北京理工大学819物理光学考研课件7教程.ppt

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1、E EB Bk k第六章第六章 光的偏振和晶体光学基础光的偏振和晶体光学基础WaveplatePolarizerPolarizer6.3 6.3 偏振光的产生、转换和检验偏振光的产生、转换和检验6.3.1 6.3.1 线偏振光的产生和检验线偏振光的产生和检验d理硕教育专注于北理工考研辅导本资料由理硕教育整理，理硕教育是全国本资料由理硕教育整理，理硕教育是全国唯一专注于北理工考研辅导的学校，相对唯一专注于北理工考研辅导的学校，相对于其它机构理硕教育有独有的优势。丰富于其它机构理硕教育有独有的优势。丰富的理工内部资料资源与人力资源确保每个的理工内部资料资源与人力资源确保每个学员都受益匪浅，确保了理

2、硕教育的学员学员都受益匪浅，确保了理硕教育的学员初试通过率初试通过率89%以上，复试通过率接近以上，复试通过率接近100%，理硕教育全力助您圆北理之梦理硕教育全力助您圆北理之梦.网址网址1.1.线偏振光的产生线偏振光的产生（2 2）各种线偏器）各种线偏器When the reflected beam makes aright angle with the transmitted beam,and the polarization is parallel,then no scattering can occur,due to the scattered dipole emission patte

3、rn.But our right-angle assumption implies that q qi+q qt =90.So:Thus,Brewsters Angle RevisitedA complex trigonometric calcu-lation reveals that the reflectioncoefficient for parallel-polarizedlight goes to zero for Brewstersangle incidence,tan(qi)=nt/ninintqiqiqtqi+qt=90 折射式起偏器，玻璃堆折射式起偏器，玻璃堆The Pile

4、-of-Plates PolarizerAfter numerous Brewster-angle transmissions,mainly the parallel polarization remains.Unfortunately,only about 10%of the perpendicular polarizationis reflected on each surface,so you need a big pile of plates!Dielectric polarizersA multi-layer coating can also act as a polarizer.G

5、lass 二向色性起偏器二向色性起偏器,人造偏振片人造偏振片Polarizer transmitting vertical polarizationThis polarizer transmits horizontal polarization(of which there is very little).Wire Grid PolarizerThe light can excite electrons to move along the wires,which thenemit light that cancels the input light.This cannot happen per

6、pen-dicular to the wires.Such polarizers work best in the IR.Polaroid sheet polarizers use the same idea,but with long polymers.Input light contains both polarizationsWire grid polarizer in the visibleUsing semiconductor fabrication techniques,a wire-grid polarizer was recently developed for the vis

7、ible.The spacing is less than 1 micron.晶体线偏器晶体线偏器A.A.尼科尼科耳棱镜耳棱镜(Nicol)(Nicol)方解石方解石:尼科耳棱镜的工作原理尼科耳棱镜的工作原理 尼科耳棱镜的孔径角尼科耳棱镜的孔径角The Nicol Polarizer uses two identical prismsof calcite and TIR off a layer of optical cement.Snells Law separates the beams at the entrance.The perpendicular polarization then

8、goes from high index(1.66)to low(1.55)and undergoes total internal reflection,while the parallel polarization is transmitted near Brewsters angle.Combine two prisms of calcite(with parallel optical axes),glued together with Canada balsam cement(n=1.55).B.B.格兰格兰(Glan)(Glan)棱镜棱镜 思考题：格兰棱镜的反射光是什么偏振态？思考题

9、：格兰棱镜的反射光是什么偏振态？格兰棱镜产生线偏振光的原理格兰棱镜产生线偏振光的原理 Real PolarizersAir-spaced polarizers渥拉斯顿渥拉斯顿(Wollaston)(Wollaston)棱镜棱镜(a)(a)和罗雄和罗雄(Rochon)(Rochon)棱镜棱镜(b)(b)产生两束空间分离的线偏振光，偏振度好，但光能利用率低。产生两束空间分离的线偏振光，偏振度好，但光能利用率低。渥拉斯顿棱镜的工作原理渥拉斯顿棱镜的工作原理Wollaston Polarizing Beam SplitterThe ordinary and extraordinary rays hav

10、e different refractive indicesand so diverge.The Wollaston polarizing beam splitter uses two rotatedbirefringent prisms,but relies only on refraction.罗雄棱镜的工作原理罗雄棱镜的工作原理2.2.线偏振光检验线偏振光检验马吕斯马吕斯(Malus)(Malus)定律定律(2)(2)线偏振光的检验线偏振光的检验(3)(3)半影式检偏器半影式检偏器6.3.2 6.3.2 椭圆偏振光的产生和波片椭圆偏振光的产生和波片WaveplatePolarizerPo

11、larizer1.1.椭圆偏振光椭圆偏振光(包括园偏光）包括园偏光）产生的途径分析产生的途径分析2 2波片波片(1)(1)波片的概念波片的概念dd波片的色差波片的色差d消色差波片消色差波片 d(2)(2)几种常用的单块式波片几种常用的单块式波片 dThickness of wave platesWhen a wave plate has less than 2p relative phase delay,we say its a zero-order wave plate.Unfortunately,they tend to be very thin.Solve for d to find t

12、he thickness of a zero-order quarter-wave plate:Using green light at 500 nm and quartz,whose refractive indices are ne no=1.5534 1.5443=0.0091,we find:This is so thin that it is very fragile and very difficult to manufacture.dd =13.7 mmMulti-order wave platesA multi-order wave plate has more than 2p

13、 relative phase delay.We can design a twentieth-order quarter-wave plate with 20 waves of relative phase delay,instead of just:This is thicker,but its now 41 times more wavelength dependent!Its also temperature dependent due to ns dependence on temperature.dd =561 mm波片的波片的“快轴快轴”和和“慢轴慢轴”方向方向 正单和负单轴晶体

14、制成的波片，快轴和慢轴方向相反正单和负单轴晶体制成的波片，快轴和慢轴方向相反(3)(3)附加位相差可调节的波片补偿器附加位相差可调节的波片补偿器(a)(a)巴比内补偿器巴比内补偿器 (b)(b)索列尔补偿器索列尔补偿器The Babinet Compensator rotates polarization by an arbitrary amount.Top wedge is cut with fast and slow axes opposite to those of bottom wedge.Slide one wedge with respect to the other,changi

15、ng d1 and/or d2.In practice,the two wedges are contacted.Inputbeamd2Optic axesxyzOutputbeamd1d1The Babinet Compensator rotates polarization by an arbitrary amount.Top wedge is cut with fast and slow axes cut opposite to those of bottom wedge.Slide one wedge with respect to the other,changing d1 and/or d2.Note that this motion doesnt displace the beam!InputbeamTop wedgeBottom wedge第十讲作业题第十讲作业题（5月月27日）日）习题习题 6.13 6.13 习题习题 6.146.14习题习题 6.15 6.15 习题习题 6.166.16Thank youThank you