pb0.96F2 crystal displays the best performance. All the results show that the Nd3+/Ho3+ co-doped PbF2 crystals might act as a useful optical medium for mid-infrared laser applications.

Thermal Lensing and Laser-Induced Damage in Special Pure Chalcogenide Ge35As10S55 and Ge20As22Se58 Glasses under Quasi-CW Fiber Laser Irradiation at 1908 nm

Special pure chalcogenide glass is the material of choice for many mid-infrared optical fibers and fiber lasers. In this paper, the thermo-optical lensing and laser-induced damage were studied in Ge35As10S55 and Ge20As22Se58 glasses and compared with the well-studied As2S3 glass. The thermal Z-scan technique with the quasi-CW Tm-doped fiber laser at 1908 nm was applied to study thermal lensing in chalcogenide glass. The laser-induced damage of various chalcogenide glasses was determined using the one-on-one procedure. The thermal nonlinear refractive index of the Ge35As10S55 and Ge20As22Se58 glasses was found to be lower than that of the As2S3 glass. The laser-induced damage threshold of the Ge20As22Se58 glass was determined to be higher than that of the Ge35As10S55 glass. The difference in the thermal damage threshold of the Ge35As10S55 and Ge20As22Se58 glasses and their lower value in comparison with the As2S3 glass were explained by a deviation from the stoichiometry of glass compositions and their tendency to crystallize.

Performance simulation of an InGaSb/GaSb based quantum well structure for laser diode applications

The present study reports the impact of structural parameters on optoelectronic properties of InGasb/GaSb based quantum well structures (Qws). The laser diodes are designed to operate at 2.3 μm at 300 K. Numerical calculations of the emission wavelength, optical and modal gain of TE mode in InGaSb/GaSb laser diode structure have been carried out for various well material compositions, well thickness, number of quantum wells and temperature. The optical confinement factor and threshold current density are also simulated and reported. The calculations were performed using the 8-bands k.p model. For an injected carrier concentration of 1.56 × 1018 cm−3 at 300 K, peak gain value of the order of 1400 cm−1 is reached and a modal gain of 94 cm−1 can be obtained. A threshold current density around 3 kA/cm2, is expected to be obtained through optical losses of about 50 cm−1. The results show that InGaSb/GaSb quantum wells are appropriate for mid-infrared lasers operating at 300 K.

Large mode-area all-solid anti-resonant fiber based on chalcogenide glass for mid-infrared transmission.

A large mode-area chalcogenide all-solid anti-resonant fiber has been designed and successfully prepared for the first time. The numerical results show that the high-order mode extinction ratio of the designed fiber can reach 6000, and the maximum mode-area is 1500 um2. The fiber possesses a calculated low bending loss of less than 10-2 dB/m as the bending radius is larger than 15 cm. In addition, there is a low normal dispersion of -3 ps/nm/km at 5 μm, which is beneficial for the transmission of high power mid-infrared laser. Finally, a completely structured all-solid fiber was prepared by the precision drilling and two-stage rod-in-tube methods. The fabricated fibers transmit in the mid-infrared spectral range from 4.5 to 7.5 μm with the lowest loss of 7 dB/m @ 4.8 μm. Modeling suggests that the theoretical loss of the optimized structure is consistent with that of the prepared structure in the long wavelength band.

Nitromethane as a nitric oxide precursor for studying high-temperature interactions between ammonia and nitric oxide in a shock tube

Ammonia (NH3) is a promising carbon-free fuel for carbon neutrality that has recently received increasing attention. However, NOx emissions are one of the main problems for NH3 or NH3-blended combustion. This study used nitromethane (CH3NO2) as a nitric oxide precursor to study NH3/NO interactions at high temperatures. The temperature, CO, CO2, NO, and NH3 time-histories were measured simultaneously during the pyrolysis and oxidation (equivalence ratios ϕ = 2.0 and 1.0) of CH3NO2 and CH3NO2/NH3 mixtures behind reflected shock waves using mid-infrared laser absorption spectroscopy to analyze the NH3/NO interactions. The measurements were used to validate and evaluate seven kinetic models which gave very different predictions for the different mixtures, among which the Glarborg et al. (2018) and Shang et al. (2020) models agreed best with the temperature, NO, and NH3 measurements. The measured CO and CO2 time-histories are shown in the Supplementary Material. Both mechanisms accurately capture the temperature plateau while the main difference is the temperature increase during oxidation. The NO formation rate and plateau concentrations during CH3NO2 pyrolysis are better predicted by the Shang model than by the Glarborg model. Both mechanisms capture the NO formation rate for CH3NO2 oxidation with ϕ = 2.0 but underestimate it for ϕ = 1.0. With NH3, the Glarborg model better predicts the NO removal during CH3NO2/NH3 pyrolysis. However, both mechanisms underestimate the NO formation rate and maximum but overestimate the NO removal rate and NH3 consumption for CH3NO2/NH3 oxidation. Rate-of-production and sensitivity analyses show that: for the NO formation, CH3 + NO2 = CH3O + NO and NO2 + H = NO + OH are the primary pathways and CH3NO2 (+ M) = CH3 + NO2 (+ M) is the most sensitive reaction. NH3 + OH = NH2 + H2O contributes the most to the NH3 consumption during CH3NO2/NH3 pyrolysis, while NH3 + H = NH2 + H2 and NH3 + O = NH2 + OH are increasingly important at oxidation condition. NH2 + NO = N2 + H2O and NH2 + NO = NNH + OH are the most important reactions for the NO reduction with NH3 existing. The rate constants of some key reactions were revised to improve the predictions.

Uniaxial Strain-Induced Tunable Mid-infrared Light Emission from Thin Film Black Phosphorus.

Strain engineering is a powerful tool that can modulate semiconductor device performance. Here, we demonstrate that the bandgap of thin film (∼40 nm) black phosphorus (bP) can be continuously tuned from 2.9 to 3.9 μm by applying an in-plane uniaxial strain, as evidenced by mid-infrared photoluminescence (PL) spectroscopy. The deduced bandgap strain coefficients are ∼103 meV %-1, which coincide with those obtained in few-layer bP. On the basis of first-principles calculations, the origin of the uniaxial tensile strain-induced PL enhancement is suggested to be due to the increase in both the effective mass ratio (me*/mh*) and the bandgap, leading to the increment of the radiative efficiency. Moreover, the mid-infrared PL emission remains perfectly linear-polarized along the armchair direction regardless of tensile or compressive strain. The highly tunable bandgap of bP in the mid-infrared regime opens up opportunities for the realization of mid-infrared light-emitting diodes and lasers using layered materials.

Ultra-small low-threshold mid-infrared plasmonic nanowire lasers based on n-doped GaN

An ultra-small mid-infrared plasmonic nanowire laser based on n-doped GaN metallic material is proposed and studied by the finite-difference time-domain method. In comparison with the noble metals, nGaN is found to possess superior permittivity characteristics in the mid-infrared range, beneficial for generating low-loss surface plasmon polaritons and achieving strong subwavelength optical confinement. The results show that at a wavelength of 4.2 µm, the penetration depth into the dielectric is substantially decreased from 1384 to 163 nm by replacing Au with nGaN, and the cutoff diameter of nGaN-based laser is as small as 265 nm, only 65% that of the Au-based one. To suppress the relatively large propagation loss induced by nGaN, an nGaN/Au-based laser structure is designed, whose threshold gain has been reduced by nearly half. This work may pave the way for the development of miniaturized low-consumption mid-infrared lasers.

Design and fabrication of a chalcogenide hollow-core anti-resonant fiber for mid-infrared applications.

Chalcogenide hollow-core anti-resonant fibers (HC-ARFs) are a promising propagation medium for high-power mid-infrared (3-5 µm) laser delivery, while their properties have not been well understood and their fabrications remain challenging. In this paper, we design a seven-hole chalcogenide HC-ARF with touching cladding capillaries, which was then fabricated from purified As40S60 glass by combining the "stack-and-draw" method with a dual gas path pressure control technique. In particular, we predict theoretically and confirm experimentally that such medium exhibits higher-order mode suppression properties and several low-loss transmission bands in the mid-infrared spectrum, with the measured fiber loss being as low as 1.29 dB/m at 4.79 µm. Our results pave the way for the fabrication and implication of various chalcogenide HC-ARFs in mid-infrared laser delivery systems.

Fabrication, microstructure and mid-infrared luminescence of Er:(ScxY1-x)2O3 transparent ceramics

Compositionally “mixed” (yttria-scandia) sesquioxide transparent ceramics doped with erbium ions, ∼7 at.% Er:(ScxY1-x)2O3 (where x = 0–0.445) were fabricated by vacuum sintering at 1750 °C for 5 h using 1.7 mol% ZrO2 as a sintering additive. For this, nanopowders of the same composition obtained by laser ablation and sedimentation were used. The as-prepared nanoparticles (monoclinic sp. gr. C2/m) had a mean size of 20 nm and they were transformed into the stable cubic phase by calcination at 870–1150 °C. The ceramics were of single-phase nature (C-type bixbyite structure, sp. gr. Ia-3). For the (Er0.074Sc0.114Y0.812)2O3 ceramic, the lattice constant was a = 10.5067 Å, the mean grain size – 21.6 μm, the average content of pores – 4.2 ppm and the transmission at 1.1 μm - 81.9%. The X-ray diffraction and Raman studies of ceramics confirmed the existence of a solid-solution composition. With increasing the Sc3+ content in the ceramics, their lattice shrinked, the mean grain size increased and the thermal conductivity decreased from 6.14 to 3.66 Wm−1K−1 at room temperature. The “mixed” ceramics exhibited intense inhomogeneously broadened emission around 2.8 μm making them promising for mid-infrared lasers.

High-quality factor mid-infrared absorber based on all-dielectric metasurfaces.

The absorption spectrum of metasurface absorbers can be manipulated by changing structures. However, narrowband performance absorbers with high quality factors (Q-factor) are hard to achieve, mainly for the ohmic loss of metal resonators. Here, we propose an all-dielectric metasurface absorber with narrow absorption linewidth in the mid-infrared range. Magnetic quadrupole resonance is excited in the stacked Ge-Si3N4 nanoarrays with an absorption of 89.6% and a Q-factor of 6120 at 6.612 µm. The separate lossless Ge resonator and lossy Si3N4 layer realize high electromagnetic field gain and absorption, respectively. And the proposed method successfully reduced the intrinsic loss of the absorber, which reduced the absorption beyond the resonant wavelength and improved the absorption efficiency of Si3N4 in the low loss range. Furthermore, the absorption intensity and wavelength can be modulated by adjusting the geometric parameters of the structure. We believe this research has good application prospects in mid-infrared lasers, thermal emitters, gas feature sensing, and spectral detection.

Design of a megawatt superradiant terahertz source for FELiChEM

FELiChEM is an infrared free electron laser user facility built at the University of Science and Technology of China (USTC). It consists of two free electron laser oscillators which produce mid-infrared and far-infrared lasers covering the spectral range of 2–200 μm at current stage. In this paper, we propose a new operation mode of a megawatt (MW) terahertz (THz) superradiance free electron laser (FEL) for FELiChEM. Start-to-end (S2E) simulations have been carried out, in which the three-dimension particle-in-cell (PIC) code PUFFIN is used for the generation of the THz superradiance. Simulation results demonstrate that this superradiant FEL can provide 100–1000 μm laser with MW-class peak power from a 1.2 meter single-pass undulator when the electron energy is around 15 MeV.

Frequency combs in quantum cascade lasers: An overview of modeling and experiments

Over the past decade, the demonstration of frequency combs has been reported in a wide range of quantum cascade lasers. These combs have huge potential in applications, including spectroscopy, sensing, imaging, and communication domains. In this perspective review, we explore the modeling and experimental state of the art on frequency combs in mid-infrared and terahertz quantum cascade lasers, 10 years since the first demonstrations that these devices can spontaneously generate combs.

Amplification of GaSb-Based Diode Lasers in an Erbium-Doped Fluoride Fibre Amplifier

Building upon recent advances in GaSb-based diode lasers and Er-doped fluoride fibre technologies, this article demonstrates for the first time the fibre-based amplification of mid-infrared diode lasers in the wavelength range around 2.78 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m. The laser setup consists of a GaSb-based diode laser and a single-stage Er-doped fibre amplifier. Amplification is investigated for continuous wave (CW) and ns-pulsed input signals, generated by gain-modulation of the GaSb-based seed lasers. The experimental results include the demonstration of output powers up to 0.9 W, pulse durations as short as 20 ns, and pulse repetition rates up to 1 MHz. Additionally, the amplification of commercial and custom-made GaSb-based seed lasers is compared and the impact of different fibre end-cap materials on laser performance is analysed.

In situ probing of atmospheric-pressure warm air glow discharge for nitrogen fixation by multiple laser spectroscopies

The fixation of atmospheric nitrogen into valuable compounds through reactive plasma processes has attracted intense interests due to its easy operation and compatibility with distributed renewable energy sources. However, practical implementation of plasma-assisted nitrogen fixation is hampered because of its relatively low throughput, which is dominantly limited by the unclear underlying mechanisms. In this study, effort was focused on the in situ production of key species in a DC-driven warm air glow discharge at atmospheric pressure with the help of advanced laser spectroscopic diagnostics. Laser Rayleigh scattering was applied to determine the gas temperature distribution in the discharge column. And mid-infrared quantum cascade laser absorption spectroscopy and one/two-photon absorption laser-induced fluorescence were performed on molecular nitric oxide (NO), atomic oxygen and nitrogen (O, N) for their absolute densities in the discharge. It is found that the spatial distributions of gas temperature, O and N atoms show peaks in the hot discharge center. In contrast, a hollow ‘doughnut’ shape characterized by the NO molecule was observed, particularly under conditions of high discharge current but low airflow rate. The steady-state simulation shows that the hollow pattern of NO is dominantly induced by the radial diffusion of species due to the steep spatial gradient of gas temperature in the discharge cross-section. Moreover, the reverse conversion by atomic N leads to a negative effect on the NO synthesis, especially at the discharge center where the N density and gas temperature are high. From the steady-state modeling, a similar hollow distribution of NO2 was depicted in the air glow discharge. These results demonstrate the strong dependence on atomic O for the major formation process of NO, and the importance of suppressing the reverse paths dominated by atomic N for higher NO production in the studied warm air plasma.

Fluorescence and Physical Properties of Tm3+/Ho3+ Co-Doped Tellurite Glasses for Mid-Infrared Laser

In this work, a series of Tm3+/Ho3+ co-doped tellurite glasses were successfully prepared by the melt-quenching method. The spectroscopic properties around 2 μm of Tm3+/Ho3+ co-doped tellurite glasses were studied under 808 nm laser excitation. Based on the Judd-Ofelt theory, the phenomenological intensity parameters Ω t (t = 2, 4, 6) of the Tm3+/Ho3+ co-doped tellurite glasses were calculated. In addition, the emission cross-section and the gain coefficient of Ho3+ were calculated, and the maximum values are 0.76 × 10−20 cm−1 and 1.38 cm−1, respectively. These results portend that the Tm3+/Ho3+ co-doped tellurite glass has excellent spectroscopic properties and attractive laser performance in mid-infrared waveband.

High-efficiency mid-infrared InGaAs/InP arrayed waveguide gratings.

Photonic integrated circuits and mid-infrared quantum cascade lasers have attracted significant attention over the years because of the numerous applications enabled by these compact semiconductor chips. In this paper, we demonstrate low loss passive waveguides and highly efficient arrayed waveguide gratings that can be used, for example, to beam combine infrared (IR) laser arrays. The waveguide structure used consists of an In0.53Ga0.47As core and InP cladding layers. This material system was chosen because of its compatibility with future monolithic integration with quantum cascade lasers. Different photonic circuits were fabricated using standard semiconductor processes, and experiments conducted with these chips demonstrated low-loss waveguides with an estimated propagation loss of ∼ 1.2 dB/cm as well as micro-ring resonators with an intrinsic Q-factor of 174,000. Arrayed waveguide gratings operating in the 5.15-5.34 µm range feature low insertion loss and non-uniformity of ∼ 0.9 dB and ∼ 0.6 dB, respectively. The demonstration of the present photonic circuits paves the path toward monolithic fabrication of compact infrared light sources with advanced functionalities beneficial to many chemical sensing and high-power applications.

Ultrastrong Optical Harmonic Generations in Layered Platinum Disulfide in the Mid-Infrared.

Nonlinear optical activities (e.g., harmonic generations) in two-dimensional (2D) layered materials have attracted much attention due to the great promise in diverse optoelectronic applications such as nonlinear optical modulators, nonreciprocal optical device, and nonlinear optical imaging. Exploration of nonlinear optical response (e.g., frequency conversion) in the infrared, especially the mid-infrared (MIR) region, is highly desirable for ultrafast MIR laser applications ranging from tunable MIR coherent sources, MIR supercontinuum generation, and MIR frequency-comb-based spectroscopy to high harmonic generation. However, nonlinear optical effects in 2D layered materials under MIR pump are rarely reported, mainly due to the lack of suitable 2D layered materials. Van der Waals layered platinum disulfide (PtS2) with a sizable bandgap from the visible to the infrared region is a promising candidate for realizing MIR nonlinear optical devices. In this work, we investigate the nonlinear optical properties including third-and fifth-harmonic generation (THG and FHG) in thin layered PtS2 under infrared pump (1550-2510 nm). Strikingly, the ultrastrong third-order nonlinear susceptibility χ(3)(-3ω;ω,ω,ω) of thin layered PtS2 in the MIR region was estimated to be over 10-18 m2/V2, which is about one order of that in traditional transition metal chalcogenides. Such excellent performance makes air-stable PtS2 a potential candidate for developing next-generation MIR nonlinear photonic devices.

Numerical simulation and observed rotational relaxation in CW and pulsed HBr-filled hollow-core fiber lasers.

Gas-filled hollow-core fiber (HCF) lasers have emerged as a promising technology for generating mid-infrared lasers. A four-energy level system laser model is presented to predict the performance of optically pumped HBr-filled HCF lasers under continuous wave (CW) and pulsed excitations. The steady state condition is considered in CW pumping and the characteristics of simulated population density and power distribution along HCF are investigated. The finite-difference time-domain method is employed in pulsed pumping and the simulated evolutions of pump pulse and laser pulse at different positions along the HCF are studied. In addition, the phenomena of rotational relaxation in HBr-filled HCF lasers are investigated experimentally for the first time, to the best of our knowledge, showing that using the absorption lines away from the strongest absorption lines and tuning the pump wavelength deviating from the center of the absorption line makes the rotational relaxation occur easily. The demonstration is conductive to reveal the underlying mechanism of such gas-filled HCF lasers.