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High-speed modulation of a terahertz quantum cascade laser by coherent acoustic phonon pulses
摘要： The fast modulation of lasers is a fundamental requirement for applications in optical communications, high-resolution spectroscopy and metrology. In the terahertz-frequency range, the quantum-cascade laser (QCL) is a high-power source with the potential for high-frequency modulation. However, conventional electronic modulation is limited fundamentally by parasitic device impedance, and so alternative physical processes must be exploited to modulate the QCL gain on ultrafast timescales. Here, we demonstrate an alternative mechanism to modulate the emission from a QCL device, whereby optically-generated acoustic phonon pulses are used to perturb the QCL bandstructure, enabling fast amplitude modulation that can be controlled using the QCL drive current or strain pulse amplitude, to a maximum modulation depth of 6% in our experiment. We show that this modulation can be explained using perturbation theory analysis. While the modulation rise-time was limited to ~800 ps by our measurement system, theoretical considerations suggest considerably faster modulation could be possible.
关键词： terahertz,quantum-cascade laser,modulation,acoustic phonon,ultrafast
更新于2025-09-19 17:13:59
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Gas chromatography vs. quantum cascade laser-based??N <sub/>2</sub> O flux measurements using a novel chamber design
摘要： Recent advances in laser spectrometry offer new opportunities to investigate the soil–atmosphere exchange of nitrous oxide. During two field campaigns conducted at a grassland site and a willow field, we tested the performance of a quantum cascade laser (QCL) connected to a newly developed automated chamber system against a conventional gas chromatography (GC) approach using the same chambers plus an automated gas sampling unit with septum capped vials and subsequent laboratory GC analysis. Through its high precision and time resolution, data of the QCL system were used for quantifying the commonly observed nonlinearity in concentration changes during chamber deployment, making the calculation of exchange fluxes more accurate by the application of exponential models. As expected, the curvature values in the concentration increase was higher during long (60 min) chamber closure times and under high-flux conditions (FN2O > 150 μg N m?2 h?1) than those values that were found when chambers were closed for only 10 min and/or when fluxes were in a typical range of 2 to 50 μg N m?2 h?1. Extremely low standard errors of fluxes, i.e., from ～ 0.2 to 1.7 % of the flux value, were observed regardless of linear or exponential flux calculation when using QCL data. Thus, we recommend reducing chamber closure times to a maximum of 10 min when a fast-response analyzer is available and this type of chamber system is used to keep soil disturbance low and conditions around the chamber plot as natural as possible. Further, applying linear regression to a 3 min data window with rejecting the first 2 min after closure and a sampling time of every 5 s proved to be sufficient for robust flux determination while ensuring that standard errors of N2O fluxes were still on a relatively low level. Despite low signal-to-noise ratios, GC was still found to be a useful method to determine the mean the soil–atmosphere exchange of N2O on longer timescales during specific campaigns. Intriguingly, the consistency between GC and QCL-based campaign averages was better under low than under high N2O efflux conditions, although single flux values were highly scattered during the low efflux campaign. Furthermore, the QCL technology provides a useful tool to accurately investigate the highly debated topic of diurnal courses of N2O fluxes and its controlling factors. Our new chamber design protects the measurement spot from unintended shading and minimizes disturbance of throughfall, thereby complying with high quality requirements of long-term observation studies and research infrastructures.
关键词： gas chromatography,soil–atmosphere exchange,chamber design,nitrous oxide,quantum cascade laser,flux measurements
更新于2025-09-19 17:13:59
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Applicability of a gas analyzer with dual quantum cascade lasers for simultaneous measurements of N2O, CH4 and CO2 fluxes from cropland using the eddy covariance technique
摘要： We evaluated the applicability of a closed-path gas analyzer with two mid-infrared quantum cascade lasers (QCLs) for simultaneous measurement of nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) fluxes from a cropland using the eddy covariance (EC) technique. The measurements were carried out in a typical vegetable field in the subtropical China during the wintertime, when the gas fluxes are at their lowest level in the year. A new approach was proposed to optimize the determination of lag times between the wind and gas concentration data, which was proven efficient to increase the reliability of the measured fluxes when the gas exchanges are weak. The dual-QCL analyzer showed a median precision (1σ) of 0.14 nmol mol?1 for N2O, 3.3 nmol mol?1 for CH4 and 0.36 μmol mol–1 for CO2 at sampling frequency of 10 Hz under the field conditions. Such precisions are better than, or comparable with, those of other commonly used closed-path or open-path gas analyzers, which are capable of measuring only one or two of the three gases. The detection limit of the EC system for measuring half-hourly fluxes were 0.05 nmol m?2 s?1 for N2O, 1.12 nmol m?2 s?1 for CH4 and 0.14 μmol m–2 s–1 for CO2. The results showed that 100% of the N2O, 87% of the CH4 and 96% of the CO2 fluxes were larger than the above detection limits. This study suggests that the EC technique using a closed-path gas analyzer with two quantum cascade lasers is qualified for reliable and simultaneous measurements of N2O, CH4 and CO2 fluxes from a subtropical cropland throughout the year. Moreover, EC method based on this type of gas analyzer provides an additional option for long-term and simultaneous flux measurements of the three greenhouse gases in a wide range of agricultural and natural ecosystems.
关键词： Nitrous oxide,eddy covariance,cropland,methane,flux,quantum cascade laser,carbon dioxide
更新于2025-09-19 17:13:59
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High-power (>1 W) room-temperature quantum-cascade lasers for the long-wavelength IR region
摘要： Ridge quantum-cascade lasers emitting at a wavelength near 8 mm are fabricated and studied. Lasing at room temperature with a maximum output peak power exceeding 1 W from one facet is demonstrated.
关键词： high power,quantum-cascade laser,heterostructure
更新于2025-09-19 17:13:59
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Electron Population Dynamics in Optically Pumped Asymmetric Coupled Ge/SiGe Quantum Wells: Experiment and Models
摘要： n-type doped Ge quantum wells with SiGe barriers represent a promising heterostructure system for the development of radiation emitters in the terahertz range such as electrically pumped quantum cascade lasers and optically pumped quantum fountain lasers. The nonpolar lattice of Ge and SiGe provides electron–phonon scattering rates that are one order of magnitude lower than polar GaAs. We have developed a self-consistent numerical energy-balance model based on a rate equation approach which includes inelastic and elastic inter- and intra-subband scattering events and takes into account a realistic two-dimensional electron gas distribution in all the subband states of the Ge/SiGe quantum wells by considering subband-dependent electronic temperatures and chemical potentials. This full-subband model is compared here to the standard discrete-energy-level model, in which the material parameters are limited to few input values (scattering rates and radiative cross sections). To provide an experimental case study, we have epitaxially grown samples consisting of two asymmetric coupled quantum wells forming a three-level system, which we optically pump with a free electron laser. The benchmark quantity selected for model testing purposes is the saturation intensity at the 1→3 intersubband transition. The numerical quantum model prediction is in reasonable agreement with the experiments and therefore outperforms the discrete-energy-level analytical model, of which the prediction of the saturation intensity is off by a factor 3.
关键词： silicon–germanium heterostructures,intersubband photoluminescence,optical pumping,intersubband transitions,electron–phonon interaction,infrared spectroscopy,quantum wells,free electron laser,terahertz quantum cascade laser
更新于2025-09-16 10:30:52
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - <sup>15</sup> NH <sub/>3</sub> terahertz gas laser pumped by a mid-infrared quantum-cascade laser
摘要： We present an optically pumped terahertz gas laser, which is based on a distributed-feedback mid-infrared quantum-cascade laser as a pump source, a standing wave resonator, and 15NH3 as a gain medium.
关键词： optical pumping,15NH3,terahertz gas laser,mid-infrared,quantum-cascade laser
更新于2025-09-16 10:30:52
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Investigation of Chaotic and Spiking Dynamics in Mid-Infrared Quantum Cascade Lasers Operating Continuous-Waves and Under Current Modulation
摘要： This study investigates chaotic and spiking dynamics of mid-infrared quantum cascade lasers operating under external optical feedback and emitting at 5.5 μm and 9 μm. In order to deepen the understanding, the route to chaos is experimentally studied in the case of continuous-wave and current modulation operation. The non-linear dynamics are analyzed with bifurcation diagrams. While for quasi-continuous wave operation, chaos is found to be more complex, pure continuous wave pumping always leads to the generation of a regular spiking induced low-frequency ?uctuations dynamics. In the latter, results show that by combining external optical feedback with periodic forcing and further induced current modulation allows a better control of the chaotic dropouts. This work provides a novel insight into the development of future secure free-space communications based on quantum cascade lasers or unpredictable optical countermeasure systems operating within the two transparency atmospheric windows hence between 3 μm–5 μm and 8.5 μm–11 μm.
关键词： entrainment phenomenon,quantum cascade laser,secure communications,external optical feedback,mid-infrared photonics,Nonlinear dynamics
更新于2025-09-16 10:30:52
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - High-resolution frequency and phase control of a terahertz laser
摘要： We report on the high-resolution frequency and phase control of a terahertz (THz) quantum cascade laser (QCL). The 2.0 THz QCL is locked to a stable microwave reference frequency via an all-fibre infrared frequency comb. The frequency of the QCL is controlled by optical injection and the phase is independently controlled by introducing a phase-lock loop that provides electronic feedback to the QCL, forming an optical injection phase locked loop (OIPLL). By implementing this, (1) the instrument limited linewidth of the locked QCL was <1Hz (2) for a fixed frequency, the phase of the THz QCL relative to the microwave reference frequency can be controlled within a range 0.3(cid:2).
关键词： optical injection phase locked loop,phase control,quantum cascade laser,frequency control,terahertz
更新于2025-09-16 10:30:52
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Electromagnetic-field analysis of diagonal-feedhorn antennas for terahertz-frequency quantum-cascade laser integration
摘要： we present an electromagnetic-field analysis of a terahertz-frequency quantum-cascade (THz QCL) integrated with a mechanically micro-machined waveguide cavity and diagonal feedhorn. A hybrid finite-element/Fourier transform approach enables analysis of both the near-field and far-field regions and is shown to agree well with experimental observations. The far-field antenna patterns show enhancement of the beam profile when compared with an unmounted QCL, in terms of beam divergence and side-lobe suppression ratio. Furthermore, we demonstrate integration of the QCL with dual diagonal feedhorns, enabling simultaneous access to both facets of the QCL, underpinning future integration with a satellite-based receiver and frequency-stabilization subsystem.
关键词： terahertz-frequency quantum-cascade laser,waveguide cavity,beam profile enhancement,electromagnetic-field analysis,diagonal feedhorn
更新于2025-09-16 10:30:52
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Dispersion and Ridge Width Effect in Terahertz Quantum Cascade Laser Combs
摘要： We systematically investigate the laser ridge width effect on comb operation of single plasmon waveguide quantum cascade lasers emitting around 4.2 THz. The total group velocity dispersion (GVD), including gain, waveguide, and material dispersions, is numerically evaluated for 6-mm-long lasers with ridge widths varying from 100 to 200 μm. The simulation reveals that the clamped gain dispersion strongly contributes to the total GVD and the laser with a 150-μm-wide ridge shows the flattest total GVD in the lasing range between 4.05 and 4.35 THz. The optimal ridge width of 150 μm for comb operation is also experimentally verified.
关键词： group velocity dispersion,frequency comb,quantum cascade laser,ridge width,terahertz
更新于2025-09-16 10:30:52