Principle and application of polarizer

The principle and application of polarizer are as follows:

First, the principle of polarizer

Polarizer is a kind of thin film made by artificial method, which is made of fine particles with strong selective absorption arranged regularly in a transparent adhesive layer by special method. It allows the light passing through a certain electric vector vibration direction (this direction is called polarization direction) to absorb the light vibrating perpendicular to it, that is, it has dichroism.

So after natural light passes through the polarizer, the transmitted light basically becomes plane polarized light. Generally speaking, the damage threshold of polarizer is small, and P polarized light and S polarized light cannot be separated.

Because people's eyes can't directly distinguish polarized light, in experiments, polarizers are often used to play the role of polarizers or analyzers: when the polarizer rotates once and the light spot is bright and black, it is linear polarized light.

When the polarizer rotates once and the brightness of the light spot is strong and weak, it is elliptically polarized light. When the polarizer rotates and the spot brightness remains unchanged, it may be unpolarized or circularly polarized. At this time, it is usually necessary to use 1/4 wave plate or other vibration elements for auxiliary detection.

Second, the application of polarizer

1, stereoscopic film

When shooting a three-dimensional movie, two cameras are used. The lenses of two cameras are equivalent to two human eyes. They take two portraits of the same object at the same time, and both portraits are reflected on the screen at the same time. If one eye of the audience can only see one of the pictures, it can give the audience a three-dimensional sense.

Therefore, during the screening, a polarizer is placed on the lens of each of the two players, and the polarization directions of the two polarizers are perpendicular to each other. Spectators wear glasses made of polarizers. The polarization direction of the left-eye polarizer is the same as that of the left-handed player, and the polarization direction of the right-eye polarizer is the same as that of the right-handed player.

In this way, the two pictures on the screen are observed through two eyes respectively, and a three-dimensional image is formed in people's minds.

2. Application of machine vision

In visual inspection, partial polarization caused by the reflection of metal and insulating surface, specular reflection, that is, reflection, affects the inspection.

So we can add a polarization filter in front of the camera and adjust the direction to suppress some polarization. However, because unpolarized light is only partially polarized after reflection, a better way to suppress partial reflection is to first turn light into polarized light and then illuminate the surface of the object.

In this way, we use two polarizers, one on the lens and one on the light source. The polarizer installed on the lens plays the role of analyzer (detecting polarized light), and the polarizer on the light source plays the role of polarizer (changing natural light into polarized light). So as long as the analyzer and polarizer are 90 degrees, the polarized light generated by reflection will be completely suppressed.