Basic structure of a laser

March 11, 2022
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1. Laser working medium

The generation of laser must choose a suitable working medium, which can be normal, liquid, solid or semiconductor. Population inversion can be achieved in this medium to create the necessary conditions for obtaining laser light. Obviously, the existence of metastable energy levels is very beneficial to the realization of the population inversion world. There are nearly 1,000 working media, and the laser wavelengths that can be generated include a wide range of vacuum ultraviolet and far infrared.

As the core of the laser, it is composed of activated particles (both metals) and the matrix. The energy level structure of the activated particles determines the spectral characteristics and fluorescence lifetime of the laser and other laser characteristics, and the matrix mainly determines the physical and chemical properties of the working substance. According to the energy level structure of the activated particles, it can be divided into three-level systems (such as ruby ​​lasers) and four-level systems (such as Er:YAG lasers). There are four commonly used shapes of working substances: cylindrical (the most used at present), flat, disc and tubular.

2. Incentive source

In order to make the particle number inversion appear in the working medium, a certain method must be used to excite the atomic system to increase the number of particles in the upper energy level. Generally, gas discharge can be used to use electrons with kinetic energy to excite the atoms of the medium, which is called electrical excitation; pulsed light sources can also be used to irradiate the working medium, which is called optical excitation; and thermal excitation, chemical excitation, etc. Various types of excitation are visualized as pumping or pumping. In order to continuously obtain the laser output, it is necessary to constantly "pump" to maintain more particles in the upper energy level than in the lower energy level.

3. Concentrating system

There are two functions of the concentrating cavity, one is to effectively couple the pump source with the working material; the other is to determine the distribution of the pump light density on the laser material, thereby affecting the uniformity, divergence and optical distortion of the output beam . Both the working substance and the pump source are installed in the condensing cavity, so the quality of the concentrating cavity directly affects the pumping efficiency and performance. The elliptical cylindrical condenser cavity is the most commonly used in small solid-state lasers.

4. Optical resonator

It is composed of total reflection mirror and partial reflection mirror, which is an important part of solid-state laser. In addition to providing optical positive feedback to maintain the continuous oscillation of the laser to form stimulated emission, the optical resonator also restricts the direction and frequency of the oscillating beam to ensure high monochromaticity and high directivity of the output laser. The optical resonator of the most simple and commonly used solid-state laser is composed of two plane mirrors (or spherical mirrors) placed opposite to each other.

5. Cooling and filter system

Cooling and filtering systems are essential auxiliary devices for lasers. Solid-state lasers will produce serious thermal effects when working, so cooling measures are usually taken. It is mainly to cool the laser working material, pump system and concentrating cavity to ensure the normal use of the laser and the protection of the equipment. Cooling methods include liquid cooling, gas cooling and conduction cooling, but currently the most widely used method is liquid cooling. To obtain a laser beam with high monochromaticity, the filter system plays an important role. Filter system? It can filter most of the pump light and some other interference light, so that the output laser monochromaticity is very good.