In-depth interpretation: 500W single-mode continuous green laser

1. Material vs Laser Wavelength

Since the birth of the first laser in 1960, after more than 60 years of development, laser, as the sharpest and most delicate knife, has been gradually applied in our lives. The combination of laser and biology, medical treatment and diagnosis, and pharmaceutical science has gradually penetrated into daily life in laser treatment, laser surgery, and laser diagnosis. In the field of equipment manufacturing, high-power laser equipment is playing an increasingly important role in cutting, welding, measuring, marking and other links in high-end equipment manufacturing fields such as aviation, aerospace, automobiles, high-speed rail, and ships. In terms of fine micromachining, ultra-short pulse laser has played an irreplaceable role in drilling, scribing, grooving, surface texturing, surface modification, trimming, cleaning and other links in photovoltaic, liquid crystal display, semiconductor, LED, OLED and other fields. effect. With the rapid development of semiconductor pumping technology, near-infrared lasers with a wavelength of 1um have formed a complete industrial chain after years of development, occupying a pivotal position in industrial processing applications. In particular, the 1um near-infrared fiber laser has become the most widely used laser type due to its wide power coverage, excellent beam quality, stability and reliability.

Copper is the third most widely used metal in the world after iron and aluminum. Copper material is one of the most widely used metal materials in modern industrial processing. The terminal demand structure of the copper industry chain covers more than 30 sub-sectors such as aerospace, high-speed trains, intelligent terminal products, electronic communications, and automobiles, and is the main indicator of high-end industrial applications. At present, the large-scale use of infrared fiber lasers in the 1-micron wavelength band has disadvantages such as large spatter and uncontrollable penetration depth in the processing of copper materials due to weak absorption of copper.

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Figure 1 shows the absorption curves of commonly used metal materials for different wavelengths of laser light. It can be seen that the absorption rates of different metals to laser light vary greatly at different wavelengths. Figure 2 shows the comparison curves of absorbance at different wavelengths for metallic copper alone. At room temperature, the absorption rate of copper to near-infrared wavelengths (about 1 micron) is less than 5%, so the efficiency of processing copper materials with infrared light is extremely low, 95% of the laser will be reflected and the laser itself will be damaged; The absorption rate of copper to green wavelengths (515nm and 532nm) is as high as 40%. The selectivity of the material itself to the laser wavelength determines that the most ideal wavelength for precision machining of high-reflection materials is short wavelength (≤700nm)

Figure 1 Comparison of absorption coefficients of different metal materials

Fig. 2 Comparison of the laser absorption rate of metal copper for different three wavelengths

Quoted from "New Progress in Green Laser Processing"

Compared with the short wavelength of ultraviolet laser, the current bottleneck of materials science cannot support the realization of stable high-power ultraviolet laser output. Ultraviolet lasers exceeding 100 watts are extremely rare. On the contrary, through the efforts of scientists from various countries, commercial green lasers have made great progress in recent years. TRUMPF in Germany and IPG in the United States have obtained ultra-high power green light output of more than 3 kilowatts and 1 kilowatt through disc laser technology and fiber laser technology, respectively.

High-power continuous green lasers play an extremely important role in 3D printing and precision welding of copper materials, two important problems in current industrial applications.

2. Application prospects and advantages of high-power green light

At the 14th China International Battery Technology Exhibition in 2021, TRUMPF launched its 3kW high-power continuous green disc laser. The average output power of this product is as high as 3 kilowatts, which represents the strongest power in the current green laser series, and is very suitable for welding of highly reflective materials such as copper and aluminum. Especially in the lithium battery industry represented by new energy vehicle power batteries, TRUMPF green lasers (1000-3000W) can achieve up to 120 layers of copper foil welding with almost no spatter and precise and controllable penetration depth. In addition, high-power green light also has outstanding advantages in 3D printing applications of pure copper materials. At present, the domestic high-power green laser is still blank.

2.1

High reflective metal welding

Due to the outstanding conductivity of copper materials, copper materials are widely used in the lithium battery industry, especially in the power batteries of new energy vehicles. At present, the mainstream still uses high-power infrared fiber lasers for copper welding. Compared with the infrared band, the welding efficiency of copper with green light will be higher, and there is almost no spatter. The splash is fatal to battery processing, and the splash will affect the production safety, performance and life of the battery.

Figure 3 shows the absorption of 1064nm infrared laser by copper. As can be seen from Figure 3, as the melting temperature increases from 0 to 1400K, the absorption of infrared light by copper slowly increases from 5% to about 10%; when copper reaches the melting point (1400K), copper The absorption rate of infrared band laser will increase from 10% to about 17% in steps, and then the absorption rate will increase slowly as the temperature continues to increase. This sudden change in absorption before and after the melting point can cause some of the molten material to escape as a splash, and it can also cause the small holes to collapse, forcing the entire process to start all over again. Especially in the post-process welding of lithium batteries, the yield of welding has a direct impact on the cost of the battery.

Figure 4 presents the absorption curves of copper for different wavelengths (infrared, green and blue) at different temperatures. The green lines in the figure represent the absorption rates of green light by copper at 20°C (solid state) and 1600°C (melted state), respectively. At room temperature of 20 °C, when copper is in a solid state, the absorption rate of the green light band is about 40%, and when the temperature rises to 1600 °C and the copper is in a molten state, the absorption rate drops by about 5%. That is, the absorption of green light decreases slightly after copper is melted. This feature helps to obtain stable small holes when machining copper, and can achieve almost zero spatter. This is a clear advantage of green lasers over infrared laser welding.

Copper materials are widely used in high-end manufacturing due to their excellent thermal conductivity and electrical conductivity. For example, in the fields of aerospace, high-speed trains, and the automotive industry, there is a direct application demand for 3D printing technology of pure copper materials.

The laser light source for 3D printing of metal materials currently mainly uses a 1um near-infrared single-mode fiber laser. The 1um near-infrared single-mode fiber laser has the disadvantage that the absorption coefficient of copper material is low, and it has a large influence with temperature, resulting in low density of printed samples and poor process robustness. Green laser, as the best light source for 3D printing of highly reflective metal materials, 3D printing pure copper materials can well solve related problems and achieve a density greater than 99.95%.

3. High-power continuous single-mode green light of the laser

RFH Laser Co., Ltd. is mainly engaged in the R&D, production and sales of "advanced short-wavelength fiber lasers" and "laser precision machining solutions". Scheme of the Laser Company

4. Committed to the advanced application of short-wavelength high-power lasers

The continuous single-mode green laser has good output power stability, excellent beam quality, and high absorption rate for highly reflective materials, especially copper, making it promising for 3D printing of pure copper materials. By further adding a spatial modulator, pulsed green light with a high-speed modulation frequency can also be obtained, which makes it also promising for precision cutting and welding of highly reflective materials.

The continuous single-mode green laser uses free space output, which is beneficial to ensure excellent beam quality. The laser can also provide a flexible transmission method coupled to the optical fiber, which is more convenient to match the automatic control, and is applied to the welding process of high-reflection materials. After a long-term exploration of the laser welding process, it has been shown that better welding results can be obtained by using output spots (beam shaping) with different energy distributions. In addition, the laser-based single-module single-mode green laser can also perform multi-module space or fiber bundling. On the one hand, green light output with flexible beam energy distribution can be obtained; on the other hand, continuous fiber green light output of several kilowatts or even tens of thousands of watts can be obtained, providing core high-quality, high-efficiency and high-yield laser welding. Power short wavelength light source.

The continuous high-power green laser can provide an effective solution for the processing and application of copper materials, and is expected to shine in pure copper 3D printing and high-reflection metal precision welding.