Classification and Definition of Polarizers

Polarizers are currently divided into the following categories:

1. Linear polarized light

During the propagation of light, there is only one type of vibration that remains in the same plane, and this type of light is called linearly polarized light (or plane polarized light). You can imagine what it's like through an experiment: you tie one end of a rope to a tree in your neighbor's yard and hold the other end in your hand. Assuming the rope passes through the center of two bamboo poles on the fence. If you vibrate the rope up and down now, the waves generated by the rope will pass between two bamboo shoots and be transmitted from your hand to that tree. At this moment, that fence is a barrier to your waves; Transparent;. However, if you make the rope sway left and right, it will collide with two bamboo poles, and the waves will not pass through the fence. At this point, the fence acts as a polarizing device.

2. Partially polarized light

Light waves contain transverse vibrations in all possible directions, but the amplitude varies in different directions. The amplitude has a maximum and minimum value in two perpendicular directions, and this type of light is called partially polarized light. Natural light and partially polarized light are actually composed of many linearly polarized lights with different vibration directions. When light enters a medium from air (strictly speaking, vacuum), the tangent of the Brewster angle is equal to the refractive index n of the medium. Since the refractive index of the medium is related to the wavelength of light, for the same medium, the magnitude of the Brewster angle is also related to the wavelength of light. Calculated based on the refractive index of optical glass of 1.4-1.9, the Brewster angle is approximately 54-62 degrees. When the incident angle deviates from the Brewster angle, the reflected light will be partially polarized light.

3. Elliptical polarized light

In the process of light propagation, the electric vectors at each point in space rotate around the axis of the light ray, and the endpoints of the electric vectors trace an elliptical trajectory. This type of light is called elliptically polarized light. When viewed in the direction of light, any electric vector that rotates clockwise is called right-handed elliptically polarized light, and any vector that rotates counterclockwise is called left-handed elliptically polarized light. The rotating electric vector in elliptically polarized light is the result of the vibration synthesis of two electric vectors with the same frequency, perpendicular vibration directions, and a fixed phase difference (see waveplate).

4. Circularly polarized light

The light with a circular trajectory traced by the endpoint of a rotating electric vector is called circularly polarized light, which is a special case of elliptically polarized light. After averaging over our observation period, circularly polarized light appears to be similar to natural light. However, the polarization direction of circularly polarized light changes according to a certain pattern, while the polarization direction of natural light changes randomly and without regularity.