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[IEEE 2018 IEEE International Ultrasonics Symposium (IUS) - Kobe, Japan (2018.10.22-2018.10.25)] 2018 IEEE International Ultrasonics Symposium (IUS) - Fast SAW Device Simulation in COMSOL Using the Hierarchical Cascading Method
摘要： Using the hierarchical cascading method for modeling semiconductor devices makes it possible to achieve high accuracy by considering the influence of the details of the structure of the device. In this paper, we consider the simulation of a quantum cascade laser (QCL) with a periodic structure. The simulation is performed using the finite element method (FEM) in the COMSOL Multiphysics software. The results show that the proposed method allows to obtain the characteristics of the device with high accuracy.
关键词： finite element method,quantum cascade laser,COMSOL Multiphysics,simulation
更新于2025-09-23 15:23:52
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Terahertz generation in quantum-cascade lasers through down-conversion optical nonlinearity: Design and modeling
摘要： In this paper, we propose an electrically driven optically excited laser structure for terahertz (THz) generation in quantum cascade lasers (QCLs) through frequency down-conversion optical nonlinearity. In our distinct design, both the pump and THz radiations are generated simultaneously by optical and electronic intersubband transitions (ISTs) between the quantized states within the conduction band of the same active region of a QCL. The modeling of laser bandstructure is achieved using a self-consistent solution of Schrodinger-Poisson equations, and the detailed analysis of electronic transport of the proposed structure is performed using the density matrix approach and energy-density balance equation that self-consistently consider the optical, electrical and thermal interactions in the structure. Additionally, the waveguide loss for the THz optical mode is considered using the bulk Drude model. Using a stationary solution of the density matrix equations, an expression for the THz intensity gain is derived as a function of pump field intensity, carrier distributions and quantum coherence contributions. Using the presented model, we analyze the steady-state and transient characteristics of the device for two different heatsink temperatures, 220 and 300 K. Simulation results show that the proposed structure has a potential to generate room-temperature THz radiation in QCLs.
关键词： Quantum-cascade laser (QCL),terahertz (THz) generation,down-conversion optical nonlinearity,density-matrix formalism
更新于2025-09-23 15:21:01
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Wideband electrically-controlled Vernier frequency tuneable terahertz quantum cascade laser
摘要： Frequency tuning in terahertz frequency quantum cascade lasers is challenging because of low thermal and current tuning coefficients. Moreover, photonic designs like Vernier selection based sampled gratings, used in telecom lasers to tune emission frequency, are unsuitable due to the long terahertz wavelengths and will require impractically long cavities (>15 mm). Here, we report the first wideband frequency tuning from a monolithic device exploiting Vernier selection rules using a coupled-cavity laser with a defect engineered photonic lattice. A precisely positioned defect lattice allows us to engineer the free spectral range and finesse of one of the cavities, similar to a sampled grating but using shorter cavity lengths (<4mm). A coupled-cavity was used to tune the emission frequency. We achieve frequency tuning over 209 GHz, including mode-hop-free continuous tuning of ~6–21 GHz across six frequency bands, controlled through Stark shift, cavity-pulling, localized Joule heating and thermal effects.
关键词： quantum cascade laser,Terahertz,frequency tuning
更新于2025-09-23 15:21:01
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Quantum cascade laser based hybrid dual comb spectrometer
摘要： Four-wave-mixing-based quantum cascade laser frequency combs (QCL-FC) are a powerful photonic tool, driving a recent revolution in major molecular fingerprint regions, i.e. mid- and far-infrared domains. Their compact and frequency-agile design, together with their high optical power and spectral purity, promise to deliver an all-in-one source for the most challenging spectroscopic applications. Here, we demonstrate a metrological-grade hybrid dual comb spectrometer, combining the advantages of a THz QCL-FC with the accuracy and absolute frequency referencing provided by a free-standing, optically-rectified THz frequency comb. A proof-of-principle application to methanol molecular transitions is presented. The multi-heterodyne molecular spectra retrieved provide state-of-the-art results in line-center determination, achieving the same precision as currently available molecular databases. The devised setup provides a solid platform for a new generation of THz spectrometers, paving the way to more refined and sophisticated systems exploiting full phase control of QCL-FCs, or Doppler-free spectroscopic schemes.
关键词： frequency comb,spectroscopy,Quantum cascade laser,metrology,terahertz
更新于2025-09-23 15:21:01
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Temperature evolution in a pulsed CO<sub>2</sub>-N<sub>2</sub> glow discharge measured using quantum cascade laser absorption spectroscopy
摘要： This work uses in situ narrowband Quantum Cascade Laser (QCL) absorption spectroscopy to study the effect of N2 on the time evolution of gas temperature, rotational temperature and the vibrational temperatures of CO2 and CO in a pulsed glow discharge. Three colinear QCLs are used to scan three regions of about 1 cm?1 between 2179.20 and 2253.51 cm?1, including (v1, vl2 2 , v3 + 1) → (v1, vl2 2 , v3) CO2 transitions up to the asymmetric stretch level v3 = 6, as well as (vCO) → (vCO +1) CO transitions up to vCO = 1. A fitting routine is used to extract temperatures from the measured absorption spectra. The time resolved measurements are performed in CO2, admixed with up to 90% N2, with the plasma operated with a 5-10 ms on-off cycle, a discharge current of 50 mA and a pressure of around 6.7 mbar. The time evolution of the gas temperature has been measured and agrees well with the time evolution of the rotational temperature. The asymmetric stretch vibrational temperature T3 of CO2 reaches a maximum of 1060 K at 0.7 ms for pure CO2, while T3 goes up to 2250 K for a N2 content of 90% and stays constant until the plasma is switched off. Both T3 and the vibrational temperature of CO TCO show a clear non-equilibrium with respect to the rotational temperature Trot. Both do not equilibrate with the rotational temperature Trot between consecutive plasma cycles for a N2 content above 70%, although T3 and TCO always equilibrate with each other in the afterglow. The symmetric stretch and bending mode temperature T12 is elevated more with respect to the rotational temperature for increasing N2 content, while the maximum of the rotational temperature decreases for increasing N2 admixtures, which might be attributed to the energy stored in the vibrational modes of N2, CO2 and CO. Additionally, an indication of an increase in the total pressure during the plasma on-time due to heating and a subsequent decrease in the afterglow due to cooling was found for a pure CO2 plasma.
关键词： glow discharge,carbon dioxide plasma,vibrational temperature,gas temperature,quantum cascade laser
更新于2025-09-23 15:21:01
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Highly efficient surface-emitting semiconductor lasers exploiting quasi-crystalline distributed feedback photonic patterns
摘要： Quasi-crystal distributed feedback lasers do not require any form of mirror cavity to amplify and extract radiation. Once implemented on the top surface of a semiconductor laser, a quasi-crystal pattern can be used to tune both the radiation feedback and the extraction of highly radiative and high-quality-factor optical modes that do not have a defined symmetric or anti-symmetric nature. Therefore, this methodology offers the possibility to achieve efficient emission, combined with tailored spectra and controlled beam divergence. Here, we apply this concept to a one-dimensional quantum cascade wire laser. By lithographically patterning a series of air slits with different widths, following the Octonacci sequence, on the top metal layer of a double-metal quantum cascade laser operating at THz frequencies, we can vary the emission from single-frequency-mode to multimode over a 530-GHz bandwidth, achieving a maximum peak optical power of 240 mW (190 mW) in multimode (single-frequency-mode) lasers, with record slope efficiencies for multimode surface-emitting disordered THz lasers up to ≈570 mW/A at 78 K and ≈720 mW/A at 20 K and wall-plug efficiencies of η ≈ 1%.
关键词： quantum cascade laser,surface-emitting,Quasi-crystal,THz frequencies,Octonacci sequence,semiconductor lasers,distributed feedback
更新于2025-09-23 15:21:01
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High-resolution cw-cavity ring-down spectroscopy of allowed (??4??+????5)0 and forbidden (??4??+????5)2 bands of C2H2 using external-cavity quantum cascade laser
摘要： In this paper, we measured the absolute line intensities and air broadening coefficients of several rotationally resolved lines in the P and R branches of the allowed (ν4+ν5)0 and forbidden (ν4+ν5)2 vibrational combinational bands of C2H2 at room temperature 296K. These measurements were performed using an external-cavity quantum cascade laser (EC-QCL) operating at 7.5 μm coupled with high-sensitive cavity ring-down spectroscopy (CRDS). Rotational level-dependent pressure-broadening coefficients of the resolved spectral lines of the selected transitions from (ν4+ν5)0 band are reported here. The air broadening coefficients for 5 rotational lines from P-branch of (ν4+ν5)2 band were also obtained first time with better than 3% uncertainty. The vibrational transition dipole moment squared values of the rotational lines and empirical Herman-Wallis coefficients were also quantified from experimental data. Finally, experimentally obtained all spectroscopic parameters were rigorously compared with previous studies. The new experimental data including several spectroscopic parameters will be useful for atmospheric and astrophysics applications.
关键词： Cavity ring-down spectroscopy,Absolute measurement of line intensities and air broadening coefficients,Transition dipole moment,Ro-vibrational allowed and forbidden transition,Quantum cascade laser,Infrared spectra of Acetylene
更新于2025-09-23 15:21:01
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3.5 THz quantum-cascade laser emission from dual diagonal feedhorns
摘要： Antenna-pattern measurements obtained from a double-metal supra-terahertz-frequency (supra-THz) quantum cascade laser (QCL) are presented. The QCL is mounted within a mechanically micro-machined waveguide cavity containing dual diagonal feedhorns. Operating in continuous-wave mode at 3.5 THz, and at an ambient temperature of ～60 K, QCL emission has been directed via the feedhorns to a supra-THz detector mounted on a multi-axis linear scanner. Comparison of simulated and measured far-field antenna patterns shows an excellent degree of correlation between beamwidth (full-width-half-maximum) and sidelobe content and a very substantial improvement when compared with unmounted devices. Additionally, a single output has been used to successfully illuminate and demonstrate an optical breadboard arrangement associated with a future supra-THz Earth observation space-borne payload. Our novel device has therefore provided a valuable demonstration of the effectiveness of supra-THz diagonal feedhorns and QCL devices for future space-borne ultra-high-frequency Earth-observing heterodyne radiometers.
关键词： Supra-terahertz,heterodyne,dual diagonal feedhorn,earth observation,quantum-cascade laser,radiometer
更新于2025-09-23 15:19:57
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[IEEE 2019 Workshop on Recent Advances in Photonics (WRAP) - Guwahati, India (2019.12.13-2019.12.14)] 2019 Workshop on Recent Advances in Photonics (WRAP) - Quantum cascade laser-based in situ measurement of atmospheric CO and CO <sub/>2</sub> in Gandhinagar using 1f and 2f wavelength modulation spectroscopy
摘要： We report the design, development and field deployment of a quantum cascade laser-based tunable diode laser spectroscopy (TDLS) system for high-sensitivity measurement of atmospheric CO and CO2. Two distributed-feedback quantum cascade lasers are used to interrogate the rotational-vibrational transitions of CO at 4594.99 nm and CO2 at 4319.30 nm. The mean mole fraction values for CO and CO2 for the measurements made at Gandhinagar from 19-25 July 2019 are 477 ppb and 486 ppm respectively. The detection limit of the system is 3 ppb CO and 45 ppb CO2 for integration time of 17 s and 69 s respectively.
关键词： air quality monitoring,greenhouse gas monitoring,quantum cascade laser,wavelength modulation spectroscopy
更新于2025-09-23 15:19:57
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A Quantum Cascade Laser-Based Multi-Gas Sensor for Ambient Air Monitoring
摘要： A quantum cascade laser-based sensor for ambient air monitoring is presented and five gases, affecting the air quality, can be quantified. The light sources are selected to measure CO, NO, NO2, N2O and SO2. The footprint of the measurement setup is designed to fit in two standard 19” rack (48 cm × 65 cm) with 4 height units (18 cm) whereas one is holding the optical components and the other one contains the electronics and data processing unit. The concentrations of the individual analytes are measured using 2f-Wavelength Modulation Spectroscopy (2f-WMS) and a commercially available multipass gas cell defines the optical path. In addition, CO can also be measured with a dispersion-based technique, which allows one to cover a wider concentration range than 2f-WMS. The performance of this prototype has been evaluated in the lab and detection limits in the range of 1ppbv have been achieved. Finally, the applicability of this prototype for ambient air monitoring is shown in a five-week measurement campaign in cooperation with the Municipal Department for Environmental Protection (MA 22) of Vienna, Austria.
关键词： heterodyne phase sensitive dispersion spectroscopy,ambient air,infrared,quantum cascade laser,wavelength modulation spectroscopy
更新于2025-09-23 15:19:57