电磁波在周期介质中的传播及二维光子晶体的光子带结构

光子晶体是光学与凝聚态物理交叉的新领域,也是近年来应用物理学的一个重要研究领域,它是一种由介电常数高的(低的)介质在另一种介电常数低的(高的)背景介质中周期排列所组成的人造多维周期结构材料,能够产生光子带隙。频率落在带隙内的光在晶体里沿任何方向都不能传播,因而具有能够抑制原子、分子的自发辐射等诱人的光电子学特性,在基础研究和实际应用上都有着巨大的潜力。本文在这一领域里进行了富有成效的研究,获得了很好的结果。主要有:(1)利用平面波展开方法来计算二维光子晶体的带隙结构。首先,我们设计正方晶胞的二维光子晶体模型。设x₃方向为介质柱的轴方向,二维周期结构在x₁-x₂平面上。晶胞的晶格常数为a,半径为r,介质柱和空气柱的介电常数分别为ε_a=17和ε_b=1,a>2r。设计的核心思想是通过降低光子晶体结构的对称性,消除光子能带在晶体的布里渊区高对称点上的本征简并。(2)对于二维光子晶体的电磁波理论及周期介质中的Bloch波解做了详细的推导,给出了光子晶体中禁带存在的理论依据。同时以正方格子晶格的二维光子晶体为例,验证了电介质在空气圆孔中的排列存在E偏振和H偏振的光子带隙重叠区,称为绝对光子带隙。对于二维的光子晶体,两种本征偏振模式的光子能带结构可以独立地调节,以实现两者的光子带隙的最优重叠, 从而大大提高了二维光子晶体的完全带隙宽度。     

光折变有机聚合物中的空间孤子

给出了稳态情况下光折变聚合物中光波演化方程的亮、暗及灰孤子解,并讨论了不同孤子态的偏振特性及孤子宽度与外加电场的关系. 关键词： 光折变 聚合物 空间孤子     

单壁碳纳米管能带及其电子特性研究

从能带理论出发,采用电子紧束缚能量色散关系,推导锯齿,扶手椅和手性单壁碳纳米管(SWCNT)的电子能带结构表达式,指出单壁碳纳米管或为金属或为半导体的判据。结果表示:单壁碳纳米管的电子结构与其几何结构密切相关,如扶手椅型单壁碳纳米管是金属性的,而对其它类型的单壁碳纳米管是与碳纳米管的手性指数有关,只有手性指数n和m的差别等于3的倍数时,单壁碳纳米管是金属性的,否则会显出有带隙的半导体特性。这意味着单壁碳纳米管是由特殊的电子传输和光学性质,在纳米电子学领域具有巨大的潜在应用价值。     

不确定度在物理实验中的应用

目前，新疆大学物理实验的数据处理中还未采用测量不确定度这一概记念，本文从不确定度的基本概念出发，介绍在物理实验中的实际应用。     

Manakov Soliton Pairs in Biased Photovoltaic Photorefractive Crystals

We study,theoretically,incoherently coupled screening-photovoltaic soliton pairs in biased photovoltaic photorefractive crystals.It is shown that when the total intensity of two coupled solitons is much lower than the effective dark irradiance,the coupled soliton equations reduce to the Manakov equations.The dark-dark,bright-bright and dark-bright soliton pair solutions of these Manakov equations are obtained under an appropriate external bias field and a photovoltaic field,and the characteristics of these Manakov soliton pairs are also discussed in detail.     

Energy levels and states of parabolic cylindrical lens shaped quantum dots

The parabolic cylindrical lens shaped quantum dot is investigated theoretically. The Schrǒdinger equation for an electron confined in this structure is solved in the parabolic cylindrical coordinate system. The wavefunctions for the electron are presented in terms of confluent hypergeometric functions, and the electron energy spectra are also obtained.     

天线结构设计中鱼骨形主力骨架自振频率计算

对雷达天线结构设计中鱼骨形主力骨架的自振频率进行了分析,给出了用能量法进行计算的方法,在数据处理中使用了未确知有理数的方法,结果更准确,误差更小。     

光子晶体空气孔中质量分数对其禁带宽度影响的仿真分析

为了掌握光子晶体空气孔中液体质量分数对禁带宽度的影响,利用平面波展开法研究了由椭圆形空气孔介质周期性排列的长方晶格光子晶体在不同偏振模式下的禁带宽度。数值模拟显示:溶液的质量分数变化与光子晶体带隙宽度或输出功率变化接近线性关系,而线性相关程度受填充空气孔内液体质量分数的影响。进行了多组参数比对与优化,最终获得了线性度最高的禁带宽度和输出功率与溶液质量分数的对应关系。基于这个对应关系,提出了基于光子晶体带隙宽度测量的溶液质量分数检测方法。该方法可被应用于各蛋白质聚集探测、快速检测气体或液体质量分数、DNA检测等领域。     

高能离子的定向发射及其模拟研究

本文用二维粒子模拟方法研究了超强超短脉冲激光与圆形等离子体薄靶相互作用中产生的高能离子.模拟研究结果表明,在圆形等离子体薄靶后表面所产生的高能离子,角分布较小,定向性好,能获得很高的能量,并且等离子体薄靶的形状对高能离子的产生和会聚有一定地影响.     

Ultrabright γ-ray emission from the interaction of an intense laser pulse with a near-critical-density plasma

An efficient scheme for generating ultrabright γ-rays from the interaction of an intense laser pulse with a near-critical-density plasma is studied by using the two-dimensional particle-in-cell simulation including quantum electrodynamic effects. We investigate the effects of target shape on γ-ray generation efficiency using three configurations of the solid foils attached behind the near-critical-density plasma: a flat foil without a channel (target 1), a flat foil with a channel (target 2), and a convex foil with a channel (target 3). When an intense laser propagates in a near-critical-density plasma, a large number of electrons are trapped and accelerated to GeV energy, and emit γ-rays via nonlinear betatron oscillation in the first stage. In the second stage, the accelerated electrons collide with the laser pulse reflected from the foil and emit high-energy, high-density γ-rays via nonlinear Compton scattering. The simulation results show that compared with the other two targets, target 3 affords better focusing of the laser field and electrons, which decreases the divergence angle of γ-photons. Consequently, denser and brighter γ-rays are emitted when target 3 is used. Specifically, a dense γ-ray pulse with a peak brightness of 4.6×10²⁶ photons/s/mm²/mrad²/0.1%BW (at 100 MeV) and 1.8×10²³ photons/s/mm²/mrad²/0.1%BW (at 2 GeV) are obtained at a laser intensity of 8.5×10²² W/cm² when the plasma density is equal to the critical plasma density n_c. In addition, for target 3, the effects of plasma channel length, foil curvature radius, laser polarization, and laser intensity on the γ-ray emission are discussed, and optimal values based on a series of simulations are proposed.