1. Laser Technology Background

Since its birth in the mid-20th century, laser technology has become one of the cornerstones of modern science and technology, and its development background is rich and far-reaching. In 1960, the advent of the first laser marked the beginning of a new era. Maiman successfully produced coherent light using ruby crystals. This new light source has unprecedented monochromaticity, coherence and directionality, opening up new horizons for scientific research and technological applications. After entering the 21st century, with the development of semiconductor pumping technology, fiber laser technology and ultrafast laser technology, laser technology has ushered in a new leap. Semiconductor pumping technology improves the electro-optical conversion efficiency of lasers and reduces manufacturing costs. Fiber lasers have become the preferred choice for industrial processing with their high power, high stability and compact structural design. Ultrafast lasers, with their ultrashort pulse characteristics, have shown great potential in micro-nano processing and biomedical fields. At present, laser technology is developing towards higher power, higher precision and wider application.

With the rapid development of fiber laser technology, the output power, beam quality and electro-optical efficiency of lasers have been continuously improved, providing a technical basis for the research and development of high-power green lasers. The development of nonlinear optical frequency doubling technology has made it possible to switch from infrared fiber lasers to green lasers, increasing the output power of green lasers. In the field of industrial processing, high-power laser equipment plays an important role in cutting, welding, marking, and measuring in the fields of aerospace, automobile manufacturing, and shipbuilding; in the field of medical applications, the precision and controllability of lasers make them widely used in ophthalmic surgery, skin treatment, and other medical procedures. Laser technology has penetrated into all aspects of daily life, from industrial manufacturing to artistic creation to scientific research. With the advancement of technology, the research and development of high-power lasers has significantly improved the industrial processing capabilities of lasers.

2. Application development and advantages of high-power, short-wavelength lasers

The development of high-power green lasers has attracted much attention. Due to its continuous operation mode and waveguide structure, continuous fiber lasers have the advantages of uniform output laser energy, high gain, high conversion efficiency, ultra-high power output, good beam quality, easy single-mode output and stable performance.

The principle of interaction between laser and material is complex and diverse. Different laser parameters (such as wavelength, power, pulse width, etc.) and material properties will lead to different interaction effects. The results of these interactions are widely used in the application of laser technology, such as material processing, medical treatment, scientific research, etc.

Copper material is one of the most widely used metal materials in the world. Under normal temperature conditions, as shown in Figure 1, the absorption rate of copper for lasers in the 1064nm band is less than 5%, while the absorption rate of 532nm green light can reach 40%, which is equivalent to 8 times that of near-infrared band lasers. Copper is widely used in lithium battery, microelectronics and other industries. Currently, the most commonly used near-infrared laser in the industry is the 1064nm band. Since copper has a low absorption rate for 1064nm band lasers, problems such as low efficiency, bubbles, and spatter will occur during processing. Green lasers are used in cutting, welding, and additive manufacturing of high-reflective materials such as copper, which has obvious advantages over near-infrared lasers. Therefore, achieving high-power, high-efficiency continuous green light output has become one of the research hotspots of lasers.

Figure 1. Absorption rate of copper at different wavelengths, cited from "Research Progress of High-Power Continuous Green Lasers"

Figure 2 shows the absorption rate curves of several typical powder materials for lasers of different wavelengths. It can be seen that different materials have different absorption rate curves for lasers of different wavelengths. The laser energy absorbed by the material during the processing can be converted into heat energy, causing the local temperature of the material to rise. This thermal effect is very important in processes such as laser cutting, welding and heat treatment, causing phase changes in the material, such as melting, evaporation or sublimation.

Figure 2. Absorption rate of typical powder materials for lasers of different wavelengths

An important application of green laser is 3D printing technology. In the field of metal 3D printing, green laser can improve printing quality and realize 3D printing of complex structures of pure copper materials. Figure 3 shows the analysis results of pure copper printing by single-mode continuous green fiber laser. The equipment integrator is Xihe Additive, which uses the 500W single-mode green laser launched by Gongda Laser as the printing light source.

Figure 3. Single-mode continuous green fiber laser printing pure copper (Xihe Additive) (density ≥ 99.5%)

The use of single-mode continuous green fiber lasers as a light source for printing pure copper is a relatively new technology that takes advantage of the beam characteristics of green lasers to overcome the challenges of traditional laser technology in processing highly reflective materials. Since pure copper absorbs green light much more than near-infrared light, green lasers are more effective in processing copper materials. On the other hand, the beam produced by a single-mode laser has high quality and consistency, which is critical for precision processing, especially when printing pure copper, to ensure the fineness and consistency of the printing process.

Figure 4. Pure copper heat treatment sensor printed by Xihe Additive XH-M160G 3D printing

Figure 5. Pure copper motor windings printed by Xihe Additive XH-M160G 3D printing

In the development of short-wavelength lasers, ultraviolet (UV) lasers and blue lasers have attracted much attention due to their unique application characteristics. Due to the short wavelength of ultraviolet lasers, the purity and optical properties of materials are extremely high. It is currently difficult to find materials that can withstand high-power ultraviolet lasers, and ultraviolet lasers exceeding 100 watts are rare on the market. Although blue laser manufacturers have achieved kilowatt-level power output, blue lasers need to be spatially combined before fiber beam combining. This process has strict requirements on the quality, stability and power distribution of the laser beam. Compared with fiber lasers, the beam quality of blue lasers is poor, which limits its performance in certain precision machining applications.

On the other hand, through the efforts of researchers from various countries, commercial green lasers have made great progress in recent years. In 2021, TRUMPF Group of Germany launched the high-power continuous green laser disc laser TruDisk 3022, which can provide a maximum output power of 3kW in multi-mode, the highest power in the current green laser series, demonstrating its application advantages in copper welding, but its price is very expensive. In 2022, IPG of the United States launched the world's first kilowatt-class single-mode nanosecond pulsed green laser GLPN-1000, which can provide an average power of up to 1kW. The whole machine is compact in size and has an electro-optical conversion efficiency of up to 25%, which has attracted widespread attention in the industry.

3. The world's first nearly single-mode 2-kilowatt continuous green laser

According to the latest report from market research firm Optech Consulting, the global market size of materials processing laser systems is estimated to be US$23.5 billion in 2023, a year-on-year increase of 4%. With the development of high-end manufacturing, the demand for high-power green lasers continues to grow.

Shenzhen Gongda Laser, mainly engaged in the research and development, production and sales of "advanced short-wavelength fiber lasers" and "laser precision processing solutions", is a laser company focusing on the research and development, production and application solutions of medium and high power short-wavelength (green and ultraviolet) all-fiber lasers. Following the launch of the 500W single-mode green laser in 2022 and the 1000W single-mode and 3000W multi-mode continuous green lasers in 2023, Gongda Laser has launched a new 2-kilowatt near-single-mode green fiber laser with a maximum output power of 2 kilowatts, which has been tested and verified by terminal-related industry customers. Gongda Laser is the world's first manufacturer that can provide 2-kilowatt near-single-mode continuous green laser products.

Figure 6. Nearly single-mode 2 kW continuous green laser product

The main laser characteristics and test results are as follows:

(1) Basic parameters of laser Table 1. Basic parameters of laser

(2) Power stability: after continuous light copying for 12 hours, the power fluctuation of the whole machine is less than 1.5%

Figure 7. 12-hour power stability test curve

(3) Spot energy distribution test

Figure 8. Spot energy distribution test diagram

(4) Beam quality test

Figure 9. Beam quality test @ 2 kW

4. Conclusion and Outlook

Gongda Laser's latest near-single-mode 2-kilowatt continuous green laser is the world's highest average power quasi-single-mode continuous fiber green laser. The launch of this product provides more sufficient energy for the processing of high-reflective materials. The near-single-mode output ensures the high quality and consistency of the laser beam, which is expected to bring higher welding quality, higher efficiency and deeper penetration to thick copper processing. The structure of all-fiber fundamental frequency and extra-cavity frequency doubling provides high stability and reliability, while ensuring the compactness and easy integration of the laser. With the continuous advancement of technology and the continuous maturity of the market, we have reason to believe that high-power fiber green lasers will bring more possibilities to society.

High-power green light has obvious advantages in precision welding of copper materials, especially in the welding of electrically controlled IGBTs and flat wire motors, with small thermal impact, small spatter, stable tension and high yield. Test data of 2-kilowatt near-single-mode green light for motor welding.

In addition to having outstanding physical property advantages in welding high-reflective metal materials such as copper, high-power fiber green lasers also have great application potential in high-precision and high-efficiency copper material 3D printing.

In the future, we at Gongda Laser will continue to work hard to develop more innovative technologies, further improve the power, efficiency and reliability of lasers, while reducing costs, matching more important application scenarios, and contributing to the upgrading of global high-end manufacturing.