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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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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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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) - Sub-terahertz Quantum-cascade Laser Source based on Difference-frequency Generation
摘要： Authors report a sub-terahertz monolithic semiconductor source based on a high power, long-wavelength quantum cascade laser. In order to obtain higher nonlinear susceptibility in the sub-terahertz frequency region, we design long wavelength dual-upper-state active region in which transition dipole moments are substantially increased. A fabricated device with distributed feedback grating produces nearly watt-level infrared output power, and as a result, it exhibits a peak output power of 18.5 μW at room temperature, around a frequency of ~700 GHz. Besides, the device produces an output power of 103 μW at 110 K.
关键词： dual-upper-state active region,monolithic semiconductor source,difference-frequency generation,sub-terahertz,quantum-cascade laser
更新于2025-09-16 10:30:52