What is the principle of laser?

Except for free electron lasers, the basic working principles of various lasers are the same. The necessary condition for generating laser is that the number of particles is reversed, and the gain is greater than the loss, so the necessary components of the device are excitation (or pumping) source and working medium with metastable energy level. Excitation means that the working medium is excited to the excited state after absorbing external energy, which creates conditions for realizing and maintaining the inversion of particle number. There are light excitation, electric excitation, chemical excitation and nuclear energy excitation. The metastable energy level of the working medium makes stimulated radiation dominant, thus realizing optical amplification. The common part of a laser is a resonator, but the resonator (see optical resonator) is not an essential part. The resonant cavity can make the photons in the cavity have the same frequency, phase and running direction, thus making the laser have good directivity and coherence. But also can shorten the length of the working substance, and adjust the mode of the generated laser by changing the length of the resonant cavity, so general lasers have resonant cavities. Laser working substance refers to the substance system used to realize population inversion and generate stimulated radiation amplification of light, sometimes called laser gain medium, which can be solid (crystal, glass), gas (atomic gas, ionic gas, molecular gas), semiconductor and liquid. The main requirements for laser working materials are to achieve a large degree of particle number inversion between the specific energy levels of their working particles as much as possible, and to maintain this inversion as effectively as possible during the whole laser emission process; Therefore, the working fluid is required to have appropriate energy level structure and transition characteristics. Excitation pumping system refers to the mechanism or device that provides energy for the laser working substance to realize and maintain the inversion of particle number. According to different working substances and laser working conditions, different excitation methods and devices can be used, and the following four are common. ① Optical excitation (optical pump). The working substance is irradiated by light from an external light source to realize the inversion of the number of particles. The whole excitation device usually consists of gas discharge light source (such as xenon lamp and krypton lamp) and condenser. This excitation method is also called lamp pumping. ② Gas discharge excitation. The number of particles is reversed by using the gas discharge process in the gas working substance. The whole excitation device usually consists of a discharge electrode and a discharge power supply. ③ Chemical stimulation. The inversion of particle number is realized by using the chemical reaction process in the working medium, which usually requires suitable chemical reactants and corresponding initiation measures. (4) Nuclear energy incentives. It uses fission fragments, high-energy particles or radiation produced by small-scale nuclear fission reaction to excite the working medium and realize the inversion of particle number. An optical resonant cavity usually consists of two mirrors with a certain geometric shape and optical reflection characteristics in a specific way. The functions are as follows: ① Providing optical feedback ability, making stimulated radiation photons go back and forth in the cavity many times, forming coherent continuous oscillation. ② Restrict the direction and frequency of the oscillating beam in the cavity to ensure that the output laser has certain directivity and monochromaticity. * * * The cavity function ① is determined by the geometric shape (mirror curvature radius) and the relative combination mode of the two mirrors that usually constitute the cavity; Effect (2) is determined by the fact that a given cavity type has different selective loss characteristics for light with different propagation directions and frequencies in the cavity. Classified, there are many kinds of lasers. Next, the working substance, excitation mode, working mode and output wavelength range of the laser will be introduced respectively. For more information, please consult Chongqing Qifeng Laser Equipment Co., Ltd., thank you!