Basic Structure of the Laser

1. Laser working medium

The laser must be produced by selecting a suitable working medium, which can be a normal body, a liquid, a solid or a semiconductor. In this medium, particle number inversion can be achieved to produce the necessary conditions for obtaining a laser. Obviously, the existence of the metastable energy level is very advantageous for realizing the population reversal. There are nearly a thousand working media available, and the laser wavelengths that can be generated include the far infrared from the vacuum ultraviolet ray, which is very extensive.

 As the core of the laser, it consists of activated particles (both metal) and matrix. The energy level structure of the activated particles determines the laser characteristics such as the spectral characteristics and fluorescence lifetime of the laser. 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 a three-level system (such as a ruby laser) and a four-level system (such as an Er:YAG laser). There are four main types of working materials currently used: cylindrical (currently used most), flat, disc-shaped and tubular. 

2. Incentive source 

In order to cause the population inversion in the working medium, the atomic system must be excited by a certain method to increase the number of particles at the upper level. Generally, gas discharge can be used to excite electrons with kinetic energy to excite medium atoms, which is called electro-excitation; pulsed light sources can also be used to illuminate working medium, called photoexcitation; and thermal excitation, chemical excitation, and the like. Various incentives are visualized as pumps or pumping. In order to continuously obtain the laser output, it is necessary to constantly "pump" to maintain the number of particles at the upper level more than the lower level.

3. Concentrating system

The concentrating cavity has two functions, one is to effectively couple the pump source with the working substance; the other is to determine the distribution of the pumping optical 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 concentrating cavity, so the advantages and disadvantages of the concentrating cavity directly affect the efficiency and working performance of the pump. Elliptical cylinder concentrating cavities are currently the most commonly used for small solid-state lasers.

4. Optical cavity

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

5. Cooling and filter system

Cooling and filtering systems are essential auxiliary devices for lasers. Solid-state laser produce more severe thermal effects when working, so cooling measures are usually taken. Mainly to cool the laser working substance, pumping 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 high monochromatic laser beam, the filter system plays a large role. Filter system? It can filter most of the pump light and some other interference light, so the output laser is very monochromatic.