1. Laser working medium
The production of lasers must choose a suitable working medium, which can be ordinary body, liquid, solid or semiconductor. In this medium, the population can be reversed, creating the necessary conditions for obtaining lasers. Obviously, the existence of metastable energy levels is very beneficial to the realization of the population inversion world. There are nearly a thousand kinds of working media, and the laser wavelengths that can be generated include a wide range of far infrared to vacuum ultraviolet.
As the core of the laser, it consists of two parts: activated particles (all of which are metal) and the matrix. The energy level structure of the activated particles determines the spectral characteristics and fluorescence lifetime of the laser. The matrix mainly determines the physical and chemical properties of the working material. According to the energy level structure of the activated particles, it can be divided into a three-level system (such as a ruby laser) and a four-level system (such as an Er:YAG laser). Currently, there are mainly four kinds of commonly used working materials: cylinder (currently used most), flat plate, disc and tube.
2. Incentive sources
In order to cause population inversion in the working medium, some 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, and electrons with kinetic energy are used to excite medium atoms, which is called electrical excitation; pulsed light sources can also be used to illuminate the working medium, which is called optical excitation; there are thermal excitation, chemical excitation, and so on. The various incentive methods are visually called pumping or pumping. In order to continuously obtain laser output, it must be continuously "pumped" to keep more particles of higher energy levels than particles of lower energy levels.
3. Concentration system
The condensing cavity has two functions, one is to effectively couple the pump source and the working medium; 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. The working fluid and pump source are installed in the concentration chamber, so the quality of the concentration chamber directly affects the efficiency and working performance of the pump. The elliptical cylindrical condenser cavity is the most commonly used small solid-state laser.
4. Optical cavity
Composed of a total reflection mirror and a partial reflection mirror, it is an important part of a solid-state laser. In addition to providing positive optical feedback to keep the laser continuously oscillating to form stimulated emission, the optical resonant cavity also limits the direction and frequency of the oscillating beam to ensure high monochromaticity and high directivity of the output laser. The simplest and most commonly used optical resonator for solid-state lasers is composed of two plane mirrors (or spherical mirrors) placed opposite each other.
5. Cooling and filtering system
Cooling and filtering systems are essential auxiliary equipment for lasers. Solid-state lasers produce more serious thermal effects during operation, so cooling measures are usually taken. The main purpose is 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 the most widely used method is liquid cooling. In order to obtain a laser beam with high monochromaticity, the filter system plays a very important role. The filter system can filter out most of the pump light and some other interference light, so that the output laser has a very good monochromaticity.
The basic structure of the laser
1. Laser working medium