American TeraDiode has developed an ultra-high brightness kilowatt-level direct semiconductor laser. The laser uses a new beam combining and shaping technology based on the COTS semiconductor laser, so that the beam parametric product of the output beam reaches 3.75mm-mrad, which is the lowest value in the kilowatt-level direct semiconductor laser reported so far. . When a single fiber with a core diameter of 50 μm and a numerical aperture of 0.15 is used for coupling out, the output power of the laser reaches 2030 W at a single center wavelength. This two-kilowatt direct semiconductor laser with pigtail output has a brightness comparable to that of industrial fiber and CO2 lasers, and its output beam brightness is more than ten times higher than the best direct semiconductor lasers today. It is suitable for industrial material processing, including Cutting and welding of sheet metal.
1 Introduction
Direct semiconductor laser has the characteristics of high efficiency, compact arrangement, wide wavelength range, low cost and high reliability. These advantages are very attractive to other lasers. However, the quality of the output beam of the direct semiconductor laser is problematic, so its scope of application is limited. It is mainly used as a pump source for lasers, including large-volume solid-state lasers (rod or disk lasers) and fiber lasers. In other words, they are mainly used as brightness converters. Therefore, the high-brightness industrial lasers currently used in cutting and welding are mainly carbon dioxide, optical fiber and large-volume solid-state lasers.
For the first time, TeraDiode has developed a direct semiconductor laser that uses revolutionary beam shaping technology to bring the output power and beam quality to the requirements of industrial-grade lasers. This technology can enable the laser to reach an output power of tens of kilowatts while maintaining a high beam quality. Using this laser to cut metal of standard thickness, the cutting quality can be comparable to the lasers currently used in industry.
Kilowatt-level direct semiconductor lasers have broad market potential. In industry, industrial processing processes such as sheet metal cutting and bolt hole welding require sufficient laser brightness. High-performance fiber and solid-state lasers require narrow linewidth ultra-high brightness lasers as pump sources, and their linewidth should be less than 4 nm. The application of directed energy weapons requires very high laser power, which requires the beam to reach an output power of more than 10 kilowatts when it is close to the diffraction limit. Traditional direct semiconductor lasers are cheap and highly reliable. However, it lacks sufficient brightness when implementing special material processing or pump-related applications. And this high-power and high-brightness pigtail output direct semiconductor laser provides superior efficiency, price and reliability, and its characteristics are suitable for industrial and military applications.
Semiconductor lasers are the most efficient lasers, but data shows that their spatial brightness is generally lower than other industrial kilowatt-level lasers. These kilowatt-level lasers include carbon dioxide, fiber optics, bulk solids and disk lasers. For example, in the cutting and welding of metal sheets, lasers with a beam parametric product (BPP) range of 3 to 10 mm-mrad are often used. In the kilowatt-level laser, this pigtail output laser has a significantly higher BPP value. Although the inherent spatial brightness of semiconductor lasers is low, significant developments have been made in recent years. Using rough wavelength division multiplexing technology, the BPP range of the kilowatt-level semiconductor laser can be within 20mm-mrad (equivalent to an output fiber with a core diameter of 400μm and a numerical aperture of 0.1). However, in high-brightness industrial applications, its BPP still needs to be significantly improved.
TeraDiode has developed an ultra-high brightness pigtail output semiconductor laser, which uses a new type of beam combining and shaping technology. This pigtail output direct semiconductor laser can transmit a single wavelength beam with an optical power of 2040W from a fiber with a core diameter of 50μm, and the output fiber numerical aperture is 0.18 (including 90% power). The BPP of this laser is 3.75mm-mrad, which is much lower than that of other existing direct-fiber output direct semiconductor lasers. Therefore, the center wavelength of the laser is stable over the entire power range.
2. Technical methods
TeraDiode has developed a pigtail output semiconductor laser. The laser uses optical wave combining technology (WBC) to obtain brightness that is several orders of magnitude higher than existing commercial lasers. The outer cavity of WBC is used for two purposes: 1) to stabilize the center wavelength; 2) to increase the brightness. A semiconductor laser array is placed in the external cavity, which consists of a conversion lens, a diffraction grating, and an output coupler (see Figure 7). The wavelength of the light emitted by any of the three lasers in the figure is fixed, as shown in the three colors of red, green, and blue. The brightness enhancement feature is represented by two black beams in the figure, which represent the spatial superposition of three basic beams on the output coupler. The output beam quality is almost the same as the single basic output beam quality in the array. If the optical power of each basic beam is kept constant, when the number of basic beams is known, the total output power can be obtained.
TeraDiode uses passively cooled semiconductor laser bars for all commercial products. This passively cooled semiconductor laser bar is very reliable, with a lifespan of more than 20,000 hours and an average time to failure of more than 100,000 hours. These laser bars can be cooled with standard industrial coolant, and the coolant does not require current control. All high-brightness direct semiconductor lasers mentioned in the paper use this passively cooled semiconductor laser bar.
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