Category: Wavelengths & Laser Types

High-power fiber lasers in laser processing

The major position in the laser processing field is rightly being given to the high-power fiber laser due to such qualities as high beam quality, energy efficiency, space efficiency, stability, and reliability. The fiber laser is a laser that uses an optical fiber as the active medium, which usually has a rare-earth-doped core. The major active element used in the fiber lasers for material processing is ytterbium. This element provides light absorption (available for pumping) at wavelengths of 900-1000 nm, and fluorescence that causes laser oscillation lies at 1000-1100 nm.

Market growth and performance improvements

Over the last decade, the performance advanced in high-power fiber lasers has been particularly impressive. It is making high-power fiber lasers a successful, fast-increasing commercial business currently worth $800 M/year, with a compound annual growth rate of about 13%, which is the highest among the different laser technologies. The fiber technology has grown quite diverse and mature, and can provide an excellent platform for fabricating result, high-performance laser systems. The core and cladding structures can be tailored appropriately to control the beam modality, optical nonlinearities, and the power.

Features and advantages of high-power fiber lasers

High-power fiber lasers are much more progressive and promising than traditional lasers using solids or gases as the active medium in many aspects. To ensure the high beam quality of fiber lasers, it is necessary to select the appropriate core diameter and the difference in relative refractive indices, which can reduce the number of transverse modes. The CO2 laser also provides a high beam quality. In addition to this, fiber lasers and fiber laser systems based on a thin optical fiber with a diameter of several hundred micrometers as the active medium can be easily cooled, thereby attaining high power output while maintaining laser beam quality.

High-power fiber lasers have very low loss of pump and laser light because they are both confined and guided in the low-loss fiber core. The high quantum efficiency of ytterbium serving as the active element leads to 60-70% efficiency in energy conversion from pump light to laser light. Fiber laser systems achieve a high output power with a high energy conversion efficiency while maintaining a high beam quality. Owing to the very high energy conversion efficiency and a resonator consisting of fine fiber and small optical components, high-power fiber lasers have a far smaller heat dissipation mechanism and power supply, and thus far smaller overall dimensions and weight than traditional high-power lasers. These lasers constructed by fusion-splicing optical fibers are not influenced by vibration, shock, or temperature changes, and therefore have stable output power and stable high beam quality. Besides the above-mentioned factors, high-power fiber lasers are practically maintenance-free due to the fact that the paths of the beam are not exposed to the atmosphere.

Applications of Ultrafast Optics

Ultrafast optics has been a very rich research field, and today short-pulsed laser systems find different applications in areas of fundamental research as well as for medical applications. Ultrafast laser systems are used for time-resolved studies in chemistry, optical frequency metrology, terahertz generation, spectroscopy and microscopy, and optical coherence tomography.

The cornerstone of ultrafast optics is the mode-locked lasers, and developments of mode-locked lasers have been a huge research field in itself. In the last few years, mode-locked lasers have moved from just offering a low-cost, rugged, and compact source of ultrashort pulses to offering state-of-the-art ultrashort pulses.

Mode-locked Lasers and Their Prospects

Mode-locked lasers are an extremely promising type of laser.

Historical Background

The history of mode-locked lasers began after the first demonstration of continuous-wave lasing in 1960; the creation of the first mode-locked laser occurred at Bell Laboratories in New Jersey. The term “mode-locking” refers to the requirement of phase locking many different frequency modes of a laser cavity. This locking results in inducing a laser to produce a continuous train of extremely short pulses rather than a continuous wave of light. Mode-locked lasers generate short pulses of intense coherent light. Laser cavities can support many different frequencies or resonant modes. A train of picosecond or femtosecond pulses can be produced by actively or passively controlling the light in the cavity so that those different resonant modes interfere.

The Concept of Mode-locking

The term mode-locking resulted from an interpretation in the frequency domain: in the mode-locked state, axial resonator modes are oscillating with a locked relative phase.
Several types of lasers are particularly attractive for mode-locking:

• Solid-state bulk lasers, based on ion-doped crystals or glasses, are today the dominant type of mode-locked lasers. They allow for very short pulses, very high pulse energies and/or average output powers, high or low pulse repetition rates, and high pulse quality;
• Fiber lasers can also be mode-locked for generating very short pulses with potential setups;
• For applications in optical fiber communications, semiconductor lasers can be built as mode-locked diode lasers;
• Dye lasers have a broad gain bandwidth, allowing for very short pulses. These lasers have been largely replaced with solid-state lasers, as these were able to deliver similar or better performance.

High-power fiber lasers

High-power fiber lasers are extraordinary devices. The laser has been the most significant, after the transistor, technological invention since World War 2. Lasers and laser systems find widespread application in different fields of science, engineering, and technology. They can be used for scanning barcodes, machining and welding, reading compact discs, printing paper, precision surgery, enabling high-speed communications, finding distances, guiding precision munitions, and driving controlled nuclear fusion. Pulsed fiber lasers are applied in elevated tasks such as the production of controlled nuclear fusion and laser eye surgery (ultrafast lasers), down to the mundane, such as cosmetic hair removal. The impressive increase in lasers’ peak power has been overwhelming over the last 50 years: the peak power attainable in a laser pulse has increased by roughly a factor of 1,000 every 10 years. The ability to produce high powers with lasers stems from the quantum mechanics that enable their operation.

How lasers work: the basics

The easiest way to determine the laser is to characterize it as an amplifier. The laser works by pumping energy into electrons of atoms in a substance, called the gain material. These atoms can be assembled in a number of forms, and many different media suitable for lasers have been developed. The active atoms or molecules in laser media can be in gaseous forms, such as the neon atoms in the ubiquitous helium-neon laser. They can also be semiconductor materials, such as gallium arsenide, used in the diode or solid-state lasers. Or they can be embedded in crystals such as the chromium ion in ruby. High-power fiber lasers capable of continuous output powers ranging from hundreds of watts to thousands of watts present exciting opportunities for rapid, directed delivery of energy.

Advantages of high-power fiber lasers

Beam quality and efficiency

High-power fiber lasers are much more progressive and promising than traditional lasers using solids or gases as the active medium in many aspects. In order to ensure the high beam quality of fiber lasers, it is necessary to select the appropriate core diameter and difference of relative refractive indices, which can reduce the number of transverse modes. The CO2 laser also provides a high beam quality. In addition to this, fiber lasers and fiber laser systems based on a thin optical fiber with a diameter of several hundred micrometers as an active medium can easily be cooled and therefore attain high power output while maintaining the laser beam quality. Also, high-power fiber lasers have very low loss of pump and laser light because they are both confined and guided in the low-loss fiber core. The high quantum efficiency of ytterbium serving as the active element leads to 60-70% efficiency in energy conversion from pump light to laser light.

Compact design and reliability

In virtue of these factors, laser systems on the basis of the optical fiber achieve a high output power with a high energy conversion efficiency while maintaining a high beam quality. Owing to the very high energy conversion efficiency and a resonator consisting of fine fiber and small optical components, high-power fiber lasers have a far smaller heat dissipation mechanism and power supply, and thus far smaller overall dimensions and weight than traditional high-power lasers. These lasers, constructed by fusion-splicing optical fibers, are not influenced by vibration, shock, or temperature changes, and therefore have stable output power and stable high beam quality. Besides the above-mentioned factors, high-power fiber lasers are practically maintenance-free due to the fact that the paths of the beam are not exposed to the atmosphere.

The designers, developers, and users of high-power laser systems discuss design approaches, methods of enhancing performance, new applications, and user requirements.

Key Features of Tunable Fiber Lasers

The distinctive feature of the tunable fiber laser is the wavelength of operation, which can be altered in a controlled manner. Only several types of fiber lasers allow continuous tuning over a significant range. Tunable fiber lasers are usually operating in a continuous way with a small emission bandwidth, although some Q-switched and mode-locked fiber lasers can also be wavelength-tuned.

Types of Tunable Fiber Lasers

There are many types and categories of tunable fiber lasers, such as excimer fiber lasers, gas-fiber lasers (CO2 lasers, He-Ne lasers, and others), dye fiber lasers (liquid and solid state), semiconductor crystal and diode lasers, and free electron lasers. Tunable fiber lasers find applications in spectroscopy, photochemistry, atomic vapor laser isotope separation, and optical communications.

Pricing Challenges and Market Dynamics

Prices for fixed and tunable fiber lasers are not yet equivalent. Although some tunable types are priced like fixed-wavelength devices, they are tunable over only very narrow ranges, about 3-4 nm. Those fiber lasers that can be tuned across wide wavelength ranges remain at least two or three times as expensive as their fixed counterparts.

The high price of tunable fiber lasers is explained by specific features: the increased complexity of manufacturing them, the extra testing required, and the newness of the technology, which has yet to reach true volume demand.

Future Price Reductions

As demand for tunable lasers rises, their prices will come down. Laser manufacturers claim the price premium for a widely tunable laser will drop to about 15-20 percent above that of a fixed laser anyway.

Applications in Optical Networks

The significantly favorable changes in demand for tunable fiber lasers will occur in parallel with their application to make optical networks more flexible.

Network Challenges

Fiber optic networks based on different types of fiber optic devices are essentially fixed: the optical fibers are connected into pipes with huge capacity but little reconfigurability. It is almost impossible to change how that capacity is deployed in real time.

Benefits of Tunable Fiber Lasers

In addition to this, there is a problem in choosing a wavelength for a channel: as traffic is routed through a network, certain wavelengths may already be in use across certain links. Tunable fiber lasers will ease the switch to alternative channels without swapping hardware or re-configuring network resources.

Role in Future Networks

The benefits gained from the use of tunable fiber lasers are in the time it takes to actually deliver different types of services. Undoubtedly, tunable fiber lasers can dramatically improve fiber optic networks’ efficiency and will play an important role in enabling future dynamically reconfigurable optical networks, along with optical switches and semiconductor optical amplifiers.

Ti:Sapphire Lasers

Titanium-doped sapphire (Ti:Al2O3 or Ti:Sapphire) lasers and amplifiers have enabled countless applications in fundamental research in physics, biology, and chemistry since their invention in the early 1980s. Ti:Sapphire lasers play an important role across a wide range of photonics applications, including multicolor ultrafast spectroscopy, multiphoton deep-tissue imaging, terawatt and petawatt physics, and “cold” micromachining.

Key Characteristics

Speaking specifically, Ti:Sapphire lasers are tunable fiber lasers which emit red and near-infrared light in the range from 650 to 1100 nanometers. These lasers are mainly used in scientific research because of their tunability and their ability to generate ultrashort pulses. Ti:Sapphire lasers possess high laser cross sections, which in turn minimize their Q-switching instabilities. Pumping of Ti:Sapphire lasers is carried out with other lasers having wavelengths of 514 to 532 nm; it includes Nd:YVO lasers, frequency-doubled Nd:YAG lasers, or argon-ion lasers.

Historical Development

The first reported Ti:Sapphire laser operation was performed in June 1982 by Peter Moulton at the 12th International Quantum Electronics Conference in Munich, Germany.

In 1998, Spectra-Physics offered the first commercial Ti:Sapphire laser, a broadly tunable continuous-wave model, and in late 1990, the first ultrafast Ti:Sapphire laser, a picosecond mode-locked oscillator. Further developments in this field led to a sudden paradigm shift rarely seen in research.

Unique Performance

Ti:Sapphire laser systems are unmatched in their characteristics for delivering a combination of broad spectral bandwidth, a range of repetition rates, wide tunability, and high-average-power levels. Since most other broadband lasers gain media have relatively poor thermal properties, Ti:Sapphire lasers offer a unique performance for use in ultrafast laser systems.

Applications of Ti:Sapphire Lasers

The main applications of Ti:Sapphire lasers are in research laboratories, in particular in spectroscopy. The large tuning range makes these fiber lasers attractive for generating tunable sub-picosecond pulses at short wavelengths.

• Atmospheric Studies. Ti:Sapphire lasers are used in NASA (Lidar Atmospheric Sensing Experiment) for measuring water vapor and aerosols, and their effects on atmospheric processes.
• Chemical Research. Also, Ti:Sapphire laser systems are used to study chemical reactions on ultrafast time scales. Recently, devices to control and measure the spectral phase and amplitude of the ultrafast pulses have been developed in order to find applications in the field of coherent control, which has grown increasingly sophisticated in recent days.
• Biological Applications. In biology, Ti:Sapphire lasers are instrumental in multiphoton microscopy (MPM), which has developed into the leading noninvasive laboratory tool for studying underlying biological phenomena. This tool offers high-resolution three-dimensional imaging in thick tissues, including in vivo specimens.
• Other Scientific Fields. In addition to this, Ti:Sapphire lasers have been instrumental in fields such as nonlinear physics and terahertz generation. The ability of Ti:Sapphire lasers to generate ultrafast pulses and wide wavelength tunability enables unprecedented advances across a range of disciplines in science, industry, and beyond.

Ultrashort Pulse Lasers

Ultrashort pulse lasers (USP lasers) are of great value to science, and this is one area where femtoscience is already making steady and tangible achievements. The idea of an ultrashort pulse is one of the most promising and developed new concepts in femtotechnology today.

Ultrashort pulse lasers provide sufficient output power for industrial applications. These fiber lasers offer pulse lengths in the range from some 10 picoseconds to some 100 femtoseconds. Ultrashort pulse lasers can be used for laser cutting, drilling, and laser marking of surface treatment applications.

Ultrafast vs. Ultrashort Pulse Lasers

The above-mentioned fiber lasers are also known as ultrafast lasers. Ultrashort pulse lasers should not be called “ultrafast” because they are not faster (do not have a higher velocity) than longer pulses. They make it possible to investigate ultrafast processes, and can be used for fast optical data transmissions. Common current scientific laser systems based on ultrashort pulse laser technologies include Ti: Sapphire lasers and dye lasers.

Nobel Prize and Femtochemistry

The first Egyptian scientist to ever win a Nobel Prize in a science-related field is named Ahmed Hassan Zewail. He is also known as the Father of Femtochemistry. Using ultrashort laser flashes, he invented a technique to observe and describe such chemical reactions at the time intervals so short, the various transition states of matter can be peered into.

Applications of Ultrashort Pulses in Different Fields

This level of observation opened up the entire field of femtochemistry because fiber lasers are amazingly effective tools in a vast number of fields. We use fiber lasers everywhere from medical operations (in eye surgery, for instance) to manufacturing plants in high-powered laser cutters.

Cold Ablation and Industrial Breakthroughs

Lasers generate heat, but they work so quickly that the surface barely has time to warm before the job is complete. The target of the laser is vaporized before your reaction time tells you it has even begun. This is called “cold ablation”. One of the biggest challenges was converting this technique from a special advanced laboratory tool into a machine that could be used on the manufacturing floor. This conversion was made by German scientists Jens König, Stefan Nolte, and Dirk Sutter, working for the technology company Bosch. For this, they were awarded the German Future Prize 2013. Cold ablation techniques are currently being used in more manufacturing plants across the world.

Ultrashort pulse fiber lasers are one of the most practical high-power lasers and are now used as laser sources in a variety of laser applications. These fiber lasers are used as practical and functional laser light sources: they are stable, compact, and practical.

Market Growth and Key Drivers

The global fiber laser market is projected to reach $4,403 million by 2025, registering a CAGR (Compound Annual Growth Rate) of 11,9% from 2018 to 2025. Fiber lasers offer advantages such as ease of use, high reliability, maintenance-free operation, high integration capability, and high stability, which are expected to be the factors driving the market growth.

Innovation and Product Development

Fiber laser manufacturers are heavily interested in activities to enhance the range and add additional wavelengths and power levels. They thus seek ways to increase such characteristics of fiber lasers as high beam quality and to introduce new product lines. This includes UV fiber lasers, red, orange, green fiber lasers, projection, and mid-infrared fiber lasers for fine and microprocessing applications. And then to top it off, the fiber laser manufacturers are also currently developing ultrashort pulsed lasers with ultrashort pulse durations in the range of picoseconds and femtoseconds.

Fiber Laser Design and Components

The typical fiber laser is arranged in such a way that beam transfer and laser cavity are incorporated into a solitary system inside an optical fiber. It is doped with rare-earth elements such as erbium, ytterbium, neodymium, thulium, praseodymium, holmium, or dysprosium. Regular fiber lasers are optically pumped, most commonly with laser diodes, but in a few cases with other fiber lasers. The optics used in these systems are usually fiber components, with most or all the components fiber-coupled to one another. In some systems, bulk optics are used, and sometimes an internal fiber-coupling system is combined with external bulk optics.

Market Segmentation

By Fiber Laser Type

• The global fiber laser market is segmented based on various parameters such as type, application, and region. Based on fiber laser type, the market is classified into:
  infrared fiber lasers
  ultraviolet fiber lasers (UV fiber lasers)
  ultrafast fiber lasers
  visible fiber lasers

By Application

Further, based on application, the market is divided into: high power, marking, fine processing, and microprocessing

By Region

Based on region, it is analyzed across North America, Europe, Asia-Pacific, and LAMEA.

Reliability and Core Advantages

Single-mode fiber lasers possess a reliability that is unmatched by conventional solid-state and gas lasers. Selectivity of operating wavelengths, ultra-low amplitude noise, high stability, and ultra-long pump diode lifetime complete an impressive list of such fiber laser systems.

Types of Fiber Lasers

Single-Mode Fiber Lasers. Single-mode fiber lasers are typically delivered via fiber, with a core diameter of fewer than 25 microns, producing a narrow, high-intensity beam that can be focused down to a spot size as small as 20 microns. This high-intensity and a small spot are ideally suited for fine laser marking, micromachining, and cutting applications.

Multi-Mode Fiber Lasers. Multi-mode fiber lasers use fibers with core diameters greater than 25 microns, resulting in a lower intensity beam and larger focused spot sizes.

Importance of Beam Quality

Fiber lasers produce a high-quality beam, so the differences between different types of such lasers may appear small, but they are huge in processing terms. There are a number of key laser parameters that define a fiber laser processing capability, including peak power, frequency range, pulse width, and beam quality.

Processing Benefits

Beam quality may not be the most familiar parameter, but it has a significant impact and should be considered much more closely than it has been in the past. The high beam quality is a parameter that can be found in single-mode fiber lasers. A laser with better beam quality can remove material much faster, with better resolution, and improved quality.

Applications of Single-Mode Fiber Lasers

Single-mode fiber lasers have gained a sharp rise in acceptance on a large variety of welding applications, including batteries, medical assemblies, fuel cells, wire welding, and the like. The optimization of such lasers is high-speed: single-mode fiber lasers can operate in a continuous mode or a modulated mode with no spot size change over the 10%-105% dynamic operating range.

Cutting and Welding Applications

The low divergence allows for long marking distances that make focus control very forgiving and repeatable. On cutting applications, single-mode fiber lasers are utilized for precise cutting of very delicate structures such as stents, silicon wafers, surgical knives, as well as thicker materials at the higher power levels.

Marking and Micromachining

Single-mode fiber lasers provide excellent mark resolution and can achieve the mark size and quality normally associated with 532 nm lasers and 355 nm lasers. In addition to this, using single-mode fiber lasers for micromachining can be a cost-effective alternative to more costly micromachining technologies, including sinker electrical discharge machining equipment or 532- and 355-nm lasers.

History and Scientific Importance

Since its invention by Peter Moulton, the workhorse of the ultrafast laser scientific community has been the Ti:Sapphire laser. This fiber laser has been used in fundamental laboratory studies involving frequency-comb spectroscopy, the generation of coherent extreme ultraviolet light, filamentation, ultrafast laser-material interaction, and the like. It is interesting that initial work on the optical frequency comb technique, for which John Hall and Theodor Hänsch shared one half of the 2005 Nobel Prize in Physics, depended heavily on Ti:Sapphire lasers for the generation of the comb.

Properties of Titanium-Doped Sapphire

Titanium-doped sapphire (Ti:Sapphire) is the most successful solid-state laser material in the near-infrared (NIR) wavelength range due to its high saturation energy, large stimulated emission cross-section, and broad absorption gain bandwidths.

Key Features

Titanium-doped sapphire has been successfully deployed in a wide range of applications, such as high-intensity physics, frequency metrology, spectrometry, as well as pumping of tunable optical parametric oscillators. Although Ti:Sapphire has a broad absorption bandwidth, due to the relatively weak absorption peak in the blue-green range, its successful operation requires a high-power blue-green pump.

Tunability and Performance

The titanium-doped sapphire laser is a tunable laser that has excellent tunability and potential to create ultrashort pulses. Ti:Sapphire lasers also possess high laser cross sections, which, in turn, minimize their Q-switching instabilities. It emits near-infrared and red light in the range of 650-1100 nm. Pumping of Ti:Sapphire laser is carried out with another laser that has a wavelength of 514 to 532 nm, which includes Nd:YVO laser, frequency-doubled Nd:YAG laser, or argon-ion laser. It combines the excellent optical, physical, and thermal properties of sapphire, and so, it is widely used in scientific research.

Development of Ti:Sapphire Lasers

In 1982, researchers at Lincoln Laboratory operated a tunable fiber laser based on Ti: Al₂O₃ for the first time. P.E.Moulton demonstrated a widely tunable fiber laser by incorporating titanium instead of chromium as an input into sapphire.

Technological Advances

Today, dozens of tunable fiber lasers exist. A wide range of developments in Ti:Al₂O₃ laser technology then followed the advances in crystal growth that occurred during the mid-1980s. Ti:Sapphire lasers are now commercially available and are a valuable research tool found in many laboratories.

Applications of Ti:Sapphire Lasers

Nowadays, Ti:Sapphire lasers play an important role across a wide range of photonics applications, including multicolor ultrafast spectroscopy, multiphoton deep-tissue imaging, terawatt and petawatt physics, and “cold” micromachining.

Research and Space Applications

The main applications of the Titanium-doped sapphire laser are in research laboratories, particularly in spectroscopy. The large tuning range makes these fiber lasers attractive for generating tunable sub-picosecond pulses at short wavelengths. As an example, Ti:Sapphire lasers are used in the NASA project LASE (Lidar Atmospheric Sensing Experiment) for measuring water vapor and aerosols, and their effects on atmospheric processes.

Limitations and Drawbacks

Ti:Sapphire lasers are generally confined to the laboratory. These fiber lasers, and based on laser systems, are sensitive to temperature and vibration, and, therefore, they are not useful for industrial and mobile applications. Ti:Sapphire laser systems are still large, complex, and relatively expensive. The newer models require less care and feeding, but Ti:Sapphire lasers have always been somewhat difficult to keep stable under changing conditions.

Ultraviolet Fiber Lasers Overview

Ultraviolet fiber laser products are primarily intended for use in advanced studies and development in the industrial sphere. Ultraviolet fiber lasers and optical emitters are used in biotechnology and medical markets to create such special tools as sterilization and disinfectant devices. UV fiber lasers offer developers huge opportunities based on a noncontact method of producing microstructures on micro substances on different substances with a minimal effect on surrounding materials. The aforementioned fiber lasers generate light with wavelengths in the range from 150 to 400 nm.

Why UV Fiber Lasers Are Suitable for Micro-Scale Applications

What makes UV fiber lasers so applicable for micro-drilling and micro-structuring, or for marking synthetics and glass, and for creating safety features on ID or credit cards? Firstly, their short wavelength allows them to create small focused spot sizes. Secondly, short pulse width and high intensity result in the material removal (every pulse removes only a small amount of material), allowing for to production of well-defined microstructures. The beam intensity is so high that the material is removed in the vapor phase in a process called ablation. Ablation can be characterized as a process of material removal, resulting in a clean surface. And thirdly, the short wavelength is important because small focused spot sizes allow penetration into the material, where chemical and physical transitions will result in changes in the material. These changes can be observed either by the naked eye or under special lighting or with proper magnification.

Main Types of UV Fiber Lasers

Solid-state Q-switched Nd:YAG laser

Solid-state Q-switched Nd:YAG laser. A special crystal in this laser is used to change the infrared 1064 nm wavelength to the ultraviolet 353 nm wavelength. The beam shape is Gaussian, so the spot of the ultraviolet fiber laser of this type will be round, with the intensity of energy falling off gradually from the center to the edge. These ultraviolet fiber lasers are sensitive to temperature variations. They have a special standby mode where all critical components are kept at the operating temperature. Since these fiber lasers are equipped with a high repetition rate and a small focused spot, they are well-suited for machining on a micro scale.

Excimer laser

An excimer laser typically uses a combination of a noble gas and a reactive gas. The beam-generated shape isn’t round but has a rectangular shape with a more or less constant distribution of the intensity over the cross section of the beam that falls off sharply at the edges.

Metal vapor laser

A metal vapor laser. The copper vapor laser is commonly used, although vapors of several other metals are also suitable. These UV fiber lasers generate radiation at 511 nm and 578 nm wavelengths. The beam shape is Gaussian, so the metal vapor laser is appropriate for the same range of applications as the solid-state ultraviolet fiber laser.

The most important type of high-power ultraviolet laser for industrial applications is the excimer laser. Available wavelengths include 351, 308, 248, 193, and 157 nm. The largest commercially available excimer lasers generate up to 200 W stabilized average power and up to 700 mJ pulse energy at 308 nm. The main advantages of this laser are physical compactness, high reliability, and durability.

Advanced Applications of Ultraviolet Fiber Lasers

Cutting and Drilling Applications

Pulsed high-power ultraviolet fiber lasers can be used for efficient cutting and drilling of holes in a variety of materials

Fiber lasers provide high power and accuracy to these applications while maintaining low maintenance costs. Most fiber laser manufacturers provide a wide range of products that are designed according to the needs of a specific area of fiber laser applications. The ability to manufacture custom fiber laser systems is crucial for some applications that require very specific laser power, wavelength, etc.
Main areas of fiber laser cutting applications include precision engineering, including fiber laser micromachining, high precision sheet metal profiling, cutting transparent materials, marking components for traceability, etc.

UV Fiber Lasers in Flow Cytometry

Ultraviolet fiber lasers (usually 325-365 nm) remain an uncommon excitation source for cytometry.

Flow cytometry is a fundamental technique in the biomedical sciences and has helped significantly to study the immune system, cancer biology, and infectious diseases. UV lasers have become an important part of any cytometer setup due to recent developments in dyes used for tagging cells. Flow cytometry is the process of detecting cells with the help of molecular fluorescent tags. Cells are introduced into the laser beam in a hydrodynamically focused liquid stream in the process. A flow cytometer operates in the following way: the cells are introduced into a laser beam with a nozzle or enclosed quartz flow cell; fluorescent tags get excited, and signal collection optics collect the signals produced by the tags. The signals are steered to PMTs using dichroic mirrors and narrow bandpass filters. The tags used in cytometry are able to detect different types of cells in complex mixtures, as well as different characteristics of single cells.
Modern flow cytometers utilize solid-state lasers with wavelengths from the ultraviolet to the long red. In order to excite a wide variety of fluorescent tags, multiple single-wavelength lasers can be used to detect the cells. An average number of cell characteristics that can be detected in a modern cytometer is 20, which is significant when compared to earlier instruments. Modern UV lasers, including UV fiber lasers, are a cost-efficient replacement for traditional laser sources in flow cytometry; they are smaller and more compact.

Microlithography Applications

Continuous wave UV fiber lasers are required for microlithography (for instance, in the context of semiconductor chip manufacturing).

The clear target of microlithography is to strive for even smaller systems. Huge HeCd lasers and gas lasers have already been replaced by modern compact violet and ultraviolet diode lasers in modern microlithographic systems. The excellent performance of ultraviolet lasers allows a lower cost of laser ownership; the qualities of generation have to be carried out by external modulators. Ultraviolet diode lasers can be pulsed at high frequencies. In addition to this, using pulse width modulation, different levels of imaging (gray-scaling) can be obtained.

Fabricating Fiber Bragg Gratings

Pulsed and CW UV fiber lasers are irreplaceable for fabricating fiber Bragg gratings.

The most trivial method for FBG fabrication is to expose a photosensitive fiber to an interference fringe pattern in UV light. This is actually accomplished by directing the output of an excimer (UV) laser through a phase mask. The phase mask diffracts the incident laser light into various orders, which overlap and optically interfere with each other in the mask vicinity. This process is conceptually straightforward, but there are several insurmountable barriers to overcome. Firstly, the cost of the excimer laser as well as the phase mask. Secondly, there is a need for holding and positioning all the components in such a way that a grating having the right spacing and index variation characteristics can be produced at exactly the correct place along the optical fiber. The system, among other things, must have some way to accommodate the batch-to-batch variations in the index of the fiber used if the goal is to produce a large number of FBGs with each having consistent characteristics.

Medical Applications

UV and even deep-UV lasers are required in refractive laser eye surgery of the cornea and in other medical applications.

Ultraviolet fiber lasers are most commonly used to correct myopia (nearsightedness), but can also be used to correct hyperopia (farsightedness) and astigmatism. The ultraviolet excimer laser alters the refractive state of the eye by removing tissue from the anterior cornea through a process known as “photoablative decomposition”. This process uses ultraviolet energy from the excimer laser to disrupt chemical bonds in the cornea without causing any thermal damage to surrounding tissue. The modified anterior corneal surface enables light to be focused on the retina, thereby reducing or eliminating the dependence on glasses and contact lenses.
etc.

An Extraordinary Laser of a New Generation

According to the forecasts, UV fiber lasers will be widely used in an expanding range of applications with their recent improvements in performance, cost of ownership, and increasing reliability.

Optromix Ultraviolet Fiber Laser Development

Optromix scientists developed the super-technologically advanced ultraviolet laser based on a single-frequency fiber laser with a wavelength of 1030 nm. A ytterbium-doped DFB (distributed feedback) fiber laser was used as a seed laser. The radiation of the DFB fiber laser was amplified in a few fiber amplifiers to 10 W. With this power, there was achieved 1,5 W at 515 nm. The second harmonic 515 nm was obtained with PPSLT (Periodically Poled Stoichiometric Lithium Tantalate) crystal, which was converted to the fourth harmonic 257,5 nm in the external cavity. This power level was enough to obtain 100 mW in the UV region of the spectrum. On the basis of these results, the compact and energy-efficient UV source was developed, which does not require water cooling.
The creation of fiber Bragg gratings (FBG) is an inescapable part of modern fiber optic technology and, specifically, the technology that aims to create fiber lasers. The process of Bragg grating writing is effective when using ultraviolet (UV) radiation. Different types of lasers can be the sources of ultraviolet radiation. Nowadays, the best characteristics for writing FBG are the length of coherence, positive stability, and beam quality of germane-silicate optical fibers. The frequency doubling of the continuous wave argon laser contributes to meeting these characteristics at 244 nm.

Comparison with Argon and Excimer Lasers

The argon laser is a complex system that consists of an evacuated laser tube, a power source, and a pump that is necessary for circulating the cooling liquid in the laser tube. The basic operating costs are related to high electricity and water bills. Additionally, these fiber lasers need regular repair and replacement of the vacuum gas discharge tube. Argon lasers need permanent repair and maintenance with the constant help of highly qualified specialists.
The pulsed excimer lasers at 248 nm are the most common and relatively cheap. These excimer fiber lasers are more effective than argon lasers, but they have a much worse beam quality and a pulsed generation mode. These parameters limit the possibilities for FBG writing for the excimer lasers.
The above-mentioned ytterbium-doped fiber laser with the 4th harmonic generation in the BBO crystal is an alternative for FBG writing. In addition to this, the Optromix ytterbium-doped ultraviolet fiber laser has several advantages in comparison with the argon laser.

Advantages of Optromix Ytterbium-doped UV Fiber Laser

• Optromix laser is smaller and lighter than the conventional argon laser
• It is easier to manage and maintain
• Optromix laser has low energy consumption
• Optromix laser does not need water cooling
• Optromix laser is relatively inexpensive