Mar 21, 2020
The principle of laser
The laser consists of a pump source, a gain medium with a metastable energy level, and a resonator. Taking the semiconductor pumped fiber laser as an example, the specific process of laser generation can be divided into the following five steps in detail:
In the first step, the pump light is introduced, and the semiconductor laser, as the pump source of the laser, emits the pump light with a certain linewidth and enters the fiber after passing through the beam combiner;
In the second step, the gain medium is energized, and the gain fiber absorbs the pump light of a specific wavelength, which makes the energy level transition of the particle up to metastable state;
In the third step, photons are formed by spontaneous emission, and the metastable state particles spontaneously transition downward to release energy, producing photons with different directions and phases;
The fourth step is to realize optical amplification by stimulated radiation. Photons moving along the axis can move back and forth between mirrors (gratings) (photons not running along the axis quickly escape), and photons can generate homogeneous photons when they encounter high-energy (metastable) particles in the gain medium, so as to achieve optical amplification effect;
The fifth step, laser output, after reaching certain requirements to achieve continuous or pulse form of laser output.
There are four common classifications of lasers: gain medium, output power, operation mode, and pulse width.
According to the gain medium: the gain medium of laser includes gas, liquid, and solid. The specific gain medium determines the laser wavelength, output power, and application field. CO2 gas laser is representative in gas, ruby laser, semiconductor laser, fiber laser, and YAG laser are representative in solid.
According to the output power: it can be divided into small power (0-100w), medium power (100-1kw), and high power (above 1kW); but sometimes it is defined as medium power within the range of 100-1.5kw. Different laser power adapts to different application scenarios.
According to working mode: it can be divided into continuous laser and pulse laser. The CW laser can output continuously for a long period of time, with stable operation and high thermal effect. Pulse laser is output in the form of a pulse, which is characterized by high peak power and small thermal effect. According to the length of pulse time, pulse laser can be further divided into milliseconds, microseconds, nanoseconds, picoseconds and femtoseconds. Generally speaking, the shorter the pulse time, the higher the single pulse energy, the narrower the pulse width, and the higher the processing accuracy.
According to the output wavelength: it can be divided into the infrared laser, visible laser, UV laser, etc. Different structures of materials can absorb different wavelength range, for example, metal has higher near-infrared absorption.
Fiber laser has outstanding advantages in material processing
Fiber laser promotes the development of laser processing methods in breadth and depth. In the traditional field, high-power laser promotes the penetration of laser equipment into the cutting, welding, marking, and other links of high-end equipment such as aerospace, transportation, etc. In the emerging field, fiber laser broadens the depth of laser processing and forms an incremental market, mainly including precision processing in consumer electronics, photovoltaic, lithium battery, semiconductor, and other fields.
From the technical point of view, fiber laser is superior to other lasers. The technical advantages of fiber laser for processing are: 1) good beam quality, easy to achieve high power. 2) The large surface area of optical fiber, good heat dissipation. 3) The optical path is completely closed, with good stability, long service life, and less maintenance. 4) Small size, flexible transmission. 5) The wavelength is in the range of 700nm-2000nm, which is more applicable in the field of material processing.
From the perspective of cost, fiber laser has a very high-cost performance advantage. Take CO2 laser as a comparison:
1) Because of the high beam quality and the high material absorption rate, the processing speed of fiber laser is faster. Taking the cutting of thin plate as an example, the cutting speed of fiber laser can reach 2-3 times of that of CO2 laser with the same power;
2) The electro-optical conversion rate of fiber laser is over 30% and the power consumption is low. The CO2 laser's optical path depends on the reflector completely. The optical path decays quickly and the energy loss is more. The electro-optical conversion rate is below 10%;
3) The structure of fiber laser is simple and stable, the external optical path is maintenance-free, the average time between failures is more than 100000 hours, and there is basically no consumables. The structure of the CO2 laser system is complex, the reflector and resonator need regular maintenance, turbine bearing replacement cost is expensive and maintenance cost is high.
Comparing the main performance parameters of kilowatt industrial laser on the market, compared with other lasers, fiber laser has the advantages of good output laser beam quality, high energy density, high electro-optical efficiency, easy to use, a wide range of Machinable materials, low comprehensive operation cost, etc., so it is widely used in carving/marking, cutting/drilling, etc, cladding/welding, surface treatment, rapid prototyping, and other materials processing and optical communication fields, known as the "third-generation laser", have broad application prospects.
The laser is located in the center of the laser industry chain, and China has become the largest and fastest-growing laser market in the world. The laser is the core optical component of the terminal laser equipment, which is located in the central position of the whole industrial chain. At the same time, from the cost point of view, the laser cost accounts for about 30% - 50% of the total cost of the equipment, which is the most valuable core component of the laser equipment.