Ultraviolet Fiber Lasers: New Types, Features Expand Applications, and Future Opportunities

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 like sterilization and dezinfectant devices. UV fiber lasers offer to 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.

Ultraviolet fiber lasers are well suited 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) allow to produce 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 the material removal, the end result of which is 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 of the material. Such changes can be observed either by the naked eye or under the special light or proper magnification.

There are three main types of UV fiber lasers:

  1. 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. Such fiber lasers have a special standby condition where all critical components are kept at the operation temperature. Due to the fact that such fiber lasers are equipped with the high repetition rate and the small focused spot they are well suited for machining on a micro scale.
  2. 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.
  3. A metal vapor laser. The copper vapor laser is commonly used although vapors of several other metals also are suitable. Such UV fiber lasers generate radiation at 511 nm and 578 nm wavelength. The beam shape is Gaussian so the metal vapor laser is appropriate for the same range of applications like the solid-state ultraviolet fiber laser.

The most important type of high power ultraviolet laser for industrial application 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 a physical compactness, high reliability, and durability.

 

Advanced Applications of Ultraviolet Fiber Lasers

Ultraviolet fiber lasers have already found various applications at the present time:

  • 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.

 

  • 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 immune system, cancer biology, and infectious disease. 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 amount 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.

 

  • 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 lasers ownership, qualities of generation has 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.

  • 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, 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.

  • 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 That Will Solve a Number of Problems of the Laser World

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 with their increasing reliability.

Optromix scientists developed the super-technologically advanced ultraviolet laser based on single frequency fiber laser with wavelength 1030 nm. An ytterbium-doped DFB (distributed feedback) fiber laser was used as a seed laser. The radiation of the DFB fiber laser was amplified in few fiber amplifiers to 10 W. With this power there was achieved 1,5 W at 515 nm. The second harmonic 515 mn 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 UV region of spectra. 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 aimed 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 germanosilicate optical fibers. The frequency doubling of the continuous wave argon laser contributes to meeting these characteristics at 244 nm.

In itself, the argon laser is a complex system which consists of an evacuated laser tube, a power source, and a pump that is necessary for circulating of the cooling liquid in the laser tube. The basic operating costs are related to high electricity and water bills. Additionally, such fiber lasers need regular repair and replacement of a vacuum gas discharge tube. Argon lasers need permanent repair and maintenance with the constant help of highly qualified specialists.

In this connection, it is necessary to emphasize that the pulsed excimer lasers at 248 nm are most common and relatively cheap. Such 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, Optromix ytterbium-doped ultraviolet fiber laser has several advantages in comparison with the argon 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 a water cooling
  • Optromix laser is relatively inexpensive

Optromix Inc., headquartered in Cambridge, MA, USA, is a manufacturer of laser technologies, optical fiber sensors, and optical monitoring systems.

We develop and manufacture a broad variety of fiber lasers, СО 2 lasers, Ti: sapphire lasers, dye lasers, and excimer lasers. We offer simple erbium laser and ytterbium laser products, as well as sophisticated laser systems with unique characteristics, based on the client’s inquiry.

We manufacture lasers using our own technologies based on the advanced research work and patents of international R&D team. Laser processes are high quality, high precision, easily-automated manufacturing solutions that provide repeatability and flexibility.

If you are interested in fiber laser systems, please contact us at info@optromix.com

 

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