What will define the future of fiber lasers?
In recent years, with the improvement of technology, domestic fiber laser has gradually broken through the power limit, from 12KW to 20KW, the highest power has been launched on the market for 30KW fiber laser, the next step is 50KW. We are concerned and the competition is also who the laser output power is greater, but ignored who the beam quality is better.
Lasers have four main characteristics, which are high brightness, good directionality, good monochromaticity, and high coherence. These characteristics are related to each other and make lasers applicable to different scenarios.
The high brightness of laser is an important feature that distinguishes it from ordinary light sources, and increasing the power and brightness is also an eternal issue in the development of lasers. What is high brightness, expressed in technical language is to describe the beam quality of the index M2 the closer to 1.
Today let's take a look at what is high brightness, and the advantages and significance of high brightness.
? Laser beam characteristics
The laser emitted from the laser, is like this, first in the near field convergence, and then in the far field dispersion away
Where the beam waist radius w0 is the radius at which the laser beam converges in the near field to the minimum cross-section.
The Rayleigh length ZR is the position at which the beam waist increases by a factor of √2.
The far field is defined as the range beyond 4 times the Rayleigh length, and the near field is defined as the range within 4 times the Rayleigh length.
The far-field divergence angle θ characterizes the degree of divergence of the laser beam in the far field.
? Beam quality characterization
Beam quality is the core parameter characterizing the laser beam properties and is an important indicator of the laser to measure how well the laser beam is focused in a given situation. Commonly used methods to quantify beam quality are Beam Parameter Product (BPP) and M2 factor.
BPP (Beam Parameter Product): Beam Parameter Product, is defined as the beam waist radius (w0) multiplied by the far-field divergence angle (θ).
M2: Ratio of the beam parameter product to the beam parameter product of the fundamental mode Gaussian beam, convertible to BPP.
By the above formula, we can easily find that BPP is independent of wavelength, while M2 factor is related to laser wavelength.
The value of M2 factor is infinitely close to 1, which indicates the ratio between real data and ideal data. When the real data is closer to the ideal data, the better the beam quality is.
For a fiber laser at 1070 nm, the ideal parameters should be as follows.
When the fiber laser BPP or M2 parameter is closer to this value, the better the beam quality and the smaller the corresponding divergence angle.
? How to determine beam quality
Usually, we use a beam analyzer to measure the beam quality of the laser, allowing the analyzer to create relative motion with the optical path, collecting X, Y, and Z information at multiple locations, thereby determining the beam waist size, location, and divergence angle, and deriving the Rayleigh length and BPP or M2.
Commonly used are the knife-edge method and slit method, which are basically the same idea, that is, using a knife mouth or slit to scan over the beam, mapping the light field distribution of a tangent, and then moving up and down, mapping the tangent at different distances, and finally deriving a three-dimensional light field distribution.
Knife-edge method
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Slit method
Beam quality testing is often complex, but simply, we can approximate it based on the fiber core diameter and the numerical aperture (NA).
A beam of light, regardless of the angle range, can only be transmitted properly if the light enters the fiber within a critical incidence angle range, and the sine of this angle α is the numerical aperture NA of the fiber, i.e. NA = sinα, which reflects the ability of the fiber to receive light. It can be generally approximated as a picture.
? What do we usually mean by high-brightness lasers?
Brightness (Br) definition: power density per unit area with unit stereo angle. As we mentioned before, fiber laser core area picture, far-field stereo angle picture.
According to the above formula, it is easy to see: the so-called high brightness is to have a higher beam quality (i.e. smaller BPP or M2) at the same power.
As a global leader in high brightness lasers, GW Laser Tech focuses on the development of high brightness fiber lasers based on 976nm pump technology, leading the trend of fiber laser development.
GW Laser's single-mode 10μm extreme fiber output lasers with M2 <1.1 and 50kw 100μm fiber lasers have energy densities close to the physical limit.
Conventional 100μm core diameter single-mode 4kW laser M2 <1.3, multimode 12kW laser BPP <4.
GW Laser YLPS Series Single Module 4KW Laser
GW Laser YLPM series multi-module 20KW laser
? The significance and advantages of high brightness
In recent years, high-power lasers are gradually becoming the main force in the market, and fiber lasers are also moving towards higher power, 12KW lasers have become the standard for mainstream laser manufacturers now. Last year, the 20KW laser sales of GW Laser increased significantly; at present, the 40KW laser also gradually began to ship.
Most of the current high-power fiber lasers are made of multi-module beams, that is, the output of multiple laser modules coupled into a single fiber output, compared to the output fiber core of a single laser module, the output fiber core diameter of multiple modules combined to be larger, and the beam quality is correspondingly lower.
If we ignore the beam quality, through the multi-module beam combining scheme, higher power can be achieved. However, with technological progress and industrial upgrading, the manufacturing industry will gradually move toward high-end, which will inevitably put forward higher and higher requirements for lasers, not only to meet the increase in power but also to pay more attention to brightness. Those high-power lasers that focus on increasing power and not on brightness will soon be eliminated from the market.
From the very beginning, GW Laser Tech has been dedicated to the research and development of high-brightness lasers, focusing on both increasing power and brightness. Through the optimization of single laser module technology, fiber fusion, and beam combining solutions, we have achieved further improvement in laser brightness. Under the same power conditions, after the same optical system collimated focus, the spot at the focal point is smaller and the energy density is higher. This is directly reflected in the laser processing application: faster-processing speed under the same power; less power is required under the same processing speed.
For example, the YLPM series 20KW laser cuts faster than other lasers with the same power, and this advantage is especially obvious in cutting high anti-materials.
High-brightness lasers are an important direction in the development of the laser industry, and the current high-power laser market has become significantly homogenized, with major laser manufacturers moving in the direction of superimposed power.
GW Laser not only cares about the increase of laser power but also pays more attention to the improvement of laser brightness. In the future, we will continue to explore the direction of high brightness, so that the laser has better beam quality and processing performance to help customers improve processing efficiency.