Fiber lasers have a wide range of applications, and subdivision types can meet special needs.
There are many classification methods for fiber lasers, among which the most common are classified by working mode, band range and medium-doped rare earth elements.
Lasers are generally named according to one or two of these three categories.
For example, the YLM-QCW series of IPG translates into nearly continuous ytterbium-doped fiber lasers.
Fiber lasers have a wide range of applications.
Different subdivided lasers have different characteristics and suitable application fields.
For example, the mid-infrared range is safe for human eyes and can be strongly absorbed by water. It is an ideal medical laser source;
Erbium-doped fiber can open the window of optical fiber communication due to its suitable wavelength, which is widely used in the field of optical fiber communication;
Due to its visibility, the green laser is essential in entertainment and projection.
Fig. 1 Application diagram of laser subdivision and classification corresponding to relevant industries
The peak power of the pulsed laser is high and the processing speed of the quasi-continuous laser is fast.
According to the working mode, fiber lasers can be divided into mode-locked fiber lasers, Q-switched fiber lasers, quasi-continuous fiber lasers and continuous fiber lasers.
The technical approaches to realize pulsed fiber laser mainly include Q-switching technology, mode-locking technology and seed source main oscillation power amplification (MOPA) technology.
Mode lock technology can achieve femtosecond or picosecond pulse output, and the peak pulse power is high, generally in the order of megawatts, but the average output pulse power is low;
- Switched fiber laser can obtain pulsed laser with nanosecond pulse width, kilowatt peak power and megajoule pulse energy.
- The pulse width of the quasi-continuous laser is microseconds, and the continuous laser is continuously supplied with energy by the pump source to produce laser output for a long time.
Fig. 2 Fiber laser working mode and pulse width
CW fiber laser is the main product of high power laser.
CW laser output is continuous, widely used in the fields of laser cutting, welding and cladding.
The laser pump source supplies energy continuously and produces laser output for a long time, so as to obtain continuous laser.
The number of particles at each energy level and the radiation field in the cavity have a stable distribution.
Its working characteristic is that the excitation of the work material and the corresponding laser output can be carried out continuously for a long time interval.
The fiber laser excited by continuous light source is a continuous fiber laser.
Compared with other types of lasers, continuous fiber lasers can achieve relatively high power. IPG has produced a 20,000-watt single-mode continuous fiber laser, which is often used in the fields of laser cutting, welding and cladding.
The quasi-CW fiber laser can operate in two modes, which can significantly improve the processing speed
Quasi CW laser can work in continuous and high peak power pulse mode at the same time.
According to the IPG official website, the peak power and average power of the traditional CW laser are always the same in CW and CW/modulation mode, while the peak power of the quasi-CW laser in pulse mode is 10 times that of the average power.
Therefore, microsecond and millisecond pulses with high energy can be generated at repetition frequencies from tens of hertz to thousands of hertz, and average power and peak power of several kilowatts can be realized.
The quasi-CW fiber laser will provide higher electro-optical conversion efficiency and significantly improve processing speed and production efficiency.
Compared with other laser systems, the quasi-CW fiber laser can provide ten times increment of photoelectric conversion efficiency and can achieve more than 30% electro-optical conversion efficiency under passive cooling scheme.
Due to its high average power and pulse repetition rate, its processing speed is 3-4 times that of most lasers.
The significantly reduced energy cost, the absence of consumables and spare parts, the low maintenance demand and the absence of preheating time requirements will lead to cost optimization.
The pulsed fiber laser can compress energy and produce peak power.
Pulsed fiber lasers are divided into Q-switched fiber lasers and mode-locked fiber lasers.
Q-switching technology compresses laser energy into a short time interval to form a laser output with high peak power and narrow pulse width.
The principle of Q switching is to add a device with adjustable loss to the laser.
In most weather areas, the laser loss is very large and there is almost no light output.
In a short time, reduce the loss of the device, so that the laser output is a short, high-intensity pulse.
Q-switch is the core device of Q-switched technology, which can realize Q-switched fiber laser actively or passively.
Q-switched pulse fiber laser has the characteristics of high peak power, high single pulse energy and optional spot diameter.
It is widely used in marking, precision processing, graphic marking, deep engraving, sheet precision cutting, drilling and other fields of non-metallic stainless steel, gold, silver, copper, aluminum and non-high reflection material.
In terms of marking application, compared with CO2 laser, the cost is lower and the performance is more stable.
The mode-locked pulse fiber laser generates ultrashort pulses by active mode locking or passive mode locking.
Limited by the response time of the modulator, the pulse width generated by active mode locking is wide, generally on the order of picoseconds;
Passive mode locking uses passive mode locking devices with short response time and can produce femtosecond pulses.
The brief principle of mode locking is to take appropriate measures to make the mutually independent longitudinal modes in the resonator have a certain phase relationship.
Even if the phase difference of adjacent longitudinal modes is constant, the laser will produce pulses with extremely narrow pulse width and high peak power.
The mode-locked pulse laser has the advantages of excellent beam quality, ultra-short pulse width and high pulse energy.
It is suitable for micromachining of various materials, including metal, glass, ceramics, silicon and plastics.
In the medical field, mode-locked lasers are also used in laser scalpels or in ophthalmic surgery.
For example, photochemical effects are also used for some skin care.
Due to the short pulse characteristics and high peak power, mode-locked lasers are widely used in various imaging, microscopy and spectroscopy methods.
They are also used in the areas of electro-optical sampling measurement, distance measurement, frequency measurement and timing in integrated electronic circuits.
Near infrared light is the main one, and green light and far infrared light have their own characteristics.
The laser directly emitted by the fiber laser is mainly near-infrared light with a wavelength between 960nm-2.05μm.
In order of wavelength from short to long, the laser category encompasses all laser types from X-ray to far infrared, with wavelengths ranging from 0.001 nm to 1000 microns.
Among them, the laser directly emitted by the fiber laser is mainly in the near-infrared part.
However, to meet the needs of different applications, fiber lasers can produce visible light through frequency doubling, and the main application is green light;
Mid-infrared light can be emitted by doping fluorine into the optical fiber.
Fig.3 List of different fiber optic wavelengths
Table 1. Lasers by wavelength
| Name | wavelength range | Main Products |
| Far infrared laser | 30 ~ 1000 microns | Molecular gas laser, free electron laser |
| Mid-infrared laser | 3 ~ 30 microns | CO2 molecular gas laser |
| Near infrared laser | 0.76 ~ 3 microns | Fiber laser, CaAs semiconductor diode laser, partial gas laser |
| Visible laserNear infrared laser | 380nm ~ 780nm | Ruby laser, He Ne laser, argon ion laser, krypton ion laser |
| Near-ultraviolet laser | 200nm ≈ 400nm | Nitrogen molecular laser, xenon fluoride excimer laser, krypton fluoride (KrF) excimer laser |
| Vacuum ultraviolet laser | 5nm ~ 200nm | Hydrogen excimer laser (H), xenon excimer laser (Xe) |
| X-ray laser | 0.001nm ~ 5nm |
The mid-infrared fiber laser is safe for human eyes and is an ideal medical laser source.
The wavelength of mid-infrared laser is mainly about 23 microns to 3.9 microns, which needs fluorinated glass fiber medium doped with rare earth ions to excite.
From the fluorescence spectrum generated by the infrared transition of fiber laser in the figure below, it can be seen that holmium-doped ion (Ho3+) and erbium-doped ion (Er3+) can be directly generated by excitation under conditions appropriate averages.
The fluorine glass fiber laser has high efficiency and output power in the range of 2.3~3.5μm, while the wavelength is greater than 3.5μm.
There are very few materials that can meet the low phonon energy required for optical fiber transmission and transition radiation of rare earth ions.
Single doped Ho3+ fluorine fiber laser produces 3.9μm band laser at low temperature, which is the longest direct output wavelength at present.
Fig.4 Relationship between maximum output power and emission wavelength of different rare earth ion fiber lasers
Due to its wavelength characteristics, the mid-infrared laser can open the atmospheric window and is widely used in laser guidance, positioning and measurement.
In military affairs, the application of directional laser energy and long-distance transmission through the atmospheric transmission window requires strong beam energy.
In infrared missile countermeasure, mid-infrared laser can obtain 3~5μm band atmospheric transmission window.
The mid-infrared fiber laser with several kilowatts of single-mode output can be even more widely used in national defense warfare platforms such as anti-cruise missiles, rocket guidance and UAV airspace reconnaissance.
Mid-infrared fiber laser has been widely used in the medical field because of its strong directivity and safety for human eyes.
The mid-infrared laser band is safe for human eyes and can be strongly absorbed by water.
Due to the strong directionality of the laser, the tissue penetration depth can be shallow and the physical damage area can be very small in laser surgery, so as to achieve high precision.
In modern medicine, mid-infrared laser in medical applications mainly uses photothermal effect to treat or remove diseased tissue.
It has been widely used in orthopedics, gastroenterology and urology.
It has become an ideal medical laser light source for urinary tissue ablation and cutting, vaporization and removal of failed organs.
In the process of cutting tissues rich in lipids, bones and proteins, the use of mid-infrared laser will cause minor damage.
The green fiber laser has high spectral brightness and 84% conversion efficiency
Fiber laser can obtain green light output by doubling the frequency.
Although the frequency-doubled green fiber laser is not a green fiber laser in the strict sense because its activation medium does not directly deliver the 532 nm laser beam, this type of fiber laser provides a narrow range of pulse duration and repetition frequency of up to 600kHz.
The laser source with high spectral brightness promotes efficient conversion, achieving 84% conversion efficiency and more than 20% electro-optical conversion efficiency.
It is feasible to upgrade to high power at 355 and 266 nm.
Green laser is widely used in printing, medical treatment, data storage, military, biology and other fields.
For example, IPG's green fiber laser can be used in particle imaging, velocity measurement/flow visualization, imaging diagnostics and surgery, optical capture/optical tweezers, solar cell manufacturing, manufacturing inspection and quality control , holography and interferometry, entertainment and projection, etc. .
The ytterbium-doped fiber is dominant, and the erbium-doped thulium-doped fiber has its own working wavelength.
Fiber laser mainly uses fiber doped with rare earth elements as the gain medium, and different rare earth elements correspond to different working wavelengths.
Doped fiber adds impurities such as rare earth ions to the fiber core, which will lead to the modification of the fiber and show the laser effect.
The working principle is that the pump light is first coupled to the gain medium doped with rare earth ions through the coupling system, and then the rare earth ions in the doped core absorb the photon energy of the pump and produce energy level transition.
For example, rare earth ions such as erbium (Er3+), praseodymium (Pr3+), thulium (Tm3+), neodymium (Nd3+), and ytterbium (Yb3+) can be used as dopants to make optical fibers. and then made using a doped fiber amplifier (XDFA) and fiber laser (XDFL).
Different rare earth elements work in different wavelength ranges, but are in the near-infrared range.
Fig. 5 Operating wavelengths of rare earth ions in commonly doped cores.
Ytterbium-doped fiber laser is the leading force in the laser industry.
Ytterbium-doped fiber laser has developed rapidly due to its high stability, good beam quality and high tilting efficiency.
Ytterbium-doped fiber has many advantages.
The fiber laser developed by ytterbium-doped fiber has high tilt efficiency and optical conversion efficiency, and can achieve high-power laser output in the 1m band.
Therefore, it has attracted a lot of attention and developed rapidly.
It has become the main guiding force in the laser industry and has good application prospects in industrial processing, medical treatment, national defense and other fields.
Most Ruike laser products use ytterbium-doped fiber.
Table 2. Comparison of the main mirror-doped optical fiber products of domestic and foreign companies
| Company | Adopt technology | Product status/price | Core diameter（μm） | Lining diameter | Central numerical aperture NA |
| Nufern | Super large mode field mirror doped fiber (three coatings) | SellUSD 1030/M | 290.0±20.0 | 400±18 | 0.110±0.010 |
| Night | Double coated ytterbium doped fiber with large mode field | Sell | 20.0±1.5 | 400±10.0 | 0.070±0.005 |
| Changfei optical fiber | Double coated ytterbium fiber with large mode field | Sell | 20.0±2.0 | 400±15.0 | 0.06±0.01 |
| Lighthouse technology | Double coated ytterbium doped fiber | Sell | 20.0±2.0 | 400±5.0 | 0.075±0.005 |
| Wuhan Ruixin | Double coated ytterbium doped fiber with large mode field | Sell | 20.0±1.5 | 400.0±10.0 | 0.065±0.005 |
Ytterbium-doped fiber lasers are mainly used in continuous lasers and pulsed Q-switched lasers.
Due to the simple structure of the ytterbium ion energy level and small particle loss, the laser has high conversion efficiency and low thermal effect under high power operation, and the gain bandwidth is large (975nm ~ 1200nm).
At the same time, the lifetime of ytterbium ion is relatively long, generally about 1 millisecond.
These factors lead to Q-switching technology.
Therefore, ultrashort pulse output was realized in pulsed laser.
In the aspect of CW laser, the output power of the ytterbium-doped fiber laser has reached the order of 10,000 watts.
Erbium-doped fiber laser is a unique optical fiber communication window
Erbium-doped fiber laser has the characteristics of safe wavelength and ultra-high pulse energy. Erbium-doped fiber laser can realize single-mode operation, with extremely narrow linewidth, good monochromaticity and stability.
Erbium ion has a wide gain bandwidth, which can aggravate the multimode oscillation in the laser cavity, so as to realize ultrashort pulse laser.
Due to its unique characteristics for human eye safety (“human eye safety” refers to the fact that the laser with a wavelength of 1.5 μm is significantly lower than the harm limit for the human eye), it has a wide range of practical applications in the areas of free-space optical communication, lidar, environmental sensing, parts calibration and industrial processing.
Erbium-doped fiber has been widely used in the field of optical fiber communication due to its suitable wavelength.
As the erbium-doped fiber has high gain at the wavelength of 1550 nm, its gain spectral profile of about 40 nm corresponds to the best low-loss window in optical fiber communication, which has potential application value.
Thulium-doped fiber laser can improve absorption characteristics of aqueous materials
Thulium-doped fiber laser has the characteristics of low threshold, high efficiency and good beam quality.
Thulium-doped fiber laser is the research point of fiber laser in the safe wavelength field for human eyes, and thulium-doped fiber laser can work in the S-band (150 – 75 mm).
It plays a very important role in developing the frequency space of potential communication resources and improving the capacity of optical fiber communication system.
Continuous and Q-switched thulium-doped fiber lasers have developed to higher average power in recent years.
Now, a number of suppliers can provide commercial pulsed lasers with an average power of 10W.
Thulium-doped fiber laser is widely used in medical laser treatment, lidar, space light remote sensing and other fields.
The output wavelength of thulium-doped fiber laser is about 2μm.
The strong absorption band of liquid water is about 1950 nm, which is close to the wavelength of standard thulium fiber laser, so the absorption characteristics are significantly improved.
Water generally exists in many organic and inorganic compounds, which means that a large number of materials improve absorption characteristics in the 2μm spectral range.
Therefore, thulium-doped fiber laser is considered an ideal light source for medicine, eye safety, ultrafast optics, short-range remote sensing and biology, and has good development prospects.
At the same time, in the field of medicine, thulium-doped fiber laser also has many applications, including accelerated vaporization, ultra-fine cutting technology and coagulation hemostasis in medicine.
The high-power thulium-doped fiber laser can not only be used for the safe wavelength of human eyes and lidar light source, but also can be used as a solid-state crystal laser pump source to achieve even more the output of the infrared laser with longer wavelength.
Fig.6 Absorption characteristics of liquid water at different wavelengths
Fiber laser has excellent performance advantages and obvious replacement effect.
The carbon dioxide laser has low light conversion efficiency and high cost.
The carbon dioxide laser is a type of molecular laser.
It is one of the common high power CW lasers.
The main material is the carbon dioxide molecule.
The main structure of CO2 laser includes laser tube, optical resonator, power supply and pump.
The main feature is that the output power is large and continuous work can be carried out, but the structure is complex, the volume is large, and maintenance is difficult.
Fig.7 Structure of carbon dioxide laser
Particle number inversion is the key to carbon dioxide laser luminescence.
The working substances in the carbon dioxide laser include carbon dioxide, nitrogen and helium. After the DC power supply is input, the nitrogen molecules in the mixed gas will be excited by the impact of electrons.
When excited nitrogen molecules collide with carbon dioxide molecules, they transfer energy to the carbon dioxide molecules, so that the carbon dioxide molecules transition from the low-energy level to the high-energy level to form particle number inversion and emit laser.
Fig.8 Schematic diagram of the carbon dioxide laser emission process
Optical fiber and carbon dioxide laser have their own advantages, so different tools should be selected according to different needs.
Of the currently widely used cutting technology, fiber laser and CO 2 laser have their own advantages and disadvantages in the face of specific application requirements.
They cannot completely replace each other, but they need to complement each other and coexist.
In terms of types of processing materials, due to the absorption effect, fiber lasers are not suitable for cutting non-metallic materials, while conventional CO2 lasers are not suitable for cutting high-reflectivity materials such as copper and aluminum;
In terms of cutting speed, CO 2 has advantages in sheet metal with a thickness > 6mm, while the fiber laser cuts the sheet faster;
The workpiece needs to be penetrated before laser cutting, and the drilling speed of CO2 is significantly faster than fiber laser;
In terms of cutting section quality, CO2 laser is better than fiber laser as a whole.
Table 3. Comparison between fiber laser and carbon dioxide laser
| fiber laser | carbon dioxide laser | |
| Cutting material | Non-metallic materials cannot be cut | Highly reflective materials have poor adaptability |
| Cutting speed | Obvious advantages below 3mm | Carbon dioxide has an advantage when it is greater than 6 mm. |
| Penetration efficiency | The speed is relatively slow | The greater the thickness, the more obvious the advantage |
| Section quality | A little worse | Better roughness and verticality |
Fiber laser has higher light conversion efficiency and lower cost.
According to the calculation, the cost of using fiber laser is 23.4 yuan/hour, the cost of using carbon dioxide laser is 39.1 yuan/hour, among which the energy cost of fiber laser is 7 yuan/hour, water cooling cost is 8.4 yuan/hour, and other costs are 8 yuan/hour;
The energy cost of carbon dioxide laser is 21 yuan/hour, the water cooling cost is 12.6 yuan/hour, and other costs are 5.5 yuan/hour.
Table 4. Cost comparison between fiber laser and carbon dioxide laser
| fiber laser | carbon dioxide laser | |
| Power (kw) | 3 | 3 |
| Light Conversion Efficiency | 30% | 10% |
| Power consumption (kw) | 10 | 30 |
| Electricity price (yuan/kWh) | 1 | 1 |
| Charging duration | 70% | 70% |
| Energy cost (yuan/hour) | 7 | 21 |
| Power of water cooling equipment (kw) | 12 | 18 |
| Electricity price (yuan/kWh) | 1 | 1 |
| Charging duration | 70% | 70% |
| Water cooling cost (yuan/hour) | 8.4 | 12.6 |
| Cost of consumables (yuan/hour) | 3 | 2.5 |
| Module consumption cost (yuan/hour) | 5 | |
| Media cost (yuan/hour) | 1 | |
| Conventional point solution (yuan/hour) | two | |
| Other costs (yuan/hour) | 8 | 5.5 |
| Usage cost (yuan/hour) | 23.4 | 39.1 |
YAG laser has low energy conversion efficiency or is gradually replaced.
YAG laser generally refers to Nd. YAG laser (rubidium doped yttrium aluminum garnet crystal) belongs to solid state laser.
The content of rubidium atoms in the crystal is 0.6~1.1%, which can produce pulsed laser or continuous laser, and the emitted light is infrared with a wavelength of 1.064μm.
Nd. YAG laser generally uses krypton or xenon lamp as pump lamp, because only some specific wavelengths of pump light will be absorbed by Nd ions, and most of the energy will be converted into thermal energy.
Generally, the energy conversion efficiency of YAG laser is low.
Fig. 9 Simple structure of the Nd:YAG laser
With the development of fiber laser, YAG laser can be gradually replaced.
YAG laser is mainly used in cutting and welding processes in industry, but with the development of fiber laser, YAG laser can be gradually replaced by fiber laser.
In the cutting area, the YAG laser has a low purchase cost and can cut highly reflective materials, but has low processing power, high energy consumption rate and slow cutting speed, while the fiber laser has high energy efficiency, without adjustment and maintenance;
In the field of welding, after the emergence of the quasi-continuous fiber laser, it began to quickly replace the pulsed Nd:YAG laser.
Compared with YAG laser, quasi-CW fiber laser can deliver pulse energy from several joules to tens of joules under microsecond to millisecond pulse width.
Its high average power and pulse repetition frequency significantly improve processing speed and production efficiency.
It is equivalent to having the drilling and welding advantages of YAG laser and the cutting ability of CO2 laser at the same time.
It has a wider range of applications.
Table 5. YAG laser vs. fiber laser
| Laser | YAG laser | fiber laser |
| Main composition | Pump lamp, Nd:YAG, resonant system | Semiconductor pump, fiber optic resonance system, transmission system |
| wall outlet efficiency | 4%~5% | About 30% |
| Machining angle | Low acquisition cost, capable of cutting highly reflective materials | Cutting power is high, efficiency is fast, and high power can be obtained in a small package |
| Cost perspective | Mature technology is relatively cheap | With the gradual development of technology, power consumption is small |
| Maintenance angle | No optical lens, free from adjustment and maintenance |
There are still limitations in semiconductor laser technology at this stage
Semiconductor lasers, also known as laser diodes, use semiconductor materials as working materials.
Common working materials include gallium arsenide and cadmium sulfide.
There are three excitation modes: electrical injection, electron beam excitation and optical pumping.
The main advantages of semiconductor lasers are small volume, low efficiency and high power consumption.
They are widely used in laser communication, laser therapy and other fields.
Furthermore, semiconductor lasers are generally used as the pump source of fiber lasers.
Taking electrical injection semiconductor laser as an example, GaAS (gallium arsenide), InAS (indium arsenide), Insb (indium antimonide) and other materials are generally added to the semiconductor material to make a semiconductor surface junction diode.
When a large enough current is injected into the diode, the electrons (with a negative charge) and holes (with a positive charge) in the intermediate active region spontaneously compose themselves and release the excess energy in the form of photons.
Then, the laser is formed after resonator screening and amplification.
Fig. 10 Schematic diagram of the simple structure of the semiconductor laser
The direct semiconductor laser has obvious characteristics and a wide range of downstream applications.
The direct semiconductor laser has a compact structure, low maintenance cost and electro-optical conversion efficiency of up to 47%. It is mainly used in industry for welding and cladding.
Low-power semiconductor lasers are mainly used in plastic welding and tin welding.
Through optical fiber output welding, contactless remote operation is realized, which is convenient for integration with automatic production line;
Direct kilowatt-class semiconductor can be used for hardware plating and soldering.
It has the characteristics of large light spot and high electro-optical conversion rate.
In the field outside of industry, semiconductor lasers are also widely used in the military, information, medicine and life sciences.
Table 6. Direct semiconductor laser applications
| Field | Subdivision Application | Application scenario |
| Industry | Welding | Plastic processing, hardware welding |
| Coating | Steel, aerospace | |
| Military | Radar | Lidar system, automatic identification and correction system |
| Guidance and Fuze | Laser beam guidance, laser sight and warning sight | |
| Information | Signal communication | Fiber Optic Communication Light Source |
| Information search | Spectral analysis, optical computing and optical neural network | |
| Medical care | Clinical operation | Soft tissue resection and tissue union |
| Life science research | Optical tweezers |
Semiconductor lasers have potential for processing applications, but are limited by technical defects.
Research shows that direct semiconductor laser has strong application potential in materials processing and has better cutting speed and quality than fiber laser and carbon dioxide laser.
However, the biggest disadvantage of semiconductor lasers is poor beam quality at high laser power.
Currently, industrial semiconductor lasers are limited to some processing, such as electroplating, brazing and increasingly high-power welding.
Therefore, semiconductor lasers are unlikely to revolutionize the entire field of materials processing or replace other light sources in the coming years.
Table 7. Comparison of direct semiconductor laser, fiber laser and carbon dioxide laser cutting processes
| Direct semiconductor laser | fiber laser | carbon dioxide laser | |
| Common band（μ m） | 0.97 | 1.07 | 10.6 |
| Electro-optical conversion rate | 47% | 30% | 10% |
| Metal absorptivity | 0.97 | 1.07 | 10.6 |
| Sheet cutting speed | 47% | 30% | 10% |
| Maximum cutting thickness (mm) | 15 | 12 | 25 |
| Cut quality (above 4mm) | higher | higher | Lower |
| Output beam quality | The fastest | Faster | Slower |
According to the above analysis, we believe that compared with CO2 laser and YAG laser, fiber laser has obvious cost and application advantages or will be gradually replaced.
At the same time, semiconductor lasers are still limited by the technical bottleneck.
They currently have limitations and are unlikely to replace other light sources in the coming years.
Therefore, there is ample room for improvement of fiber laser permeability.
