再谈半波损失和薄膜干涉

本文的主要内容有四点.一是对近期本刊发表的《光由光密介质射向光疏介质时半波损失的条件》作补充讨论,给出一些数学公式上的解释和相应的物理情景.二是讨论该文中谈到的一些关于半波损失的看法,并指出当偏振平行于入射面的光从光密介质入射到光疏介质、且光密介质折射率远大于光疏介质折射率时,一般不会有半波损失.三是给出薄膜干涉的定量计算结果,展示了在通常情况下,教科书上的薄膜干涉公式结果与按菲涅耳公式计算的结果是非常接近的.四是指出,教科书上的薄膜干涉公式所指示的暗纹条件恰好是正确的,但对于亮纹条件,在某些情况下,该公式会得出完全错误的结果.     

折射率梯度引起反转的光自旋霍尔效应研究

从经典电动力学出发,研究了由折射率梯度导致的反转光自旋霍尔效应。通过分析光从光疏介质入射到光密介质和从光密介质入射到光疏介质两种情况,揭示了光自旋霍尔效应中的横移与偏振态、折射率梯度以及入射角等因素的定性关系。当入射角一定时,光从光疏介质入射到光密介质时的水平偏振横移绝对值大于垂直偏振横移,而从光密介质入射到光疏介质的情况正好与之相反,并且传输场的横移方向取决于折射率梯度方向,增大入射角能明显增强光自旋霍尔效应,对某一特定的线偏振光束,其左、右旋圆偏振光分量的横移等值反向。这些研究结果为调控光自旋霍尔效应提供了有效途径。     

基于传输矩阵法讨论光疏介质表面的全反射

探究了光在光密介质与超薄光疏介质界面处的全反射,通过在光密介质中嵌入一光疏介质薄层,利用传输矩阵法,定量地分析了入射角度以及光疏介质的厚度对反射率的影响.数值模拟结果表明,当光疏介质的厚度小于约一个波长时,即使入射角大于全反射的临界角,反射率也不一定会达到1,也就是说,光学隧道效应将会出现.     

利用光的全反射原理分析蜃景现象

光在均匀介质中是沿直线传播的,如果光介质的密度发生改变时,光路将随着发生改变．光线从光密介质射向光疏介质时,随着入射角的不断增大,折射角也不断地增大,并且折射光线的强度在减弱,反射光线的强度在增强如果介质的折射率为n．     

全反射现象及其在集成光学中的应用

当光从光密介质nl射向光疏介质n2(n1>n2),入射角θ1。逐渐增大到临界角θc=arc sinn2/n1时,继续增大θl,使θ1>θc,光线将全部被反射回入射光所在的介质,此时,光疏介质中完全没有折射光产生.这就是我们所熟知的光的全反射现象. 全反射是一种普通常见的光学现象.由于全反射时,入射光的全部能量完全被反射而没有折射损失,所以许多光学仪器都利用全反射来改变光线的传播方向和使象倒转;在新兴的光学领域──纤维光学和集成光学中也利用全反射来传导光能量. 然而,全反射现象的实际过程是相当复杂的,远非几何光学中所描述的那么简单.尽管全反射时…     

机械波在界面的反射、透射和半波损失

本文推导出了平面简谐波垂直入射时在界面上产生的反射波和透射波的表达式,并讨论波从波疏介质传播到波密介质产生的半波损失现象.有助于理工科学生理解机械波界面行为等相关物理概念和物理规律.     

关于光在反射时的半波损失问题

1.半波损失问题上所存在的矛盾在一般的光学教科书中,当讨论到反射光所产生的干涉现象时,例如,光驻波、洛埃镜、牛顿圈、迈克耳孙干涉仪等,必然会涉及光波在两种不同媒质界面上反射时的周相变更问题,即所谓“半波损失”问题。在光学教科书中,一般沿用这样的一个概念:光在光疏媒质(如空气)中传播,遇到光密媒质(如玻璃)而     

浅析海市蜃楼的成因

 海市蜃楼是一种自然现象,但在被充分认识以前,往往被人们神秘化、甚至迷信化。其实海市蜃楼就是阳光在大气中折射而产生的一种光学现象。当一束光线从一种透明介质到达另一种透明介质时其线路会发生改变,这就是光的折射。如图1所示:ML为透明介质A、B的分界面,N为法线,θ1为入射角,θ2为折射角。设光在A中的速度为v1,在B中的速度为v2,由折射定律可得:sinθ1sinθ2=v1v2.我们通常把光速较快的介质叫光疏介质,把光速较慢的介质叫光密介质。由上面的式子可知:光线从光疏介质进入光密介质时,入射角大于折射角,光线折向法线。     

薄膜干涉中半波损失的"例外

利用相位变化关系详细分析了薄膜处在上下界面不同的介质中时,两界面反射光有无半波损失的各种情况,得出了两界面性质相反时应有半波损失的情况下,却存在无半波损失的例外的结论.     

光波p分量在单轴晶体表面反射和折射的相位特性

根据单轴晶体的双折射和双反射性质,通过数值计算研究了光轴在入射面内并与晶体界面成任意角时光波p分量在单轴晶体表面反射和折射的相位特性.结果表明,光轴取向对相位变化有较大影响,光从光疏各向同性介质射入单轴晶体时,光轴方向改变反射光p分量的相位突变点,但对折射光p分量相位无影响.光从光密各向同性介质射入单轴晶体未发生全反射时,光轴方向同时影响p分量反射光和折射光的相位突变;发生全反射后,光轴方向影响反射光p分量的相位变化曲线.从单轴晶体出射到光疏各向同性介质未发生全反射时,光轴方向改变反射光p分量的相位跃变规律,折射光p分量在光轴方向和晶面成小角度时在布儒斯特角附近发生相位突变;发生全反射后,反射光p分量的相位变化曲线随光轴方向的改变发生较大变化.     

Acoustically induced transparency in optically dense resonance medium

It is shown that mechanical vibration (acoustical oscillation) of a solid medium along the propagation of multifrequency laser radiation enables one to control the resonant absorption. There exists an optimal spectral structure of the incident field dependent on vibration amplitude as well as the number and intensity of the frequency components that provides the full resonant transparency. A mechanism of the transparency is discussed. Transparency of this kind is shown to appear also via adiabatic modulation of the atomic transition frequency by an external microwave field.     

On photoelastic stress measurements in optically absorbing medium

The effects of optical absorption in a photoelastic medium on the formation of the fringe patterns are studied by taking into account the stress-induced anisotropy of both the refractive index and the absorption coefficient. The propagation of optical waves in a dielectric solid under the influence of stress is formulated by incorporating complex elasto-optical tensor elements in the wave equation. The expression for optical transmission from the plane polariscope configuration consisting of an absorbing photoelastic specimen is derived using the Jones calculus formalism including complex optical retardation terms. It is observed that the photoelastic fringe fields are substantially modified due to these effects which must be considered for accurate interpretation of the experimentally obtained fringes.     

Enhanced high harmonic generation from an optically prepared excited medium

We investigate high harmonics generated from rubidium atoms irradiated simultaneously by an intense 3.5 microm fundamental field and a weak cw diode laser. When 5p, 5d, and 4d excited states are populated through cascade excitation or deexcitation, orders-of-magnitude increases in harmonic yield as compared with the ground state are observed. It appears that, quite unexpectedly, the population accumulated in the 4d state alone is responsible for the observed enhancement.     

Enhancement of circular differential deflection of light in an optically active medium

In this letter, we investigate the circular differential deflection of a light beam refracted at the interface of an optically active medium. We show that the difference between the angles of deviation of the two circularly polarized components of the transmitted beam is enhanced manyfold near total internal reflection, which suggests a simple way of increasing the limit of detection of chiro-optical measurements.     

Coherent effects in ultrashort pulse propagation through an optically thick three-level medium

A theoretical study is made of the propagation of a weak ultrashort pulse through an optically thick, inhomogeneously broadened three-level medium of the V configuration driven by a self-induced transparency pulse on the coupled transition. The weak coherent pulse experiences a greatly enhanced transparency. The new transparency effect is discussed in detail and the results are found to be in good agreement with recent experimental observations. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 5, 359–363 (10 September 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Compensation of the optically induced Lorentz force in a homogeneous optical medium

It is shown on the basis of different approaches that the density of optically induced forces applied to a homogeneous optical medium embedded in a simplest 1D structure in a form of a plane optical resonator is equal to zero. In particular, the density forces calculated on the base of the energetic approach, where no assumptions about physical nature of optically induced forces are used, are also equal to zero. At the same time the same forces calculated by means of the approach based on the Lorentz force are different from zero. A conclusion is derived that there is an additional type of optically induced force which compensates the Lorentz density forces. Thus, the Lorentz force approach used for calculation of the density of optically induced force is inconsistent.