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Terahertz Spectroscopy of Gas Mixtures with Dual Quantum Cascade Laser Frequency Combs
摘要： Terahertz laser frequency combs based on quantum cascade lasers provide coherent, broadband, electrically pumped, THz radiation sources for use in future spectroscopic applications. Here, we explore the feasibility of such lasers in a dual-comb spectroscopy configuration for the detection of multiple molecular samples in the gas phase. The lasers span approximately 180 GHz of optical bandwidth, centered at 3.4 THz with sub-milliwatt total optical power. One of the main advantages of dual-comb spectroscopy is its high speed, which opens up the possibility for direct observations of chemical reaction dynamics in the terahertz spectral region. As a proof-of-concept, we recorded continuously evolving spectra from gas mixtures with 1 ms temporal resolution.
关键词： frequency comb,multi-species,Terahertz,real-time,dual-comb spectroscopy,quantum cascade laser
更新于2025-09-23 15:19:57
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Optical external efficiency of terahertz quantum cascade laser based on ??erenkov difference frequency generation
摘要： In this paper, we consider terahertz sources based on ?erenkov di?erence frequency generation in a dual-wavelength mid-infrared quantum cascade laser and calculate analytically the optical external e±ciency of the out-going terahertz wave. The mid-infrared pumps operate simultaneously and have a common upper level. For short cavity lengths and low terahertz losses in the substrate, we ˉnd that implementation of the ?erenkov emission scheme in terahertz di?erence frequency generation quantum cascade lasers improves the optical external e±ciency dramatically. The maximum value of the latter is close to 19%, but is only attainable if the laser exhibits negligible mid-infrared transmission losses.
关键词： phased matching,Terahertz quantum cascade laser,optical external e±ciency,?erenkov,di?erence frequency generation
更新于2025-09-23 15:19:57
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Photon-driven broadband emission and frequency comb RF injection locking in THz quantum cascade lasers
摘要： We present homogeneous quantum cascade lasers (QCLs) emitting around 3 THz which display bandwidths up to 950 GHz with a single stable beatnote. Devices are spontaneously operating in a harmonic comb state, and when in a dense mode regime they can be injection locked at the cavity roundtrip frequency with very small RF powers down to -55 dBm. When operated in the electrically unstable region of negative differential resistance, the device displays ultra-broadband operation exceeding 1.83 THz (?f /f = 50%) with high phase noise, exhibiting self-sustained, periodic voltage oscillations. The low CW threshold (115 A· cm?2) and broadband comb operation (?f /f = 25%) make these sources extremely appealing for on-chip frequency comb applications.
关键词： quantum cascade laser,terahertz,domain formation,injection locking,frequency comb
更新于2025-09-23 15:19:57
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[IEEE ESSCIRC 2019 - IEEE 45th European Solid State Circuits Conference (ESSCIRC) - Cracow, Poland (2019.9.23-2019.9.26)] ESSCIRC 2019 - IEEE 45th European Solid State Circuits Conference (ESSCIRC) - A Hybrid THz Imaging System With a 100-Pixel CMOS Imager and a 3.25a??3.50 THz Quantum Cascade Laser Frequency Comb
摘要： The terahertz frequency range beyond 3 THz has exciting potential to have a transformative impact in a wide range of applications, including chemical and biomedical sensing, spectroscopy, imaging, and short-distance wireless communication. While there have been significant advancements in silicon-based THz imagers in the frequency ranges below 1 THz, technological development beyond 3 THz has been impeded by the lack of solid-state sources in this frequency range. In addition, the design space beyond 3 THz opens up fundamentally new challenges across electronics and the electromagnetic interface. In this spectral range, the wavelength is small enough (λox ≈ 50 μm at 3 THz) that a vertical via from the top antenna layer to the detector is a distributed element (transmission line or radiator). In this letter, we follow a careful circuits-electromagnetics co-design approach toward a hybrid imaging system with a 100-pixel CMOS imager that interfaces with a THz quantum cascade laser frequency comb that spans 3.25–3.5 THz with mode spacing of 17 GHz. The array chip, while designed for an optimal operation across 2.7–2.9 THz, demonstrates an average noise equivalent power (NEP) (across pixels) of 1260 pW/√Hz between 3.25–3.5 THz and a projected NEP of 284 pW/√Hz across the design range of 2.7–2.9 THz. To the best of our knowledge, we demonstrate for the first time full THz imaging in a hybrid quantum cascade laser (QCL)–CMOS fashion. This approach allows future works to leverage both QCL and CMOS technologies to demonstrate new technological advances for systems in the 1–10 THz range.
关键词： quantum cascade laser,THz imaging,terahertz,detector,imaging,CMOS,silicon,hybrid imaging
更新于2025-09-23 15:19:57
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Optimization of self-consistent approach for quantum cascade laser using shooting method and particle swarm optimization
摘要： We present a numerical optimization approach to simulate the output characteristics of a mid-infrared quantum cascade laser, taking into account the effect of subband electron temperature (Tei). The shooting method is used to simplify the calculation. The results give accurate subband electron temperatures when the external electric field is above the threshold. The results of the calculations are consistent with experimental results, thereby confirming that consideration of the subband electron temperature can improve our understanding of quantum cascade lasers and help guide future experimental work.
关键词： electron temperature,quantum cascade laser,infrared,shooting method
更新于2025-09-23 15:19:57
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Optical polarization shift in beams emitted by quantum cascade lasers
摘要： In this paper, we present experimental results of current-induced polarization change and transverse mode change in mid-infrared quantum cascade lasers. The polarization of laser beam was determined by measuring of far-field distributions of polarization projection on the linear polarization basis. The measured amount of TE-polarized light is associated with transversal mode structure, which was determined based on the far-field power distributions. The TE polarized light contribution in the beams varies from 6 to 19%. This quantity is anti-correlated to the fundamental transverse mode contribution.
关键词： Transverse modes,Quantum cascade laser,Broad-area lasers,Laser beam,Polarimetry
更新于2025-09-19 17:13:59
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A Sensitive Carbon Dioxide Sensor Based on Photoacoustic Spectroscopy with a Fixed Wavelength Quantum Cascade Laser
摘要： A photoacoustic spectroscopy (PAS) based carbon dioxide (CO2) sensor with a fixed wavelength quantum cascade laser (FW-QCL) was demonstrated. The emission wavelength of the FW-QCL at 4.42 μm in the mid-infrared spectral region matched a fundamental CO2 absorption line. Amplitude modulation of the laser intensity was used to match the resonant photoacoustic (PA) cell. The noise from the background was reduced with the correlation demodulation technique. The experimental results showed that the sensor had excellent signal stability and a concentration linear response. When the integration time was 1 s, a 1σ minimum detection limit (MDL) of 2.84 parts per million (ppm) for CO2 detection was achieved. The long-term stability of the sensor was evaluated by means of an Allan deviation analysis. With an integration time of ~100 s, the MDL was improved to 1 ppm. This sensor was also used to measure the CO2 concentration from some common emission sources, such as cigarette smoking, automobile exhaust, and the combustion of some carbon-containing materials, which confirmed the stability and robustness of the reported FW-QCL based CO2-PAS sensor system.
关键词： carbon dioxide detection,photoacoustic spectroscopy,quantum cascade laser
更新于2025-09-19 17:13:59
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Quantum cascade laser based, fiber coupled demultiplexed mid-infrared local oscillator for cryogenic applications
摘要： We have developed a fiber coupled demultiplexed local oscillator (LO) source for cryogenic applications based on a distributed feedback quantum cascade laser (QCL) at an operating wavelength of 10.6 μm. The coupling scheme relies on the combination of a phase grating generating multiple LO beams and a polycrystalline fiber delivering the demultiplexed LO signal to a superconducting mixer at 4 K in a closed-cycle cryostat. This scheme eases the use of a beam splitter in front of the mixer. Reflection phase grating generating 2 × 2 beams has been achieved with a total power efficiency of 64% based on a gold covered etched silicon nanostructure. The diffraction beam has been readily coupled into a 2 m long polycrystalline fiber, where a single-lobe circular beam has been delivered at the fiber output. By aligning the fiber core position to the center of a superconducting hot electron bolometer mixer at the rear side, we demonstrate the application of a fiber coupled demultiplexed QCL source for pumping the superconducting mixer with adequate LO power.
关键词： cryogenic applications,fiber coupled,local oscillator,quantum cascade laser,mid-infrared
更新于2025-09-19 17:13:59
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Noninvasive blood glucose detection by Quantum Cascade Laser
摘要： Quantum Cascade Laser (QCL) was invented in late 90s as a promising mid-infrared light source and contributed to the field of industry, military, medicine, and biology. The room temperature operation, watt-level output power, compact size, and wide tuning capability of this laser advanced the field of noninvasive blood glucose detection by exploring transmission, absorption, and photoacoustic spectroscopy. This review provides a complete overview of the recent progress and technical details of these spectroscopy techniques, using QCL as an infrared light source for detecting blood glucose concentration for diabetic patients.
关键词： transmission spectroscopy,Quantum Cascade Laser,mid-infrared,noninvasive blood glucose detection,photoacoustic spectroscopy,absorption spectroscopy
更新于2025-09-19 17:13:59
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High-Performance GaAs/AlAs Terahertz Quantum-Cascade Lasers For Spectroscopic Applications
摘要： We have developed terahertz (THz) quantum-cascade lasers (QCLs) based on GaAs/AlAs heterostructures for application-defined emission frequencies between 3.4 and 5.0 THz. Due to their narrow line width and rather large intrinsic tuning range, these THz QCLs can be used as local oscillators in airborne or satellite-based astronomical instruments or as radiation sources for high-resolution absorption spectroscopy, which is expected to allow for a quantitative determination of the density of atoms and ions in plasma processes. The GaAs/AlAs THz QCLs can be operated in mechanical cryocoolers and even in miniature cryocoolers due to the comparatively high wall-plug efficiency of around 0.2% and typical current densities below 500 A/cm2. These lasers emit output powers of more than 1 mW at operating temperatures up to about 70 K, which is sufficient for most of the abovementioned applications.
关键词： terahertz (THz) spectroscopy,Quantum-cascade laser (QCLs)
更新于2025-09-19 17:13:59