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5. 双折射 Double Refraction

5. 双折射 Double Refraction. unpolarized light 自然光. 1) 双折射现象. e- 光. calcite 方解石. O 光. 双折射. The “double-bending” of a beam transmitted through calcite, is called double refraction. 2 ) the ordinary ray (O-ray) and the extra ordinary ray (e-ray). ( 1687 年惠更斯研究).

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5. 双折射 Double Refraction

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  1. 5. 双折射 Double Refraction unpolarized light 自然光 1) 双折射现象 e-光 calcite 方解石 O光 双折射 The “double-bending” of a beam transmitted through calcite, is called double refraction. 2)the ordinary ray (O-ray) and theextraordinary ray (e-ray).(1687年惠更斯研究) a)two beams are polarized light with their planes of vibration at right angles to each other.

  2. 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. 自然光 e光在晶体中传播,光速是一变值。 (与入射角无关 且为定值) e光 O光 方解石 对O光: 为什么? 对e光: (与入射角有关 且不为定值)

  3. 78º 68º 102º 78º 3)optic axis 光轴 The direction at whicha beam transmitted through calcite without double refraction calledoptic axis. a)optic axis 光轴--- b) The optic axis is found by erecting a line at either of the two corners where three obtuse angles meet (the “blunt ” corners), 光轴 making equal angles 68º with the crystal edges. Any line in the crystal parallel to this line is also an optic axis.

  4. 78º 102º 78º 4)principal section 主截面 The principal section is consist of the normal to crystal surface and optic axis. 注意: Any section in the crystal parallel to this sectionis also the principal section. 光轴 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.

  5. 78º 78º 入射面在主截面内时,o光e光的振动面互相垂直 Two planes of vibration at right angles to each other. 且o光为振动面垂直 于主截面的偏振光; e光为振动面平行于 主截面的偏振光; 5)正晶体与负晶体 Positive crystal and negative crystal 光轴 Positive crystal: ne > no Negative crystal: ne < no

  6. 6)用惠更斯原理解释双折射现象 光轴 78º 光轴 78º 因O光沿各向传播的速度是相同的,故O光的波面是球面。 而e光在晶体内沿各向传播的 速度不相同,所以e光的波面 是椭球面。 正晶体-- 负晶体-- e光 o光 在晶体内一个点波 源发光的波阵面: 负晶体 正晶体

  7. incident ray lie in the principal section: (负晶体) optic axis 光轴 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 ) 自然光

  8. B) optic axis is parallel to the crystal surface 光轴与晶体表面平行(正入射) 有双折射。 结论: 光轴 自然光 o光 e光 O e 二光通过厚度d的光程差: 四分之一波片 二分之一波片(半波片)

  9. 无双折射现象 (负晶体) C) optic axis is normal to the crystal surface 光轴与晶体表面垂直(正入射) 自然光 光轴 o光 e光

  10. 光轴 光轴 D) There is a angle between optic axis and crystal surface 光轴与晶体表面有一夹角(斜入射) 晶体 e光 o光

  11. B 光轴 N加拿大=1.550 A A’ A 76º CC’ 71º B 68º C D 7)polarizing prism 偏振棱镜 W·Nicol prism 尼科尔棱镜( 1928年) e光 A’ 自然光 no=1.658 ne=1.486 o光 C’ O光以76º入射到加拿大树胶,产生 全反射后被吸收。 Calcite 方解石 e光出射成为偏振光

  12. Wouaston prism 渥氏棱镜 when incident ray lie in the principal section, the vibration 光轴 光 轴 光轴 of O-ray normal to the principal section and the vibration of e-ray parallel to the principal section. e光 e光 o光 e光 O光 O、e二光通过晶体 后被分得很开,从 而获得偏振光。 o光

  13. 8)Applications of polarization 偏振光的应用 a) 防止对面来的灯光耀眼 汽车车灯与窗玻璃用同一偏振化方向的透明膜

  14. 作业: 2)放立体电影 原理:利用人眼的双眼效应 返回

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