【作者】 解研；

【导师】 赵宪庚； 段素青； 楚卫东；

【作者基本信息】 中国工程物理研究院 ， 理论物理， 2010， 博士

【摘要】 本论文重点研究了外加光场作用下半导体量子点结构中的光学特性,包括光吸收特性,量子干涉效应和强场中的非线性光学效应,并利用量子点结构的输运特性表征弱光场与体系相互作用产生的微弱光学信号。第一部分研究了耦合三量子点和量子环对弱光场的响应。首先,系统地研究了强驱动下耦合三量子点体系的量子干涉现象。借助光子辅助隧穿输运,将耦合三量子点对光场的响应呈现在体系的隧穿电流上,为实验在固体环境中获取光强较弱的相干光谱提供了一个可行的方案。通过调控耦合三量子点的能级结构,在吸收谱中相继观察到了由量子干涉效应带来的Autler-Townes劈裂、Mollow劈裂、无粒子数反转增益效应、相干俘获等量子相干特性,同时实现了对这些量子相干特性的调控。研究中考虑了声子的自发辐射对各能级电子布居数的影响。探讨了声子的辅助隧穿输运特性,其提供的背景电流可以用来判断驱动场对三能级结构的耦合状况。其次,研究了磁场调控下的量子环对太赫兹光的吸收特性。借助磁场对量子环能级的调制作用以及光子参与隧穿输运特性,提出了一种频率可调的太赫兹光探测理论模型。在此模型中,连续变化的外磁场实现了对太赫兹光探测的连续可调性；通过调控量子环的半径和宽度可以改变太赫兹光探测的频率范围。第二部分研究了量子点和耦合三量子点体系在强光场驱动下的高次谐波辐射特性。本论文研究了强微波场驱动下量子点体系的高次谐波辐射特性,提出了利用此非线性光学效应产生太赫兹辐射的设想。从量子输运动力学角度,揭示了输运体系准能带宽对高次谐波辐射效率起到的决定性作用。本论文进一步研究了强微波场驱动下的耦合三量子点三能级结构的高次谐波辐射机制和谐波辐射的偏振特性。发现在反演对称性缺失的多能级体系中,可以产生奇次、偶次谐波共存的高次谐波辐射,并阐明这种辐射特性的动力学机制。在耦合三量子点谐波辐射偏振特性的初步研究中,发现谐波辐射场中既有线偏振光又有椭圆偏振光,高次谐波辐射的偏振特性依赖于谐波阶次,并指出这些现象与耦合三量子点中各个偶极子的空间分布有着密切的联系。更多还原

【Abstract】 In this dissertation, we mainly focus on a theoretical study of the optical prop-erties of semiconductor quantum dot structures, including optical absorption prop-erties, quantum interference effects and nonlinear optical effects induced by intense fields. In particular, we use the transport properties of the quantum dot structures to obtain the optical signals induced by weak fields.In the first part of the dissertation, the response of coupled quantum dots and quantum rings to weak optical fields are investigated.Firstly, we systematically study the interference phenomena of serially coupled triple quantum dots driven by a strong driving and a weak probe field. The probe absorption spectra are shown in the photon-assisted tunneling current, which pro-vides a feasible way to obtain weak coherent optical signals in a solid environment. By changing the configuration of the three-level coupled triple quantum dot, we can obtain and control various quantum coherent properties such as Autler-Townes splitting, Mollow triplet, gain effect without population inversion, and coherent pop-ulation trapping. We also find that the effect of spontaneous emission of phonons may lead to an obvious background current, which can be used to distinguish which transition is driven by the driving field in experiments.And then we investigate the magnetic-field-modulated terahertz absorption spectra of a real GaAs quantum ring. As the energy levels of the quantum ring are modulated by an external magnetic field, the photon-participated tunneling current is used to show the features of the terahertz spectra of the quantum ring. Our study provides a possible way to realize tunable detection of terahertz fields. In such a scheme, tuning is performed via the external magnetic field, and the resonant frequency bands are handled by controlling the radius and width of the quantum ring.In the second part of the dissertation, the features of high-order harmonic generation in quantum dots and coupled quantum dots are explored.We first study the high-order harmonic spectra of a quantum dots driven by an intense microwave field. We propose a way to obtain terahertz radiation by using these nonlinear optical effects. By mapping the optical processes to quantum transport processes, we find that the efficiency of high-order harmonic generation is determined by the bandwidth of the quasienergy spectrum.Finally, we explore the features of high-order harmonic generation in coupled triple quantum dots in intense microwave fields. We find that multi-level systems in coupled triple quantum dots can generate odd-even order harmonics. The dynamic mechanism of high-order harmonic generation in optical coupled multi-level system is investigated. In addition, we make an elementary study on the polarization of the radiation. Due to the spatial configuration of the coupled triple quantum dots, the harmonic emission can be either linearly or elliptically polarized when driven by linearly polarized fields, and the polarization properties are found to be strongly dependent on the harmonic order.更多还原