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Nonlinear Optics || The Nonlinear Optical Susceptibility
摘要： Nonlinear optics is the study of phenomena that occur as a consequence of the modification of the optical properties of a material system by the presence of light. Typically, only laser light is sufficiently intense to modify the optical properties of a material system in this manner. The beginning of the field of nonlinear optics is often taken to be the discovery of second-harmonic generation by Franken et al. (1961), shortly after the demonstration of the first working laser by Maiman in 1960. Nonlinear optical phenomena are "nonlinear" in the sense that they occur when the response of a material system to an applied optical field depends in a nonlinear manner on the strength of the applied optical field. For example, second-harmonic generation occurs as a result of the part of the atomic response that scales quadratically with the strength of the applied optical field. Consequently, the intensity of the light generated at the second-harmonic frequency tends to increase as the square of the intensity of the applied laser light.
关键词： Material system,Optical properties,Nonlinear optics,Laser light,Second-harmonic generation
更新于2025-09-23 15:21:01
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Nonlinear Optics || Spontaneous Light Scattering and Acoustooptics
摘要： In this chapter, we describe spontaneous light scattering; Chapters 9 and 10 present descriptions of various stimulated light-scattering processes. By spontaneous light scattering, we mean light scattering under conditions such that the optical properties of the material system are unmodified by the presence of the incident light beam. We shall see in the following two chapters that the character of the light-scattering process is profoundly modified whenever the intensity of the incident light is sufficiently large to modify the optical properties of the material system.
关键词： stimulated light-scattering,spontaneous light scattering,material system,optical properties,incident light
更新于2025-09-23 15:21:01
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Activated Auger Processes and their Wavelength Dependence in Type-I Mid-Infrared Laser Diodes
摘要： Type-I quantum well (QW) lasers based on the GaSb material system show attractive characteristics in the mid-infrared [1]. However, as the wavelength (λ) increases in the range of 2-4 μm their performance begins to deteriorate due to increasing Auger recombination [2]. In the Auger process, the energy released from an electron-hole recombination is transferred to a third carrier. In order to develop strategies to suppress Auger recombination, it is crucial to understand the magnitude and nature of the dominant Auger recombination pathway, and their dependencies on the operating λ and temperature (T). In QW structures two fundamentally different Auger process can occur [3]. In an activated Auger process, initial and final carrier states are confined to the plane of the QW. The recombination rate due to this process depends exponentially on T because it is determined by an activation energy, which is a consequence of energy and momentum conservation. In a thresholdless Auger process, the initial carrier states can exist near the band edge (bottom of conduction/valence band) and the third carrier is excited into the continuum of unbound states in a direction perpendicular to the plane of the well. Without an activation energy, the thresholdless Auger process exhibits only a weak T dependence. In this work, we report on the T and λ dependence of the threshold current density (Jth) of type-I QW devices operating in range 1.95-3.2 μm. From T-dependent measurements, we find that radiative recombination dominates from low T up to a break point temperature [4]. Beyond this break point the temperature sensitivity of Jth increases rapidly, indicating the onset of a strongly temperature-sensitive activated Auger process. Using hydrostatic pressure, we tune the operating λ of the lasers in order to probe the λ dependence of the Auger coefficient. Modelling the gain and loss characteristics of the lasers allowed the threshold carrier density (nth) to be determined. Since the carrier density calculations depend sensitively on the threshold gain, we undertook segmented contact measurements to experimentally determine the optical loss. By extracting the experimentally-determined radiative component of Jth and assuming the remaining non-radiative current (cid:1836)(cid:1866)(cid:1870)=(cid:1829)(cid:1866)(cid:1872)?, C and its λ dependence were calculated, although the analysis also provides evidence that the dependence is not strictly cubic (i.e., C depends on nth).
关键词： temperature dependence,Type-I quantum well lasers,Auger recombination,mid-infrared,wavelength dependence,GaSb material system
更新于2025-09-12 10:27:22
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[IEEE 2018 IEEE Symposium on VLSI Technology - Honolulu, HI (2018.6.18-2018.6.22)] 2018 IEEE Symposium on VLSI Technology - Record 47 mV/dec top-down vertical nanowire InGaAs/GaAsSb tunnel FETs
摘要： Pocketed vertical nanowire InGaAs/GaAsSb tunnel FETs (TFET) with sub-threshold swing (SS) reaching 47 mV/dec are demonstrated. The achieved sub-threshold performance is the steepest reported so far for a top-down TFET in the III-V material system. Smooth vertical wires with diameters as narrow as 30 nm are achieved using a CH4 based dry etch process. Drive current at 0.35 V supply voltage approaches 0.7 μA/μm for a fixed Ioff of 1 nA/μm.
关键词： tunnel FETs,InGaAs/GaAsSb,vertical nanowire,sub-threshold swing,III-V material system
更新于2025-09-04 15:30:14