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1、5.双折射双折射 Double Refraction 1)双折射现象双折射现象 unpolarized light自然光自然光O光光e-光光双折射双折射双折射双折射双折射双折射 calcite方解石方解石The“double-bending”of a beam transmittedthrough calcite,is called double refraction.2)the ordinary ray(O-ray)and the extraordinary ray(e-ray).(1687年惠更斯研究)年惠更斯研究)a)two beams are polarized light with
2、their planes of vibration at right angles to each other.O光光e光光b)O-ray obey the refraction law.The crystal has a single index of refraction no.c)The e ray index of refraction varies with direction from no to a smaller value (for calcite)ne.(与入射角有关与入射角有关 且不为定值)且不为定值)对对O光:光:对对e光:光:(与入射角无关与入射角无关 且为定值)且为
3、定值)e光在晶体中传播,光在晶体中传播,光速是一变值。光速是一变值。为什么?为什么?自然光自然光方解石方解石3)optic axis 光轴光轴787868102a)optic axis 光轴光轴-光轴光轴The direction at which a beam transmitted through calcite without double refraction called optic axis.b)The optic axis is found by erecting a line at either of the two corners where three obtuse ang
4、les meet(the“blunt”corners),making equal angles 68 with the crystal edges.Any line in the crystal parallel to this line is also an optic axis.光轴光轴4)principal section 主截面主截面The principal section is consist of the normal to crystal surface and optic axis.Any section in the crystal parallel to this sec
5、tion is also the principal section.注意:注意:when incident ray lie in the principal section,the vibration of O-ray normal to the principal section and the vibration of e-ray parallel to the principal section.102787878光轴光轴入射面在主截面内时,入射面在主截面内时,o光光e光的振动面互相垂直光的振动面互相垂直Two planes of vibration at right angles t
6、o each other.且且o光为振动面垂直光为振动面垂直于主截面的偏振光;于主截面的偏振光;e光为振动面平行于光为振动面平行于主截面的偏振光;主截面的偏振光;5)正晶体与负晶体)正晶体与负晶体Positive crystal and negative crystal Negative crystal:ne no78786)用惠更斯原理解释双折射现象)用惠更斯原理解释双折射现象因因O光沿各向传播的速度是相同的,故光沿各向传播的速度是相同的,故O光的波面是球面。光的波面是球面。而而e光在晶体内沿各向传播的光在晶体内沿各向传播的速度不相同,所以速度不相同,所以e光的波面光的波面 是椭球面。是椭球
7、面。正晶体正晶体-负晶体负晶体-在晶体内一个点波在晶体内一个点波源发光的波阵面:源发光的波阵面:78光轴光轴正晶体正晶体负晶体负晶体o光光e光光光轴光轴(负晶体)(负晶体)incident ray lie in the principal section:A)There is a angle between optic axis and crystal surface 光轴与晶体表面有一夹角(正入射光轴与晶体表面有一夹角(正入射)自然光自然光optic axis光轴光轴 B)optic axis is parallel to the crystal surface 光轴与晶体表面平行(正入射)
8、光轴与晶体表面平行(正入射)自然光自然光o光光e光光光轴光轴O e 二光通过厚度二光通过厚度d的光程差:的光程差:四分之一波片四分之一波片二分之一波片(半波片)二分之一波片(半波片)结论:结论:有双折射。有双折射。自然光自然光o光光e光光光轴光轴C)optic axis is normal to the crystal surface 光轴与晶体表面垂直(正入射)光轴与晶体表面垂直(正入射)(负晶体)(负晶体)无双折射现象无双折射现象o光光e光光晶体晶体光轴光轴光轴光轴D)There is a angle between optic axis and crystal surface 光轴与晶体
9、表面有一夹角(斜入射)光轴与晶体表面有一夹角(斜入射)AABCC7)polarizing prism 偏振棱镜偏振棱镜自然光自然光光轴光轴6871 WNicol prism 尼科尔棱镜(尼科尔棱镜(1928年)年)no=1.658ne=1.486o光光e光光N加拿大加拿大=1.550O光以光以76入射到入射到加拿大加拿大树胶,产生树胶,产生全反射后被吸收。全反射后被吸收。76e光出射成为偏振光光出射成为偏振光ACCalcite方解石方解石ADCB光光轴轴光轴光轴o光光e光光O光光e光光Wouaston prism 渥氏棱镜渥氏棱镜光轴光轴o光光e光光when incident ray lie
10、in the principal section,the vibration of O-ray normal to the principal section and the vibration of e-ray parallel to the principal section.O、e二光通过晶体二光通过晶体后被分得很开,从后被分得很开,从而获得偏振光。而获得偏振光。8)Applications of polarization 偏振光的应用偏振光的应用汽车车灯与窗玻璃用同一偏振化方向的透明膜汽车车灯与窗玻璃用同一偏振化方向的透明膜a)防止对面来的灯光耀眼防止对面来的灯光耀眼2)放立体电影)放立体电影原理:利用人眼的双眼效应原理:利用人眼的双眼效应作业:作业: