Polarized direction Part 3 Polarization of light

§17-11 Polarization state of light F Polarized state:the oscillating state of light vector.  Natural light  Plane polarized light  Partially polarized light  Elliptically polarized light  Circularly polarized light F The electric field vector in electromagnetic wave are sensitive for most detectors. -- -vector is called light vector. -- -vector is called light vector.Classification F Electromagnetic wave is transverse wave

1. Natural light (Unpolarized light) F The amplitudes of light vectors along all directions at the plane which is perpendicular to the direction of propagation have same magnitude.

2. Plane polarized light ( 线偏振光 or 平面偏振光 ) F The oscillating direction of light vector is always located in a fixed plane. Oscillating plane Light vector

3. Partially polarized light ( 部分偏振光 ) F The amplitudes of light vectors along all directions at the plane which is perpendicular to the direction of propagation have different magnitude.

The end of the light vector moves with constant speed in a circle, or in an ellipse. 4. Circularly or Elliptically polarized light ( 圆 or 椭圆偏振光 ) ( 圆 or 椭圆偏振光 )

Poleroid §17-12 Polarization of light Law of Malus I. Polarizing and polarization analyzing ( 起偏和检偏 ) F Polaroid ( 偏振片 ) Polarizing direction F Polarizing direction ( 偏振化方向 ) ： permitting the light vector passing through.

F Polarization analyzing--to test whether the incident light is polarized. F Polarizing--natural light  polarizer  plane polarized light polarizer analyzer

II. Malus law ----Malus law A 1, A 2 —amplitudes of the polarized light.

  =0 or  =180 0, I 2 =I 1 -- maximum Discussion ：   =90 0 or  =270 0, I=0 -- minimum I1I1I1I1 I2I2I2I2

[Example] Two polarizing sheets are put parallely. Their polarized directions have the angle Calculate when the natural light is incident on the polaroids normally, the intensity ratio of transmitting and incident light. (discuss two cases:  the polaroids have not absorption  the polaroids have 10% ratio of absorption.)

Solution ：  no absorption Assume the intensity of incident natural light is I 0. The light is fully polarized after passing P 1. The polarized direction is parallel to P 1 and the intensity is After I 1 passes through P 2, its polarized direction is parallel to P 2 and the intensity is

 the absorption ratio equals to 10%

§17-13 Polarization by Reflection and Refraction I. Partially polarization phenomenon F When a natural light is incident on a interface of two kinds of materials, its reflected light and refracted light are partially polarized light. F characteristic ： for reflected light, the perpendicular component is larger than parallel component. Refracted light is converse.

II. Brewster law F When i equals to a special angle i 0 ， the reflected light is fully polarized light with the polarized direction perpendicular to the incident plane. Brewster angle In this case ----Brewster Law As 90 0

Notes  When i= i 0 ， the reflected light is fully polarized, the refracted light is partially polarized and has the maximum polarized degree.  The reflected light is of low intensity (15%),  Let a natural light passes through a stacking glass plates, the transmitted light is almost polarized. and the refracted light is of high intensity. and the refracted light is of high intensity.

§17-14 Double refraction I. Birefringence (Bi-refraction) phenomenon 双 折 射折 射 双 折双 折 双 折双 折 Calcite crystal o-ray e-ray Ordinary light (o-ray): follows Refraction Law. Extraordinary light(e-ray): does not follow Refraction Law. 双折射

When the crystal rotates round the incident light ， o-ray is fixed and e-ray rotates round o-ray.

II. Characteristic of birefringence of light 1. Some concepts of crystallography F Optical axis ： it represents a direction that there is no birefringence phenomenon when a light travels along this direction l Uniaxial crystal---it has one optical axis only ( calcite 方解石、 石英 ) l Uniaxial crystal---it has one optical axis only ( calcite 方解石、 quartz 石英 ) Biaxial crystal --- it has two optical axes ( ) Biaxial crystal --- it has two optical axes (mica 云母 sapphire 蓝宝石 )

F Principal plane （主平 面） ： the plane formed by some ray (o-ray or e-ray) and optical axis. optical axis normal o-ray e-ray F If the optical axis is not at the incident plane, the principle planes of e-ray and o-ray are not coincide. In the crystal.

 O-ray and e-ray are plane polarized light. 2. Characteristics  The oscillating direction of o-ray  its principle plane. The oscillating direction of e-ray  its principle plane. The oscillating direction of e-ray  its principle plane. O-ray E-ray

 When the optical axis is located in the incident plane, the principle planes of o-ray and e-ray coincide. The oscillating directions of o-ray and e-ray are perpendicular to each other. o.A.

III. Explanation of birefringence phenomenon F Reason:The travel speed of o-ray in a birefringence crystal is homogeneous isotropic. The speed of e-ray is anisotropic. O-ray ： the wavefront is spherical surface. E-ray ： the wavefront is ellipic surface. positive crystal negative crystal

O.A. O.A. F The explanation of Huygens principle

O.A. O.A.

IV. Application of birefringence Nicle polarizing prism calcite crystal A cement from Canada tree

O.A.

I. The interference principle of polarized light polarizer analyzer natural light Birefringence film O.A. § The interference of polarized light 偏 振光的干涉 Polarized light Two coherent olarized lights

The polarized light behind P 1 is separated into o-ray and e-ray after it passes through the birefringence film. The phase difference between o-ray and e-ray is --their vibration directions  and  is constant. Their amplitudes are

Behind analyzer ： o-ray and e-ray have their vibration components on the polarized direction of P 2 : --equal amplitude, but opposite vibrating direction ( i.e. having extra phase difference .)

F The phase difference between two coherent polarized lights is When the thick of birefringence film is different, the interference fringes appear. The interference fringes of the polarized lights produced by quartz crystal edge.

II. Optical stress analysis analyzer polarizer Mechanical stress Mechanical stress --birefringence material

when the internal stress of a material is not uniform, the interference fringes will appear behind P 2. The experiment shows: k ： proportion factor ， p ： stress