A conventional fiber laser cutter laser consists of three parts: working material, pump source and optical resonator.
1.Working substance
Working material is the material basis of laser generation, the core part of laser, and the material system used to realize particle number inversion and generate stimulated radiation.
There are two ways to classify working materials: one is based on the existing form of working materials, which can be divided into gas, solid, liquid and semiconductor; The other is to analyze the energy level structure applicable to the process of generating laser according to the rate equation theory, which can be divided into three-level system and four-level system.
The particles that produce the fiber laser cutting machine laser in the gas laser are gas molecules or atoms. In the solid laser, crystals or glasses doped with a small amount of transition metal ions or rare earth ions are the working materials, and doped ions are the working particles. After the particle number inversion generated by the external energy pump, stimulated radiation can be generated. The crystals and glasses are the matrix materials.
The working substance of liquid laser is liquid. The common one is dye laser. Its working substance is the solution composed of dye dissolved in dry solvent. The dye molecule is the working particle, and the solvent is equivalent to the matrix. The working material of the semiconductor laser is semiconductor. Although the semiconductor is solid, the formation mechanism of the particle number inversion of the semiconductor laser is fundamentally different from that of the ordinary homogeneous laser, so the two are not generally classified.
2.Pump
It is a device that provides energy for the inversion of particle number. According to the energy form used in the excitation, the pumping modes include discharge excitation, light excitation, thermal energy excitation, chemical energy excitation, etc.
Gas discharge excitation is a commonly used excitation method for gas lasers. Its excitation mechanism is to use gas molecules to ionize and conduct electricity under high voltage. At the same time, gas molecules (or atoms, ions) collide with electrons accelerated by the electric field, absorb the energy of electrons, and then jump to the high energy level, forming the inversion of particle number; In addition, the sonic electrons generated by the electron gun can also be used to pump the working material, and the transition to the sound level is called electron beam excitation; The semiconductor laser is pumped by injection current, which is called injection pump.
Light excitation is the use of light to irradiate the working material, and the working material of the fiber laser cutting machine absorbs the light energy to produce particle number inversion. The light source excited by light can be high-efficiency and high-intensity light emitting lamp, solar energy or laser. Solid state lasers and liquid lasers are usually excited by light.
Thermal energy excitation is to increase the number of gas particles on the high energy level by means of high temperature heating, and then suddenly reduce the gas temperature, because the thermal relaxation time of high and low energy levels is different, the relaxation time of low energy level is short, and the relaxation time of high energy level is long, so as to realize the inversion of particle number between high and low energy levels.
Chemical energy excitation uses the chemical energy released in the chemical reaction process to pump particles to the upper energy level and establish the inversion of particle number. Unlike the aforementioned discharge excitation, chemical excitation and thermal excitation require external energy when working. Therefore, in some special places where there is a lack of power supply, chemical laser can play its advantages of fiber laser cutting machine.
3.Optical cavity Optical cavity (optical cavity for short)
It is the external condition for laser generation and an important part of laser. The simplest optical resonator is activated
Two mirrors coated with high reflectivity materials are properly placed at both ends of the medium. With the characteristics of high directivity, high monochromaticity, high coherence and high brightness, the fiber laser cutting machine is inseparable from the optical resonator.
The optical resonator has the dual functions of positive feedback and mode selection. The so-called positive feedback means that the initial light intensity travels back and forth between the mirrors, and the equivalent dry increases the length of the active medium, which can ultimately ensure a certain size of light intensity. The so-called mode selection is to control the characteristics of the oscillating beam in the cavity, so that the oscillation of the fiber laser cutter established in the cavity is limited to a few eigenmodes determined by the cavity, so as to increase the number of photons in a single mode, and obtain strong coherent light with good monochromaticity and good directionality.
Laser is a kind of electromagnetic wave. The optical resonator of laser beam confines the electromagnetic wave in a limited range of space. According to Maxwell’s electromagnetic field theory, there can only be a series of split eigenstates of electric shock wave in a certain range of space. These eigenstates are the modes of optical resonator. The laser mode is also the eigenstates of electric shock wave that can be distinguished in the optical cavity, which is determined by the structure of the cavity.
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