基于冷原子增益系统的光前驱波的实验研究

项目名称： 基于冷原子增益系统的光前驱波的实验研究

项目编号： No.11204235

项目类型： 青年科学基金项目

立项/批准年度： 2013

项目学科： 物理学I

项目作者： 卫栋

作者单位： 西安交通大学

项目金额： 30万元

中文摘要： 脉冲信号在色散介质中的传输是经典电磁学中的一个基本问题。当光脉冲信号在原子系统中传输时，脉冲的群速度可以大于或小于真空中的光速，但是信息的速度能否大于光速，是否会违反因果律？1914年，索末菲与布里渊指出一个阶跃脉冲信号的上升沿在色散介质中总是以真空中的光速传播，主信号则以群速度传播。这个上升沿是一种瞬态效应，叫做光前驱波。光前驱波与主信号混合在一起，在实验上很难将它们剥离开来。最近，在高光学厚度的冷原子系统中，利用EIT和慢光效应，我们成功地将光前驱波与延迟的主信号进行了分离。现在有许多工作研究光前驱波的特性，但是主要集中在吸收介质中并利用了EIT效应。本项目我们基于冷原子介质，在主动拉曼增益三能级与四能级系统中，在四波混频系统中研究光前驱波和透射脉冲的特性。通过改变介质厚度，探测光失谐量，输入脉冲形状，脉冲上升沿时间等参数来研究光前驱波的变化规律，深刻理解光前驱波的物理本质

中文关键词： 电磁感应透明；四波混频；光前驱波；艾里光束；拉盖尔高斯光束

英文摘要： Pulse propagation through a dispersive medium is a fundamental problem in classical electromagnetism. It is now possible to achieve slow or fast group velocity compared with the speed of light in vacuum c for pulses of light propagating through a gas of atoms. This triggered fundamental questions about the information velocity as it relates to causality in Einstein's special theory of relativity. In 1914, Sommerfeld and Brillouin showed theoretically that the front of a step-modulated optical pulse propagating in dispersive media always travels at the light velocity in vacuum c. This front, in the form of a transient wave now known as the optical precursor, is then followed by the main pulse traveling at its group velocity. In general, precursor signals are always mixed with main pulses. It is difficult to separate the optical precursors from the main pulse. Most recently, making use of electromagnetically induced transparency (EIT) and the slow-light effect in cold atoms with high optical depth, we successfully generated and separated the optical precursor from a delayed main field. Although many works have investigated the characteristics of optical precursors, most of them are based on EIT in atomic systems and consider an absorptive media. In this work we explore some characteristics of optical precursors a

英文关键词： electromagnetically induced transparency；four-wave mixing；optical precursors；Airy beams；Laguerre-Gaussian beams