Quantum Kinetics of Laser-Induced Electron Hole Plasmas in Nanowire Arrays

光与物质的相互作用是科学研究的一个基本课题，对许多现代技术至关重要。光电子学的整个研究领域都在关注于光与电子材料组件的量子相互作用的解释，并且越来越多地在原子和分子的尺度上。对于许多半导体来说，强激光可以激发电子，然后留下带相反电荷的阴影，即所谓的“空穴”。这些电子和空穴表现得像固体内部的等离子体（带电粒子气体）。即使在今天的超级计算机上，在三维空间中求解描述等离子体的复杂方程也可能是令人望而却步的。然而，量子线的厚度比人的头发丝还小1000多倍，它们使我们能够在仅局限于一维空间的电荷上测试量子等离子体模型。该项目旨在计算相互作用量子线中电子-空穴等离子体的演化，以及激发它们的光的演化。目标是在十亿分之一秒的百万分之一的时间尺度上提高对光产生等离子体的光学和传输特性的认识。这些知识对于理解光-物质相互作用，以及纳米光电子学、传感和许多国家安全应用的进步非常重要。该项目在为本科生提供参与前沿研究的机会，根据研究成果开发新的大学课程课程，以及进行公共宣传方面也具有重要的广泛影响。在技术方面，该项目的目标是改进量子线中光激发电子-空穴等离子体的超快动力学计算，以及入射到量子线阵列上的超短激光脉冲的散射。计算将把模拟光传播的伪谱时域（PSTD）技术与量子线中多体等离子体动力学的量子动力学半导体布洛赫方程相结合。该项目通过摒弃通常用于简化此类计算的几个常见假设，提高了我们对固体等离子体动力学的认识；包括单色激光场、准平衡状态下的电子空穴分布、介质中的空间均匀电场，忽略了由空间电子空穴等离子体分布引起的纵向场。这些假设是当今涉及强光的光电计算的限制因素，特别是在纳米长度和飞秒时间尺度上。该项目将寻求找到量子线等离子体的局部响应与散射光脉冲的时空特征和相位之间的相关性的实验可测量指标。它还将寻找来自驱动电子-空穴等离子体的电流之间的可测量的相关性，以及由于量子线中诱导的、持久的等离子体振荡而产生的局部纵向电磁场。该项目的结果对于飞秒电子学和阿秒物理学等新兴领域的进步也将非常重要。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The interaction of light with matter is a fundamental topic of scientific research and critical to many modern technologies. The entire research field of optoelectronics is concerned with explaining the quantum interaction of light with electronic material components, increasingly on the scale of atoms and molecules. For many semiconductors, intense laser light can excite electrons, which then leave oppositely-charged shadows behind, known as "holes". These electrons and holes behave as a plasma (a gas of charged particles) confined within the solid. Solving the complicated equations describing such plasmas in three-dimensional space can be prohibitive, even on today's supercomputers. Quantum-wires, however, have a thickness over 1000 times smaller than a human hair, and they allow us to test quantum plasma models on charges that are confined to only one dimension in space. This project aims to calculate the evolution of electron-hole plasmas in interacting quantum wires, as well as the evolution of the light that excites them. The goal is to improve knowledge of optical and transport properties of light-generated plasmas on time-scales of a millionth of a billionth of a second. This knowledge is important for understanding of light-matter interactions, as well as advancements in nano-optoelectronics, sensing, and many national security applications. This project also has significant broader impacts in providing undergraduate students a chance to participate in cutting-edge research, development of new college course curricula based on the research results, and enabling public outreach.On the technical side, the goal of this project is to develop improved calculations of the ultrafast dynamics of photo-excited electron-hole plasmas in quantum wires, as well as the scattering of ultrashort laser pulses incident on a quantum wire array. The computations will couple Pseudo-Spectral Time Domain (PSTD) techniques of modeling light propagation to quantum-kinetic Semiconductor Bloch equations for the many-body plasma dynamics in the quantum wires. This project advances our knowledge of plasma dynamics in solids by dispensing with several common assumptions often used to simplify such calculations; including monochromatic laser fields, electron-hole distributions in quasi-equilibrium, spatially uniform electric fields in the medium, and neglect of longitudinal fields resulting from the spatial electron-hole plasma distribution. These assumptions are a limiting factor on today's optoelectronic calculations involving intense light, particularly on the nanometer length and femtosecond time scales. The project will seek to find experimentally measurable indicators of the correlation between the localized response of quantum-wire plasmas and the spatial-temporal features and phases of the scattered light pulses. It will also look for a measurable correlation between the current from driven electron-hole plasmas, as well as localized longitudinal electromagnetic fields due to induced, long-lasting plasma oscillations in the quantum wires. The results of the project will also be important for advancements in the emerging fields of femtosecond electronics and attosecond physics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.