Optical Properties of Terahertz-Modulated Quantum Structures

太赫兹调制量子结构的光学特性

• 批准号: 0223770
• 负责人: David Citrin
• 金额: $ 20.35万
• 依托单位: Georgia Tech Research Corporation
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-08-16 至 2003-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0223770&HistoricalAwards=false
• 关键词: Optical; Properties; Terahertz; Modulated; Quantum

0073364CitrinThis research grant focuses on the optical properties of semiconductor heterostructures, including quantum wells (QW's), quantum wires (QWR's), quantum dots (QD's) and microcavities (MC's), in the presence of terahertz (THz) electromagnetic fields. This research area, in addition to being of fundamental interest, has received a two-fold impetus from high-speed electronics and from high-bandwidth optical communications. Of particular interest to this research is the regime of low carrier density in which few electrons or holes are excited by the optical beam; the coherence properties of the carriers play an essential role. Previous reseach considered the dynamics of electron-hole (e-h) pairs excited by ultrafast optical pulses in the presence of THz fields. Because the bandwidth of a sub-ps optical pulse can be in excess of 10 meV, e-h pairs with varying degrees of excess energy (or excitons in different states of their internal motion) are excited by the optical pulse forming a wavepacket. Such studies provide an analogy to several atomic physics phenomena, including the dynamics of Rydberg wavepackets, above-threshold ionization, and high-field harmonic generation. The focus of the proposed work is to explore this analogy further, but more so to push into the domain where intrinsic solid state effects, such as many-body effects and carrier-phonon scattering, begin to make their presence felt by leading to dephasing of the optically excited e-h pairs. Thus, the first optical nonlinearities that kick in as the optical intensity is increased beyond the linear optical regime will be studied. Specifically, how do carrier-carrier and carrier-phonon scattering lead to dephasing of the optically excited electronic excitations, and how does this dephasing modify the spatial motion of e-h wavepackets excited by short optical pulses and driven by THz fields? What is the nature of phonons emitted by such wavepackets; can coherent wavepackets of phonons be launched by THz-driven e-h wavepackets? Can scattering rates themselves be modified by the dynamics of the THz-driven e-h wavepackets?In addition to being an untapped area of fundamental importance in the spectroscopy of semiconductors, light propagation through THz-modulated quantum wells povides an optical analog for a class of time-domain single-particle quantum tranport phenomena that are otherwise infeasible to study. In particular, tracking the temporal evolution of coherent wavepackets during the tunneling process is of fundamental interest and yet difficult, if not in practice impossible, to access in quantum transport experiments. Fortuitously, there is a close analogy between the scalar classical electromagnetic wave equation and the single-particle Schroedinger equation. This means that in a certain regime one can model by correspondence the quantum mechanical dynamics of a particle by an appropriate light-propagation experiment. This correspondence extends to the phase, i.e., quantum mechanical phase maps to optical phase. Clearly, interferometric experiments are routine in optics but require a tour de force effort in quantum transport. A particularly interesting class of phenomena involves quantum tunneling through a time-modulated potential. The connections between the same type of processes that are associated with the formation of THz sidebands on optical spectra of THz illuminated semiconductors with quantum transport phenomena.The theoretical research will focus on regimes where neither the QW/atom or optical/transport analogies entirely hold, such as the nonlinear optical regime - where THz-modulated semiconductor heterostructures present new possibilities. Specifically, the propagation of cw and ultrafast optical pulses through heterostructures subjected to pulsed or narrow-band THz fields will be studied.%%% This research grant focuses on the optical properties of semiconductor heterostructures, including quantum wells (QW's), quantum wires (QWR's), quantum dots (QD's) and microcavities (MC's), in the presence of terahertz (THz) electromagnetic fields. This research area, in addition to being of fundamental interest, has received a two-fold impetus from high-speed electronics and from high-bandwidth optical communications. Of particular interest to this research is the regime of low carrier density in which few electrons or holes are excited by the optical beam; the coherence properties of the carriers play an essential role. ***

这项研究经费主要集中在半导体异质结构的光学性质，包括量子井(QW)、量子线(QWR)、量子点(QD)和微腔(MC)，在太赫兹(THz)电磁场存在的情况下。这一研究领域除了具有根本意义外，还受到高速电子学和高带宽光通信的双重推动。这项研究特别感兴趣的是低载流子密度的区域，在该区域中，很少有电子或空穴被光束激发；载流子的相干特性起着至关重要的作用。前人研究了太赫兹场中超快光脉冲激发的电子-空穴(e-h)对的动力学。因为亚ps光脉冲的带宽可以超过10 meV，所以具有不同程度过剩能量(或处于不同内部运动状态的激子)的e-h对被形成波包的光脉冲激发。这样的研究提供了对几种原子物理现象的类比，包括里德堡波包的动力学、高于阈值的电离和高场谐波产生。这项工作的重点是进一步探索这种类比，但更重要的是要深入到本征固态效应，如多体效应和载流子-声子散射，通过导致光学激发的e-h对的退相而开始感受到它们的存在的领域。因此，将研究当光强度增加到超过线性光学区域时所产生的第一个光学非线性。具体地说，载流子-载流子和载流子-声子散射如何导致光激发电子激发的退相，以及这种退相如何改变由短光脉冲激发和THz场驱动的e-h波包的空间运动？由这样的波包发出的声子的性质是什么？太赫兹驱动的e-h波包能发射相干的声子波包吗？散射率本身能被太赫兹驱动的e-h波包的动力学所改变吗？除了是半导体光谱学中一个尚未开发的重要领域，光通过太赫兹调制量子井的传播还为一类无法研究的时间域单粒子量子传输现象提供了光学类比。特别是，在隧道过程中跟踪相干波包的时间演化是基本感兴趣的，但在量子输运实验中很难获得，如果在实践中不是不可能的话。幸运的是，标量经典电磁波方程与单粒子薛定谔方程有着密切的相似之处。这意味着，在一定的范围内，人们可以通过适当的光传输实验，通过对应的方式来模拟粒子的量子力学动力学。这种对应关系延伸到位相，即量子力学相到光学相的映射。显然，干涉测量实验在光学领域是司空见惯的，但在量子传输方面需要付出巨大的努力。一类特别有趣的现象涉及通过时间调制势的量子隧穿。与在THz光谱上形成THz边带相关的相同类型的过程之间的联系用量子输运现象照亮了半导体。理论研究将集中在量子波/原子或光学/输运类比都不完全成立的区域，例如非线性光学区域--其中THz调制的半导体异质结提供了新的可能性。具体地说，将研究连续波和超快光脉冲在脉冲或窄带THz场作用下通过异质结构的传输。%本研究经费主要研究半导体异质结构在太赫兹(THz)电磁场存在下的光学性质，包括量子井(QW)、量子线(QWR)、量子点(QD)和微腔(MC)。这一研究领域除了具有根本意义外，还受到高速电子学和高带宽光通信的双重推动。这项研究特别感兴趣的是低载流子密度的区域，在该区域中，很少有电子或空穴被光束激发；载流子的相干特性起着至关重要的作用。***