Papers by Keyword: Quantum Cascade Laser

Abstract: This paper represents the line parameter measuring results base on pulsed DFB quantum cascade laser with tunable in the spectral range of 1248-1257 cm^-1. The transition is in the υ4 band and P (8) branch which is lying in the line position of 1253.46436 cm^-1 based on HITRAN simulation. The calculated line intensity is 1.85×1020 cm^-1/cm^-2molecule and the pressure broadening parameters in N₂ and Ar are 0.061± 0.003 cm^-1atm^-1 and 0.086 ± 0.007 cm^-1atm^-1 respectively.

Abstract: Based on the dynamic analysis and numerical computation of quantum cascade laser(QCL), a simple equivalent circuit model of QCL was established, in which we considered the spontaneous emission effect for QCL's start delay. The direct current(DC), transient and frequency response characteristics of QCL were obtained by means of the circuit simulation of PSPICE program, and some relevant parameters that may affect the QCL performance have been analyzed. The results of simulation are consistent with that of numerical calculation in previous literatures.

Abstract: This paper presents a novel valance intersubband laser based on Si-based Si-Ge superlattices grown on a relaxed Si0.5Ge0.5 buffer layer. Effective mass theory is used to calculate the inplane valence subband dispersion of Si-Ge superlattices within 6×6 Kane model. Analysis of the inplane energy dispersion shows that the light-hole effective mass is inverted at off zone center region. The laser structure can be designed with a simple quantum cascade scheme. Our calculation shows that with the electrical pump, it is possible to achieve population inversion between the two subbands at local k space where the light-hole effective mass is inverted. Optical gain of the order 100/cm can be achieved with a pumping current density 10 kA/cm2.

Abstract: An experimental and theoretical comparative analysis of the output characteristics of λ ≈ 9m GaAs/Al0.45Ga0.55As quantum cascade lasers based on single and double phonon resonance depopulation mechanisms were presented. The layer structures were grown with solid source molecular beam epitaxy and consist of 48 or 36 active stages embedded in a symmetrical plasmon enhanced waveguide. From the wafers, ridge waveguide lasers were fabricated by optical lithography and dry etching. The theoretical model is based on a fully non-equilibrium Schrödinger- Poisson self-consistent analysis of the coupled scattering rate and single-temperature energy balance equations, taking all relevant electron-LO phonon, electron-electron and electron-ionised impurity scattering processes into account. Single phonon resonance devices exhibit clear current saturation, simultaneously with a decrease of the optical power. In the moderate doping regime, a quasi-linear dependence of both the threshold and saturation current densities on injector doping, were measured, in a very good agreement with theoretical predictions. Double phonon resonance lasers exhibit ‘saturation’ mechanism evident from their decrease in optical power, but without pronounced current saturation. Previously reported saturation of the ‘maximal’ current under higher injector doping in single phonon resonance lasers, is also observed in the double phonon resonance structure for injector sheet doping above 8x1011cm-2.

Abstract: The optical gain in the active region of quantum cascade laser in an external magnetic field is analyzed. When the magnetic field is applied in the direction perpendicular to the plane of the layers, electron dispersion is broken into series of discrete Landau levels. This additional confinement strongly modifies the lifetime of electrons in the upper state of the laser transition, which is controlled by electron-phonon scattering. Landau levels are magnetically tuneable and, depending on their configuration, phonon emission is either inhibited or resonantly enhanced. This translates into a strong modulation of the population inversion, and consequently of the optical gain by varying the magnetic field. Numerical results are presented for a structure previously considered by Smirnov et al. [Phys. Rev B 66 (2002) 125317] which is designed to emit radiation at λ~11.4µm, with the magnetic field varied in the range 10-60T. The effects of band nonparabolicity are taken into account in this model.

Abstract: In this paper a procedure for the global optimization of mid-infrared GaAs/AlGaAs quantum cascade lasers that relies on the method of simulated annealing is presented. We propose a double longitudinal optical phonon resonance design obtained via a ladder of three states, with subsequent pairs separated by optical phonon energy. Addition of an extra level decreases the lower laser level population by enabling an efficient extraction into the injector region. The output characteristics of the optimized structures are calculated using the full self–consistent rate equation model, which includes all of the relevant scattering mechanisms. We also presented the experimentally measured output characteristics of an initial device, which are in agreement with the numerically calculated values, confirming the good design capabilities of the applied procedure.

Abstract: Asymmetric rolling, in which the circumferential velocities of the upper and lower rolls are different, can give rise to intense plastic shear strains and in turn shear deformation textures through the sheet thickness. The ideal shear deformation texture of fcc metals can be approximated by the <111> // ND and {001}<110> orientations, among which the former improves the deep drawability. The ideal shear deformation texture for bcc metals can be approximated by the Goss {110}<001> and {112}<111> orientations, among which the former improves the magnetic permeability along the <100> directions and is the prime orientation in grain oriented silicon steels. The intense shear strains can result in the grain refinement and hence improve echanical properties. Steel sheets, especially ferritic stainless steel sheets, and luminum alloy sheets may exhibit an undesirable surface roughening known as ridging or roping, when elongated along RD and TD, respectively. The ridging or roping is caused by differently oriented colonies, which are resulted from the <100> oriented columnar structure in ingots or billets, especially for ferritic stainless steels, that is not easily destroyed by the conventional rolling. The breakdown of columnar structure and the grain refinement can be achieved by asymmetric rolling, resulting in a decrease in the ridging problem.