What Are The Characteristics Of High-power Fiber Lasers?

High-Power Fiber Lasers have also shown great application potential in energy exploration, large scientific devices, space science, environmental science and other fields, and will become a powerful tool for human beings to understand and transform the world.

The advantages of high-power fiber lasers are as follows.

(1) The beam quality is good. The waveguide structure of the fiber determines that the fiber laser is easy to obtain a single transverse mode output, and is less affected by external factors, and can achieve high-brightness laser output.

(2) High efficiency. Fiber lasers can achieve high light-to-light conversion efficiency by selecting a semiconductor laser that matches the emission wavelength and the absorption characteristics of doped rare earth elements as the pump source. For ytterbium-doped high-power fiber lasers, semiconductor lasers of 915 nm or 975 nm are generally selected. Due to the simple energy level structure of Yb3+, phenomena such as up-conversion, excited state absorption, and concentration quenching rarely occur, and the fluorescence lifetime is long. Energy can be effectively stored to achieve high-power operation. The overall electro-optic efficiency of commercial fiber lasers is as high as 25%, which is conducive to reducing costs, energy saving and environmental protection.

(3) Good heat dissipation characteristics. Fiber lasers use elongated rare-earth element-doped fibers as laser gain media, which have a very large surface area to volume ratio. It is about 1000 times that of a solid block laser, and has a natural advantage in heat dissipation. In the case of medium and low power, no special cooling of the optical fiber is required. In the case of high power, water cooling is used to dissipate heat, which can also effectively avoid the degradation of beam quality and efficiency caused by thermal effects in solid-state lasers.

(4) Compact structure and high reliability. Since the fiber laser uses a small and soft fiber as the laser gain medium, it is beneficial to compress the volume and save the cost. The pump source also uses a semiconductor laser that is small in size and easy to be modularized. Commercial products can generally be output with pigtails. Combined with fiber-optic devices such as fiber Bragg gratings, all these devices can be fully optical-fiberized as long as they are fused with each other. They have high immunity to environmental disturbances and high stability, which can save maintenance time and costs.

Typical Applications of High Power Fiber Lasers

Due to the advantages of good beam quality, high electro-optical efficiency, compact structure, and good reliability, fiber lasers have excellent performance in all aspects of industrial processing, medical treatment, remote sensing, security, scientific research and other fields.

In the industrial field, fiber lasers can be divided into three levels according to output power: low-power fiber lasers (<50 watts), mainly used in microstructure processing, laser marking, resistance adjustment, precision drilling, metal engraving, etc.; medium-power fiber lasers (50-500 watts), mainly used in drilling, welding, cutting and surface treatment of thin metal plates; high-power fiber lasers (>1000 watts), mainly used in cutting thick metal plates, metal surface coating, three-dimensional processing of special plates, etc. The flexible feature of the optical fiber can be well combined with the robot arm to meet the application requirements of various complex industrial environments. The 3D printing technology that has emerged in recent years especially requires this kind of high-brightness laser system.

In the medical field, the ideal laser wavelength is 1.3 microns, which can be used for diagnostic imaging; between 1.5 microns (absorption peak of water) and 4 microns can be used for surgery. For medical applications, the biggest advantage of fiber lasers is their compact, bendable geometry. A short coherent wavelength light source with a wide spectral range and high output power is the key to obtain a high-speed, ultra-high-resolution optical coherence tomography system. Erbium-doped fiber lasers and ytterbium-doped Raman fiber lasers have the typical requirements for optical coherence tomography: small and compact, robust, affordable, relatively high power, and high resolution without optical alignment. High-power Erbium-doped fiber lasers and Thulium-doped fiber lasers are well suited for medical and surgical applications. The researchers found that the laser can not only quickly cut and coagulate soft tissue, but also has hemostatic function in the wavelength of 1.94 microns. And thanks to the excellent beam quality of fiber lasers, the surgery is performed with high precision.

In the field of remote sensing, the output wavelength of mid-infrared fiber lasers such as erbium-doped fiber lasers and thulium-doped fiber lasers is located in the atmospheric window, which can pass through the atmosphere with low loss. In particular, thulium-doped fiber lasers are easier to obtain high power output in the eye-safe band, and have more advantages in power amplification. Another advantage of fiber lasers is that they are compact and portable, which will help reduce the load on aviation or aerospace vehicles.

In the field of national defense and military affairs, lasers are widely used in radar detection, secure communication, guidance, and killing. Since the birth of the fiber laser, it has become a popular candidate light source for the new generation of laser weapons due to its unique advantages. The high beam quality of the fiber laser is especially suitable for long-distance transmission of energy seedlings. Compared with other light sources, its smaller size is conducive to the high mobility of the launch platform and improves the adaptability and survivability on the battlefield. On the battlefield in Afghanistan, SPATA's "Zeus" laser mine-sweeping system has performed mine-sweeping tasks. Since 2009, the U.S. Navy has repeatedly used fiber laser systems to destroy unmanned aerial vehicles, artillery shells, and small ships, and it has been installed on warships in 2014. In 2012, Rheinmetall, a German defense arms dealer, launched a dual-tube laser system with an output power of 50 kilowatts, which intercepted and destroyed targets such as drones and artillery shells in demonstration experiments.

Laser Weapon

Laser weapon is a kind of new concept weapon which is developing rapidly. Laser weapons emit high-energy laser light to the target surface at the speed of light, and damage the key devices such as photoelectric detection, navigation and guidance, or make the target "blind, blind", or burn through the shell of the vehicle to shoot it down, or detonate the fuel to make it explode in the air, and the damage task can be completed in a short time. Since the birth of laser weapons, its development has experienced many ups and downs. The maturity of solid-state laser technologies such as fiber lasers has injected new impetus into the development of laser weapons and has become the research focus of major military powers. At present, the United States, the United Kingdom, Russia, Germany, India and other countries have all launched the development of laser weapons and carried out related tests. It is just around the corner that laser weapons will enter the battlefield.

Fiber laser technology represents the development direction of high power and high brightness laser. It organically integrates waveguide fiber technology and semiconductor laser pumping technology. The high-power fiber laser with optical fiber as the carrier is expected to meet the urgent demand for high-power and high-efficiency lasers in the fields of advanced laser manufacturing and military defense in the future. It is a cutting-edge technology with important strategic significance for the national economy and national security. High-power fiber lasers have also shown great application potential in energy exploration, large scientific devices, space science, environmental science and other fields, and will become a powerful tool for human beings to understand and transform the world.

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