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Fiber laser refers to a laser that uses rare earth element-doped glass fiber as a gain medium. Fiber laser can be developed on the basis of fiber amplifier: under the action of pump light, it is easy to form high power density in the fiber, resulting in the laser working substance of the laser. The energy level is "number inversion", and the laser oscillation output can be formed when a positive feedback loop (constituting a resonant cavity) is properly added. The processing requirements are becoming more and more diverse and demanding. The laser, the heart of the laser cutting machine, also has a distinction between single-mode and multi-mode. Fiber lasers have a wide range of applications, including laser fiber optic communication, laser space telecommunication, industrial shipbuilding, automobile manufacturing, laser engraving, laser marking, laser cutting, printing rolls, metal and non-metal drilling, cutting, welding, military defense and security, Medical equipment, large infrastructure, as a pump source for other lasers, etc.
It is well known that the energy distribution of the beam excited by the fiber laser is similar to the "Gaussian distribution". The principle and structure of the fiber laser are composed of a pump source, a multimode coupler (beam combiner), a fiber grating, an active fiber, and a beam calibration output module. And passive fiber (energy output fiber) and other components. When there is only one pump module inside the laser, it is called a single-mode laser, and multiple pump modules are combined together to allow multiple pump beams to enter the active fiber through a beam combiner, so that higher power can be obtained. The laser beam of this multi-module combination is a multi-mode laser. Therefore, among the mainstream fiber laser products, single-mode lasers are mostly medium and small power, while high-power products are mostly multi-mode lasers.
The difference between multi-mode and single-mode: the core of single-mode is relatively thin, and it emits a typical Gaussian beam with very concentrated energy, similar to a steep mountain, and the beam quality is better than that of multi-mode; multi-mode is equivalent to multiple Gaussian beams The combination of, so the energy distribution is similar to an inverted cup, which is relatively average, of course, the beam quality is worse than that of single mode. According to different characteristics, the application directions of single-mode and multi-mode are also different. For example, in the cutting of stainless steel/carbon steel sheets of 1mm and below, the processing efficiency of single-mode is significantly better than that of multi-mode (single-mode is 15% faster~ 20%), and the cutting quality is similar; in the thick plate cutting of 2mm and above, the high-power multi-mode laser performs better in both quality and efficiency.
From the point of view of power level, lasers within 1000W are mainly processed with thin plates due to their low energy. Therefore, single-mode configuration of lasers within 1KW is more in line with the actual market conditions, and lasers with power above 1KW should be thin and thick. From the perspective of the entire processing industry, the improvement of processing quality is a rigid requirement that cannot be compromised. Therefore, many high-power lasers do not consider single-mode in the selection. At the same time, the single-mode fiber core is generally thinner, which means that the same power laser is transmitted in it, and the single-mode fiber core has a larger light energy load, which is a test for the material. At the same time, when cutting highly reflective materials, the high-intensity reflected light and the emitted laser are superimposed. If the tolerance of the fiber material is insufficient, it will be very easy to "burn the fiber core", and it is also a challenge to the life of the core material! Therefore, many laser manufacturers are in high The configuration of the power fiber laser still chooses the multi-mode configuration!
