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Theoretical Research of Optical Pulse Response of Quantum Confined Excitons

量子约束激子光脉冲响应的理论研究

基本信息

批准号：
09640396
负责人：
ISHIHARA Hajime
金额：
$ 2.05万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1999
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09640396/
关键词：
Nonlinear Optics Optical Pulse Excitons Polaritons Ultra fast response Mesoscopic systems Nano-scale matters Thin film パルス応答

项目摘要

We have developed the theory for the optical response of the ultra short pulse in which the nanoscale spatial structure of the response field in the media is correctly considered. This theory has following features.The nonlocal response is considered.The microscopic position dependences of the induced current density and the response field are correctly taken into account.The self-consistency of the induced current density and the response field are taken into account.Nonlinear response can be treated.We take the method such that the simultaneous equations of Maxwell eq. and the equation for the density matrix of the matter system are numerically solved. Taking the rotating wave approximation and slowly varing envelope approximation in time, and reducing the number of the exctitonic states as bases, we make this calculation feasible. Appling this method to the ultra thin film confining excitons, we have clarified the following points.1.The remarkable nanoscale spatial structure of the response field appears even for the short pulse of several hundreds femto second, and the selection rule that should hold in the case of long wavelength is broken for both the linear and nonlinear regimes. We understand that our approach is essentially necessary in such conditions.2.We elucidate, for the first time, the real time characteristics of the internal field by the short pulse undergoing multiple reflection.3.The time characteristics of the nonlinear signal reflects the above mentioned motion of the internal field in time, thus, the nano-scale spatial structure of the internal field takes a important role in the time characteristics of the nonlinear response. It is also clarified that if we neglect this spatial structure of the internal field, we can not describe the correct time variation of the nonlinear signal at all.

我们正确考虑了介质中响应场的纳米尺度空间结构，发展了超短脉冲的光学响应理论。该理论具有如下特点：考虑了非局域响应；正确地考虑了感应电流密度和响应场的微观位置相关性；考虑了感应电流密度和响应场的自洽；可以处理非线性响应。对物质系统的密度矩阵方程进行了数值求解。以旋波近似和随时间缓慢变化的包络近似为基础，以减少激子态数为基础，使计算变得可行。将这种方法应用于超薄膜禁闭激子，我们澄清了以下几点：1.即使在几百飞秒的短脉冲下，响应场也出现了显著的纳米级空间结构，并且打破了线性和非线性区域在长波长情况下应该适用的选择规则。在这种情况下，我们的方法是必要的。2.首次阐明了短脉冲多次反射内场的实时特性。3.非线性信号的时间特性反映了上述内场在时间上的运动，因此，内场的纳米尺度空间结构对非线性响应的时间特性具有重要作用。如果忽略内场的这种空间结构，我们根本不能描述非线性信号的正确时变。