Laser is polarized light, the laser is monochromatic linear polarized light, and infrared polarized light is wide spectrum elliptically polarized light, which is similar to the composite application of low power laser in different bands.
When the electron in the atom absorbs the energy, it transits from the low energy level to the high energy level and then falls back from the high energy level to the low energy level, the released energy is released in the form of photons. The optical properties of photons in the induced (excited) photon beam (laser) are highly consistent. This makes the laser better monochromatic, bright, and directional than the ordinary light sources.
The asymmetry of vibration direction to propagation direction is called polarization, which is the most obvious sign that S-wave is different from other P-waves. Lightwave is an electromagnetic wave, so the propagation direction of a light wave is the propagation direction of the electromagnetic wave.
The electric vibration vector E and the magnetic vibration vector h in the light wave are perpendicular to the propagation velocity V, so the light wave is a transverse wave with polarization. Polarized light is called polarized light.
The mechanism of polarized light generation is as follows
Plane polarized light can be obtained by reflection, multiple refraction, birefringence, and selective absorption. A polarizer with selective absorption can be used to generate plane-polarized light.
The polarizer is a kind of thin film made by the artificial method. It is made by using a special method to make the particle crystals with strong selective absorption arranged regularly in the transparent adhesive layer. It allows the light passing through a certain electric vector vibration direction (this direction is called polarization direction) to absorb the light perpendicular to it.
Therefore, after the natural light passes through the polarizer, the transmitted light basically becomes plane-polarized light. The polarizer is widely used because it is easy to make.
At present, there are two kinds of fiber laser oscillators that produce linearly polarized laser. One is the linear polarization fiber laser oscillator with spatial structure, the other is the linear polarization fiber laser oscillator with all fiber structures. The linear polarization laser oscillator with spatial structure has some disadvantages, such as complex structure, poor stability, easy to produce end face damage, and so on.
There are two ways to realize the all-fiber linear polarization laser oscillator. One is to weld two polarization-maintaining gratings orthogonally, so that the reflection peaks of one pair of fast and slow axes overlap and the other pair of fast and slow axes stagger, so as to ensure that there is only one polarization mode oscillation.
Researchers have realized the output from 100 MW to 100 W, but this method requires the grating parameters matching and strict control of the influence of temperature on the grating characteristics. Another way is to suppress the high-order mode and one of the polarization modes by bending the gain fiber so that the laser oscillator can achieve linear polarization single-mode output.
In this paper, the application prospect of polarized laser is illustrated by underwater imaging and medical applications.