Multi-Watt high-power terahertz (THz) frequency quantum cascade lasers are demonstrated, based on a single, epitaxially grown, 24-μm-thick active region embedded into a surface-plasmon waveguide. The devices emit in pulsed mode at a frequency of ∼4.4 THz and have a maximum operating temperature of 132 K. The maximum measurable emitted powers from a single facet are ∼2.4 W at 10 K and ∼1.8 W at 77 K, with no correction being made for the optical collection efficiency of the apparatus, or absorption by the cryostat polyethylene window.Introduction: Terahertz (THz) frequency radiation has many potential applications, ranging from imaging, bio-and chemical-sensing, and non-destructive testing, through to security scanning, industrial process monitoring, and telecommunications [1,2]. However, one of the principal challenges is to develop compact, low-cost, efficient THz sources. In this respect, the development of the THz quantum cascade laser (QCL) provides a potential solid-state solution [3]. Nevertheless, for many remote sensing and imaging applications, for example, realtime measurement using a THz camera, high optical powers are desirable [4]. In addition, a high-power THz source is attractive for the investigation of non-linear physics at THz frequencies.In general, increased output powers can be obtained, in both conventional interband semiconductor lasers and mid-infrared QCLs, by using broader area cavities [5]. Relying on this strategy, we previously demonstrated 1.01 W peak output powers (P peak ) from a broad-area THz QCL [6]. However, scaling the device area to an even larger value leads to difficulties in managing the significant Joule heating and random filamentation [5]. As an alternative, the power can be increased by increasing the active region thickness, i.e. the number of cascade periods [7]. Indeed, THz QCLs with P peak of up to 470 mW per facet at 5 K have been demonstrated, using a direct wafer-bonding technique to stack two separate 10-μm-thick THz QCLs together, thereby increasing the active region thickness [8]. This approach, however, requires the QCL to have a symmetric active region, limiting widespread applicability of the technique. In this Letter, we demonstrate multi-Watt high-power THz QCLs with a 24-μm-thick active region, grown in a single epitaxial growth. The devices operate in pulsed mode with emission at a frequency of ∼4.4 THz and deliver P peak up to ∼2.4 W at 10 K and ∼1.8 W at 77 K.
The authors demonstrate a broadband, heterogeneous terahertz frequency quantum cascade laser by exploiting an active region design based on longitudinal optical-phonon-assisted interminiband transitions. They obtain continuous wave laser emission with a threshold current density of ∼120 A/cm 2 , a dynamic range of ∼3.1, and an emission spectrum spanning from 2.4 to 3.4 THz at 15 K.
Background: From a chemistry point of view, we hypothesized that superlative dual cytotoxicity-radical scavenging bioefficacies of series 4 FQs correlate to their acidic groups and C8-C7 ethylene diamine Chelation Bridge. Methodology: Newly synthesized 16 lipophilic-acid chelating FQs have been screened for in vitro duality of proliferation inhibition and radical scavenging capacities. Results: Substantially in LPS prompted RAW264.7 macrophages inflammation, IC50 values (µM) in the ascending order of new FQs' NO scavenging/antiinflammation capacity were 4e<4b<3d<4f<5c
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 highfrequency 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 tõ 800 ps by our measurement system, theoretical considerations suggest considerably faster modulation could be possible.
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