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Terahertz Computed Tomorgraphy with a Quantum Cascade Laser and a Quantum-well Photodetector
Tao Zhou,Li Gu,Zhi-Yong Tan,Jun Cheng Cao 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.2
In this letter, a terahertz (THz) tomography system based on a quantum cascade laser (QCL)and a quantum-well photodetector (QWP) is demonstrated. The QCL provides a relatively high power (a few microwatts) in a continuous-wave mode at 3.9 THz as a light source, and the QWP provides a narrow response range from 3 to 7 THz with a calibrated peak response of 0.5 A/W under background-limited performance. We employ the widely-used filtered back projection (FBP)and algebraic reconstruction algorithms for terahertz tomography technology. The reconstructed cross-sectional image of a sample has successfully revealed the internal and the external structures with a resolution of around 1.5 mm. This experiment demonstrates that the terahertz QCL and the photodetector are potentially useful for terahertz tomography applications.
Yousefvand Hossein Reza 한국물리학회 2022 Current Applied Physics Vol.39 No.-
In this paper, a quantum cascade laser (QCL) design is proposed based on GaAs/AlGaAs material system, which simultaneously operates at three widely separated wavelengths (λ1 = 11.1 μm, λ2 = 14.1 μm and λTHz = 60 μm). In the design, all the wavelength radiations are achieved by the engineering of the electronic spectrum via the quantum-well widths and the applied electric field in a single active region within a same waveguide. The midinfrared (mid-IR) wavelengths are obtained by adoption a dual-upper-state active region, and the proposed design aims to use both the mid-IR radiations as the coherent deriving fields to populate the upper THz lasing state to aid the THz-laser population inversion via optical pumping instead of direct electrical injection. A detailed analysis of electronic transport in the structure is carried out using a multi-level rate-equation model. The results show that the proposed structure offers an alternative approach to room temperature THz generation in QCLs.
Spectral Research on an AlGaAs Epitaxial Material for a Terahertz Quantum-cascade Laser
Zhi-Yong Tan,Jun-Cheng Cao 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.8
The spectral properties of a series of AlGaAs epitaxial films were studied by using a Fourier transform infrared spectrometer with an 80-degree grazing incidence reflection unit. The AlAslike transversal optical phonon was obviously observed in the spectra, but the longitudinal optical phonon was obscured in the transmission spectra. The variation curves for the transversal optical phonon energy were acquired from the two kinds of spectra and were compared with each other and with the early results. A comparison of the results show that the grazing incidence reflection spectrum is better in reflecting the AlAs-like phonon energy of an AlGaAs epitaxial film and could be a supplementary means in the characterization of the material for a terahertz quantum-cascade laser.
Dephasing Effect on the Carrier-light Interaction in Terahertz Quantum Cascade Lasers
Feng Wang,Xu Guang Guo,Jun Cheng Cao 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.41
We study the dephasing effect on the carrier-light interaction in terahertz quantum cascade lasers by using a rate-equation method including the optical field. The time evolution of the gain coefficient and the stimulated radiation rate are shown. We theoretically provide an ultrafast microscopic process for the conversion of a working terahertz quantum cascade laser from an unsaturated to a saturated state.
고영환,박범두,유재수 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.9
We designed and analyzed the semi-insulating surface plasmon waveguide structures of GaSb-based quantum cascade lasers (QCLs) operating in the terahertz (THz) region of 2.6-6.5 THz using the finite element method. In order to improve the guiding property of THz QCL waveguide structures, the low threshold gain (gth) and high optical confinement (Γ) could be achieved by optimizing the doping concentration and thickness of plasma layer, waveguide width, thickness of substrate, and number of stages in the active region at various operating frequencies (2.6 - 6.5 THz). The effect of different substrates on the gth and Γ of THz QCL waveguide structures was also investigated.