［精选PPT］双折射现象.ppt

5. 双折射 Double Refraction
1) 双折射现象
unpolarized light
自然光
O光
e-光
双折射
双折射
双折射
calcite
方解石
The “double-bending” of a beam transmitted
through calcite, is called double refraction.
2)the ordinary ray (O-ray) and the extraordinary
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.
O光
e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
且不为定值)
对O光:
对e光:
(与入射角无关
且为定值)
e光在晶体中传播,光速是一变值。
为什么?
自然光
方解石
3)optic axis 光轴
78º
78º
68º
102º
a)optic axis 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 angles meet (the “blunt ” corners),
making equal angles 68º with the crystal edges.
Any line in the crystal parallel to this line is also
an optic axis.
光轴
4)principal section 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 section is
also the principal section.
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.
102º
78º
78º
78º
光轴
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
Negative crystal: ne < no
Positive crystal: ne > no
78º
78º
6)用惠更斯原理解释双折射现象
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--
在晶体内一个点波
源发光的波阵面:
78º
光轴
正晶体
负晶体
o光
e光
光轴
(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)
自然光
optic axis
光轴
B) o