Early fiber lasers were low in efficiency and power, and limited, until a more effective method of delivering the pump beam to the cladding appeared.
This is a method that can overcome the limitations of previous launch methods-the side-pump beam method helps unleash the true potential of fiber lasers, opens a new era of high-power fiber lasers and amplifiers, and completely changes the development of fiber technology. Further development has promoted the large-scale adoption of fiber lasers in different application fields such as industry, science, and medical equipment. The development of industrial fiber lasers can be divided into two stages, which are characterized by power combiners and brightness converters.
The power combiner in the first stage contains multiple laser diode pump packages, designed to effectively combine their multimode light into passive transmission fibers. The use of redundant single-emitter diode packaging can ensure the high reliability of the laser. There are two fiber Bragg grating mirrors in the optical cavity of the laser, located in the central single-mode core, which is a high-purity fiber with a cladding doped with various rare earth elements.
This optical cavity converts low-quality diode light into a single-mode laser beam. One of the fiber Bragg gratings serves as a total reflector, and the other serves as a partial reflector or output coupler. No other elements are doped in the multi-mode cladding, which only emits diode pump light. The solid-state structure of the fiber laser makes it immune to environmental factors such as dust, moisture, and free-space air disturbances.
The electrical efficiency of the overall pumping method exceeds 50%, and the single-mode output power of a single module is about 2kW-3kW. The output of a single module can be used directly or in combination to provide a high-brightness output of more than 100 kW, making this fiber laser suitable for various industrial applications.
Operation method
Fiber lasers can be divided into continuous wave (CW), quasi-continuous wave (QCW), nanosecond pulse, ultrafast picosecond or femtosecond pulse and other light wave modes. Continuous wave lasers can provide stable output within the rated maximum output power, and can be modulated to 50kHz according to the output power, but the modulation will not increase their peak power. Continuous wave lasers are used in many fields. The most notable ones are cutting and metal welding. They can also be used for brazing, 3D printing, cladding and heat treatment.
The long pulse generated by 10 QCW lasers can increase the pulse energy and peak output power by 10 times, and the long pulse duration is 10?s-100000?s. For example, a QCW laser with an average power of 300W has a peak power of 3kW and a pulse energy of 30J. QCW lasers are mainly used for welding, drilling and special cutting operations, such as cutting highly reflective metals or other materials. The peak power range of the standard QCW model machine is 1kW-20kW, and the operating cost is much lower than other competitive laser technologies that can do the same output.
The nanosecond pulse Q-switched fiber laser can provide an average output power range from 10W to 2kW. In the range of 1ns-1000ns, the pulse duration can be fixed or adjustable (users can choose to pre-program). The typical laser pulse energy is within 10W-300W, which is close to the single-mode beam quality used for micro-processing, up to about 1mJ. Depending on the model, these lasers can be modulated from kilohertz to megahertz. The pulse laser with higher average power is used for high-speed surface treatment, and the pulse energy can reach 100mJ, which can realize a larger processing area.
Ultrafast picosecond and femtosecond fiber lasers have pulse durations ranging from 200fs to several picoseconds, with an average power of 10W-200W, and can be used in various microprocessing applications, including metals and non-metals.
The active laser core of a fiber laser can be doped with one or more active atoms to produce a standard output in several spectral ranges.
Wavelength range
Doping one or more active atoms in the active laser core of a fiber laser can produce a standard output in several spectral ranges . For example, doping with ytterbium (Yb) atoms can produce output between 1030nm and 1080nm; doping with erbium (Er) atoms can produce wavelengths between 1500nm and 1570nm; doping with thulium (Tm) atoms can produce 1900nm- 2050nm light. Double or triple the frequency of these basic lines, and it is a laser that can emit green beams (515nm-550nm) and ultraviolet beams (-355nm).
The reachable range of the Raman displacement of the fundamental wave ytterbium erbium is expanded to 1.15 µm-1.8 µm. The further doubling of the wavelength enables the fiber laser to work in the visible light range of 515nm-635nm. In addition, a hybrid solid-state laser pumped by a continuous-wave fiber laser doped with thulium or erbium can provide mid-infrared output in the range of 1.9 µm to> 5 µm.
