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Basic composition and development of laser

Date:

2019-11-28

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1. Basic composition of laser

Although there are many kinds of lasers, they are all produced by excitation and stimulated radiation. Therefore, the basic composition of the laser is fixed, which is composed of three parts: working substance (i.e. working medium which can produce particle number inversion after being excited), excitation source (energy which can make particle number inversion of working substance, also known as pump source) and optical resonator.

① Laser working substance. The generation of laser must choose the right working substance, which can be gas, liquid, solid or semiconductor. In this kind of medium, the inversion of particle number can be realized to make the necessary conditions for obtaining laser. Obviously, the existence of metastable energy levels is very beneficial to the inversion of particle number. There are nearly one thousand kinds of working materials, and the laser wavelength can cover the vacuum ultraviolet band to the far infrared band, which is very wide.

② Incentive sources. In order to reverse the number of particles in the working material, some methods must be used to excite the particle system and increase the number of particles in the high energy level. The method of gas discharge can be used to excite the working substance by using the electron with kinetic energy, which is called electric excitation; the working substance can also be illuminated by pulse light source to generate excitation, which is called light excitation; there are also thermal excitation, chemical excitation, etc. All kinds of excitation methods are called pump or pump. In order to get the laser output continuously, we must pump continuously to maintain the number of particles in the excited state.

③ Optical resonator. With suitable working substance and excitation source, particle number inversion can be realized, but the intensity of stimulated radiation produced by this method is very low, so it can not be applied. So it is thought that an optical resonator can be used to 'amplify' the stimulated radiation. The optical resonator is composed of two mirrors with certain geometry and optical reflection characteristics. Its main functions are as follows.

a. The optical feedback ability is provided to make the stimulated radiation photons go back and forth in the cavity for many times to form coherent continuous oscillation.

b. The direction and frequency of the oscillating laser beam are limited to ensure that the output laser has certain directivity and monochromaticity.

2. Development of laser

Laser is one of the essential core components in modern laser processing system. With the development of laser processing technology, laser is also developing forward, there are many new lasers.

The early laser processing lasers were mainly high-power CO2 gas lasers and lamp pumped solid-state YAG lasers. From the development history of laser processing technology, the first laser is the sealed off CO2 laser in the mid-1970s. Up to now, the fifth generation of C () 2 laser diffusion cooling CO2 laser has appeared. Table 2.2 shows the development status of CO 2 laser.

The early CO2 lasers tend to improve the laser power, but when the laser power reaches certain requirements, the laser beam quality is paid attention to, and the development of the laser is transferred to improve the beam quality. Recently, the diffusion cooled slab CO2 laser, which is close to the diffraction limit, has a good beam quality and has been widely used, especially in the field of laser cutting.


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