The phenomenon of light interference and line emission shows that light is a wave, but these phenomena can not tell us whether light is P-wave or S-wave, and the polarization phenomenon of light clearly shows the S-wave property of light. Historically, as early as before the establishment of electromagnetic theory of light and not many years after the success of Young's double-slit experiment, Marius (E. L. Malus) discovered the polarization phenomenon of light in experiments in 1809.

I. the purpose of the experiment

1. Verify Marius' law;

2. Generate and observe the polarization state of light;

3. Understand the components and instruments that generate and test polarized light;

4. Master the conditions and methods of generating and testing polarized light.

II. the experimental instruments

Light source (incandescent lamp or visible light laser), polarizer, analyzer, optical screen or optical power indicator, 1/4 wave plate.

III. the experimental principle

Light wave is a kind of electromagnetic wave, electromagnetic wave is a shear wave, and the electrical vector in light wave is perpendicular to the propagation direction of wave. The polarization phenomenon of light clearly shows the shear wave property of light. The electrical vector E and the magnetic vector H of light waves are perpendicular to each other and both perpendicular to the propagation direction C of light (Fig. 1). Generally, the electric vector E represents the vibration direction of light, and the plane formed by the electric vector E and the propagation direction C of light is called the light vibration surface.

We know that light has five polarization states, namely linearly polarized light, elliptically polarized light, circularly polarized light, natural light and partially polarized light. In the process of propagation, the vibration direction of the electrical vector is always in a certain direction, which is called plane polarized light or linearly polarized light (Fig. 2A). The light emitted by a light source is composed of a large amount of molecular or atomic radiation. The light emitted by a single atom or molecule is polarized. Because of the thermal motion of a large number of atoms or molecules and the randomness of radiation, the probability of the vibration surface of the light emitted by them appearing in all directions is the same.

Generally speaking, the time averages of electrical vectors in all directions are equal within 10-6 seconds, so the light emitted by this light source does not show polarization to the outside, which is called natural light (Figure 2b). In the process of luminescence, the probability that the vibration surface of some lights appears in a specific direction is greater than that of other directions, that is, the electrical vector is stronger in a certain direction for a long time. Such lights are called partially polarized light (Fig. 2C). There are also some lights whose orientation of vibration surface and the size of electrical vector change regularly from time to time. The trajectory of the end of electrical vector in a plane perpendicular to the propagation direction is ellipse or circle. This kind of light is called elliptically polarized light or circularly polarized light (Fig. 3A). Among them, linearly polarized light and circularly polarized light can be regarded as special cases of elliptically polarized light.

Elliptically polarized light can be regarded as the combination of two linearly polarized lights whose vibration directions are perpendicular to each other propagating in the same direction z: as shown in Figure 1:

Where A is the amplitude, which is the circular frequency of the two light waves, T is the time, and K is the value of the wave vector, which is the relative phase difference between the two waves. The trajectory depicted by the end point of the composite vector E in the wavefront is an ellipse. The shape, orientation and direction of rotation of an ellipse, determined by the sum of Ax, Ay. When Ax = Ay and =/2, elliptically polarized light becomes circularly polarized light; When Ax (or Ay = 0) and = 0 or, elliptically polarized light becomes linearly polarized light (as shown in fig. 3b).

In this experiment, we mainly investigate the changes of various polarization states of light.

IV. Technical indicators

Optical experimental guide rail: 800mm,

Semiconductor laser: 650nm, 4mW.

Laser power indicator: three-bit semi-digital meter, measuring range: 200 μ W, 2mW, 20mW, 200mW, adjustable gears. Minimum resolution 0. 1u W

1/4 wave plate (including frame): 360-degree adjustable, minimum scale 1 degree, light aperture 23mm.

1/2 wave plate (including frame): 360-degree adjustable, minimum scale 1 degree, light aperture 23mm.

Shi Ying optical rotation accessories (including frame): three-dimensional, 360-degree adjustable, minimum scale 1 degree, light aperture 23mm, thickness 3mm.

V. Characteristics of instruments

The high stability semiconductor laser is used as the light source, which effectively solves the errors caused by the fluctuation of light intensity and the change of polarization state in the measurement process. In the power measurement range, the use of adjustable range is beneficial to eliminate the shift error, and the adjustable range has unique advantages in relative light intensity measurement, such as power change measurement and light intensity distribution measurement

VI. Complete set of equipment

Optical experimental guide rail, semiconductor laser, polarizer, 1/4 wave plate, 1/2 wave plate, Shi Ying optical rotation accessory, laser power indicator, etc.