Category: Fiber Laser Technology

Fiber laser modules in various fields of medicine

Since the creation of the first laser modules, specialists have conducted extensive research on the effects of laser radiation on biological tissues. Fiber lasers have contributed to developing various treatment methods for different diseases.

The main advantages of fiber laser modules in medicine

Depending on radiation power, laser modules can be used for heating, cutting, or coagulation of biological tissue.

Key benefits

Advantages of medical instruments with fiber lasers compared to traditional equipment:

fiber lasers allow non-invasive or minimally invasive cuts;
high temperatures sterilize wounds, reducing infection risk;
minimal wound swelling;
reduced postoperative complications;
shorter recovery period.

Today, fiber lasers are applied in otorhinolaryngology, vascular disease treatment, cardiac surgery, orthopedics, traumatology, neurosurgery, gynecology, proctology, dentistry, and other fields.

Fiber lasers’ radiation levels and applications

Different effects of fiber laser radiation on biological tissues depend on the wavelength. This is determined by the absorption coefficient, scattering coefficient, and moisture content. Absorption affects penetration depth. Water and hemoglobin are the main absorbers in biological tissues.

Common radiation ranges

Common radiation ranges used in medicine:

0.94–0.98 µm radiation provides an optimal balance of cutting and coagulation in surgery;
1.06 μm radiation is used for controlled volumetric tissue heating;
1.4–1.8 μm wavelength is mainly for water heating to 100 °C and evaporation;
1.8–2.1 μm wavelength, like CO2 lasers, offers good cutting, minimal thermal damage, and effective coagulation;
Lasers with wavelengths >2 μm are widely used. Wavelengths between 2.05–2.3 µm operate in the atmospheric transmission window and are used where eye safety is critical.

Thulium-doped fiber lasers provide 1900–2000 nm wavelengths, matching absorption peaks in biological tissues:

Fiber lasers up to 10 W are used in cosmetology and dentistry;
40 W lasers are applied in gynecology, proctology, and vascular treatments;
50–120 W fiber lasers are used in urology for transurethral prostate vaporization.

Features of fiber lasers’ use in medicine

Fiber lasers are used in many technical and scientific fields. They are compact, resistant to vibrations and electromagnetic interference, and can be equipped with various commercially available components.

Individual approach and surgical applications

Each pathology requires an individual approach. Specialists set the appropriate laser modes for each medical field. Fiber lasers help reduce surgical injuries and shorten recovery time. Fiber lasers are important in modern endoscopic surgery and are fully compatible with surgical endoscopes, enabling minimally invasive procedures.

Today, fiber laser modules are widely used in biology and medicine. Future research will focus on laser effects on natural and artificial tissues and on optimizing laser parameters.

Novel highest efficiency and power fiber laser: the advanced technology

History and Applications of Fiber Lasers

The first fiber laser was demonstrated over 50 years ago by E. Snitzer in a Neodymium doped fiber. Today, fiber lasers find many applications in different spheres f.e medical diagnostics, laser material processing, imaging, metrology, and scientific research. It is interesting to note how many advantages have fiber optics laser technology.

Advantages of Fiber Laser Technology

The fiber laser is the highest efficiency and power laser that can be used in different spheres. Fiber lasers are compact and rugged, don’t go out of alignment, and easily spend thermal energy.

Structure of Fiber Lasers

The fiber laser’s waveguides are unique. The inner active core is doped with a rare earth – like ytterbium, erbium, thulium and defines oscillation wavelength. It is surrounded by Fiber Bragg Gratings, which confines the pump light and couples it into the active core.

High Beam Quality and Precision

Ultra-short pulse lasers can shape very precise microstructures and fabricate novel laser sources for industry. Fiber lasers support high beam quality at all the entire power range. In most common laser solutions, the beam quality is sensitive to output power. In fiber lasers, the output beam is virtually non-divergent over a wide power range. So, the beam can be concentrated to achieve high levels of precision, increased power densities and longer distances over which processing can be accomplished.

Efficiency and Design Benefits

Usage of a fiber as a laser active medium allows prolonging interaction distance, which works well for diode-pumping. This geometry leads to high photon conversion efficiency, as well as a rugged and compact design. When novel fiber sources are joined together, there are no discrete optics to adjust or to get out of alignment.

Adaptability and Variations of Fiber Lasers

The highest efficiency laser is highly adaptable. It can be adjusted to do anything from welding heavy sheets of metal to producing femtosecond pulses. Many variations exist on the fiber-laser theme. Fiber amplifiers provide single-pass amplification; they’re used in telecommunications because they can intensify many wavelengths in the meantime. Another example is fiber-amplified spontaneous-emission sources, in which the induced emission is suppressed. The Raman fiber laser is the another pattern, which is based on Raman gain that essentially Raman-shifts the wavelength. This is an application that’s not be practiced on a wide scale, but it certainly finds an application in research.
The market for the highest efficiency lasers is rapidly increased. Also seeing the substitution of non-fiber lasers with fiber lasers. The area of application fiber lasers now is an integral part of many photonic applications including biomedicine, material processing, astronomy and fundamental research. Nowadays, continuous wave fiber lasers with output powers above 1 kW become available. Fiber laser development still continues to be an active research field.

Concept of Supersymmetry in Fiber Laser Technology

Development Challenges of Microlasers

Ring microlasers are potential light sources for photonic applications, but several challenges remain. For example, connecting multiple fiber lasers into a set may produce unwanted additional modes. Modern fiber laser technology enables the creation of chip-sized single-mode lasers.

Developing a single-mode chip-sized laser requires making fiber lasers stronger, smaller, and more stable. A research team from the USA recently designed two-dimensional arrays of microlasers with single-mode stability, achieving higher power density than previously reported.

Coherence and Stability Requirements

The fiber lasers must be coherent and stable to preserve data processed by photonic devices. Single-mode lasers provide optimal coherence, but their combined output is weaker than that of multimode lasers. To produce high-power multimode output, multiple single-mode lasers must be combined; however, mode competition reduces the coherence of the fiber laser array.

Supersymmetry in Fiber Laser Arrays

Achieving single-mode operation is critical because the brightness of a fiber laser array increases with the number of lasers when they operate synchronously in a single supermode. Researchers concluded that single-mode operation can be realized by introducing a “superpartner” based on the concept of supersymmetry.

Two-Dimensional Microlaser Arrays

According to the research team, previous studies using the superpartner fiber laser array principle were limited to one dimension. The current system demonstrates a two-dimensional array with five rows and five columns of microlasers. The team predicts that higher power scaling can be achieved using the same principle for larger arrays.

Applications of Single-Mode Lasers

This approach can also be applied to vortex lasers, which allow precise control of the laser beam and its spiral motion. Controlling laser beams in this way may enable encoding fiber laser systems at higher densities.

Single-mode lasers have a wide range of applications, from optical sensing to optical communications. This research contributes to the development of more efficient laser modules.

High-performing laser: Single-frequency laser system for optical tweezers

Principles of Optical Tweezers

The principle of the optical tweezers is based on the fact that light beam has a pulse and when it its direction is changing it creates power.

Concept of Pulse in Mechanics

The concept of a pulse comes from mechanics, where the body mass multiplied to its speed stand for the pulse. Speed is a vector that describes the magnitude and the direction. Hence, object motion happens under the influence of power, and the direction of the speed is connected to the shift of the power direction.

Light Interaction with Particles

When a photon is projected on a non-transparent surface, then the pulse is just the light pressuring on this surface. However, when pointing the high-performing laser on the transparent particle, the light beam is diffracted – the direction of the light vector and as a result of the photons is changing. By analogy with the mechanics it is fair to say that the power shift will affect the particle in a way that it will move towards the highest insensitivity of the laser beam.

Gaussian Beam Trapping

Insensitivity of the high-performing laser beam is the highest at the core and fades on the edges. The law of the insensitivity shift corresponds to the Gaussian distribution. That is why the particle stays at the core of the beam, and when the beam is focused it is “sucked in” by the beam and becomes “trapped”. This kind of three-dimension trap needs power of several mV.

Manipulating Particles with Optical Tweezers

By moving the focus it is possible to move the particles, creating different structures with them. Using the optical tweezers the scientists can trap a chromosome and then cut it for further research. Single-frequency laser system with 1064 nm wavelength is a good solution for trapping, and for cutting a green laser with 532 nm wavelength. Optical tweezers is the best tool for these kinds of manipulations; however, it has certain weaknesses.
First of all, the more the beam is focused the faster it radiates. This means that the power holding the particle fades very fast the further away it is from the trapping zone, and at the distance of several dozens of microns from the focus the power is insufficient to trap it again. Single beam trap is only useful to trap a single particle located in the focus area.
Second of all, laser beam changes after it reaches the object because of the diffraction, reflection or absorption. This also limits the distance of optical tweezers.
The more the beam radiates the harder it is to focus the optical system, and it is impossible to obtain the perfect parallel beam because of the diffraction. However, there is a type of light beams that are free from diffraction, they are called Bessel’s beams.
Regular Gauss beams are converted into Bessel beams with so called axion conical lens that focuses the High power single-frequency laser beam not into a dot, but into a line. Optical tweezers that use Bessel’s beam can trap particles located on a distance of 3 mm from each other. Single-frequency laser system with 1064 nm wavelength was used.
Optical tweezers allow measuring different mechanical properties of the DNA molecules. It is currently used to transplant genes into cells, and also for invitro fertilization.

Utilizing Nd:YAG Q-switched Lasers in Solid-State Laser Technology

Introduction to Q-Switching

Q-switching technique is usually utilized in solid-state laser technology to generate nanosecond high energy pulses. It creates short pulses through regulating cavity losses. Q factor (quality factor) is a definition of an oscillation damping strength measurement.

Types of Q-Switching

There are two types of q-switching: passive and active.

Active Q-Switching

Active q-switching technique uses an electrically controlled modulator (acousto-optic or electro-optic). It is applied to control optical losses which are high initially, but in the process of switching they are lowered abruptly. Pump phase and the gain-medium upper-state lifetime should be roughly the same to avoid losing energy in spontaneous emissions. Energy loss through spontaneous emissions becomes significant when laser gain is high. However, it is not the biggest concern when it comes to bulk lasers. A bigger issue is parasitic lasing because of unwanted reflections or q-switch. To avert the lasing a modulator should have a high pump phase when performing power losses.
It is possible to design smaller mode area lasers when the energy per pulse and energy stored are lowered due to high pulse repetition rates (10 kHz, 100 kHz or more). However, high repetition rates create another issue – collecting enough laser gain even when stored energy is low, because when the gain is low pulses become longer. Even in case of high average powers it can still be problematic, because it may need bigger beam areas. That is why it is better to select a crystal providing a higher laser gain, for example, Nd:YVO4.

Passive Q-Switching

Passive q-switching technique uses a saturable absorber instead of an electrical modulator. There is a high optical loss when it is in the unsaturated state. To start the lasing a laser gain has to reduce that loss. When the emission increases, it saturates losses, and the laser power grows fast, which leads to the gain saturation.
It may give an impression that it is poor because of the absorption; however this is not the case. Just a little portion of energy is required for an absorber transparency, when the laser gain medium saturation energy is higher than the absorber energy. One of the most common crystals used in this case is Nd:YAG.
The pumping in a passive q-switched laser continues up to a moment when a pulse build up begins. This process begins when there is enough energy stored in the gain medium. The main difference between passive and active q-switching technique is that in case of a passive one the pumping power change does not affect the energy pulse, it will only effect the timing. In active q-switching technique both will be affected, the energy pulse and timing.

Thulium Fiber Laser for LIDAR and Gas Sensing Systems

Introduction to Thulium Fiber Lasers

Ultra-short pulsed femto- and picosecond lasers are in high demand today. Thulium-doped lasers, definitely, stand out because of their capability to generate emissions in a wide range. Thulium Fiber Laser has unique qualities which make it perfect for a lot of different applications, namely, medicine, spectroscopy, laser ranging and micromachining of transparent materials, in particular, semiconductors and laser for LIDAR. Presently, they are the most effective sources of a single-mode emission with the wavelength in 2 µ range.

Medical and Biological Applications

Thulium Fiber Laser water absorption properties are outstanding. The main constituent of any biological tissues is water, which is why strong water absorption quality of thulium laser allows significant heating of small areas. In other words, cutting biological tissues becomes extra precise. All of the above make Thulium Fiber Laser irreplaceable when it comes to performing surgical procedures.

Advantages for Free-Space and Sensing Applications

Thulium lasers compared to traditional optimal cost-efficient laser systems that operate at shorter wavelengths have undeniable advantages when using for free space applications. It gives them a high commercial value, especially as laser for LIDAR and gas sensing systems, optical communication applications and pumping lasers for the mid infra-red spectrum.

Host Materials and Laser Types

Thulium doped lasers are released either in fiber or crystal host materials. Depending on the host material the wavelength range spreads from 1840 nm to 2100 nm. Thulium fiber can either be a q-switched laser or continuous wave laser, and both develop significantly a high average power. On the other hand, thulium doped crystals have a broad emission spectrum, which allows a large wavelength tuning range. Thulium doped crystals are of really good quality with a few imperfections and defects. YAG and YFL crystals reveal the best quality nowadays; however, they are not the best choices because of their thermal conductivity and emission cross section. There is definitely a room for improvement, and further research has to be done to enhance their performance.
Despite the fact that there are so many different applications in a lot of industries only few laser technology providers can deliver this type of laser at the moment. Currently, Optromix is developing its own thulium laser and will release it shortly for commercial use (e.g. laser for LIDAR).

Powerful laser equipment: Nd:YLF Laser or Nd:YAG Laser

Introduction to Nd:YLF Laser

Nd:YLF laser active elements are made of yttrium lithium fluoride (YLiF4) crystal. YLF stands for Yttrium Lithium Fluoride. Usually neodymium-doped YLF crystal is used for YLF laser equipment; however, it can also be doped with rare earth elements, such as ytterbium (Yb), erbium (Er), thulium (Tm), holmium (Ho) or praseodymium (Pr).

Crystal Composition and Properties

Yttrium ions in YLF crystal may be substituted with laser-active rare earth ions, because of its similar size, without distorting the structure of crystal lattice. In neodymium-doped YLF crystal its (Nd3+) concentration is usually up to 1% of its total weight.

Birefringence and Polarization

YLF crystal has a natural strong birefringence, which removes thermal polarization losses. Besides the emission wavelength and the gain of the Nd:YLF crystal waves are polarization-dependent, there is a stronger wave of 1047 nm and a weaker one of 1047 nm. It makes Nd:YLF crystal better for a less powerful laser equipment that require extra precision.

Matching Wavelengths for Amplifiers

1053 nm wavelength matches the maximum for loop gain of phosphate laser glass, that contains neodymium ions, that is why Nd:YLF lasers are often used as a master oscillator and preamplifier for the subsequent stages of the neodymium phosphate glass amplifier.
Diode-pumping and lamp-pumping is possible for Nd:YLF laser. It has lower thermal conductivity in comparison with Nd:YAG laser, but its thermal distortions are weaker, which leads to a better beam quality and worse fracture resistance, hence it limits the output power in the laser equipment.

Nd:YAG is an Optimal Cost-Efficient Laser for Scientific Laser Systems

Introduction to Nd:YAG Lasers

YAG stands for yttrium aluminum garnet, which is a synthetic crystal. Nd:YAG is an artificial cubic garnet crystal. YAG crystals were created shortly after ruby laser discovery. They have high gain and other unique properties which make them universal for a lot of different applications. YAG crystals increase the stability of the source, its efficiency and lifespan, reduce size and power consumption.

Limitations and Operating Properties

There are certain limitations connected with the high gain and the safety of the operating fluence. Mode-lock property creates pulses of very different widths – nanosecond to picoseconds, which enables it to make wide-ranging peak power for various applications.

Technical Characteristics of Nd:YAG Lasers

YAG laser is a solid state diode pumped laser, its beam is in mid infra-red range and its wavelength is 1064 nm. Nd:YAG is an outstanding solution for scientific laser systems because it can reach extremely high powers in a pulsed mode, which is used in the oscillators to produce series of very short pulses to perform research with femtosecond time resolution.
Nd:YAG laser may be used with a frequency doubler, in this case its wavelength is 532 nm and its output power is lower.

Applications of Nd:YAG Lasers

In terms of applications, yag laser systems are very versatile. It has been widely used in the military, for example, for rangefinding or for target designation.
On the other hand, as mentioned before its pulse width and high power, it is extremely useful for scientific purposes, or as a pumping source for other lasers.
Medicine is another field where Nd:YAG is frequently used, namely dermatology and ophthalmology. Commercial purposes include applications such as ablation, spectroscopy, marking, nondestructive testing and others. Moreover, it is an optimal cost-efficient laser.
Key feature of the YAG lasers is its resilience to different environmental conditions; hence it suits perfectly well for remote sensing, bathymetry, gated imaging illumination, atmospheric and ocean studies, etc.
Other lasers or nonphotonic techniques may be used for most of the applications mentioned above, for example, diode or CO2 lasers. Nd:YAG allows to perform a broad range of applications, because of its one-of-a-kind properties, and also, not many lasers have an ability to function efficiently with diode pumping and to switch between pulsed or CW mode.

Advanced laser systems, technology and equipment for LIDAR

Introduction to LIDAR Technology

LIDAR (light detection and ranging) is a laser technology used for optical remote sensing which allows one to analyze scattered light properties in order to obtain certain information about a distant object.

How LIDAR Systems Work

These advanced laser systems are often used, for example, to collect precise information about Earth surface and its characteristics. The sensor sends out a pulse of light to travel to an object, it reflects off the object and travels back. When the light clashes into an object, the sensor detects the reflected pulse. Then it measures the time necessary for the reflected pulse to return. The light pulse travels with the speed of light which is known and constant; hence, the time is easily converted into distance or as it is called – the range. The information on the position and angle of the laser equipment allows calculating exact coordinates of the object reflected.

Applications of LIDAR Technology

LIDAR technology can be applied in a lot of different areas, from geographical mapping to robotics due to its high configuration capabilities and wavelengths.
There are different types of LIDARs: rangefinder, DIAL and Doppler.
Rangefinders measure a distance between a sensor and a solid object.
DIAL (differential absorption) measures chemical concentrations in the atmosphere (ozone, water vapor, pollution). It emits pulses with two different wavelengths which are set in a specific way, so that a molecule can absorb one of them, but the other can’t. This way the molecule concentration is deduced.
Doppler technique measures an object velocity. When a light pulse travels to a moving object, its wavelength changes a little, and it is called Doppler shift. When the object is moving away from the sensor, the reflected wavelength will be longer, and when the object is moving towards the sensor, the reflected wavelength will be shorter.

Advantages of high beam quality lasers

Beam quality can sometimes be an overlooked quality of a laser; however, this characteristic provides several advantages, such as faster and finer-feature machining, better process quality and an increased depth of focus. High beam quality laser has strong focusing capabilities and allows for a longer working distance which means that these types of lasers can be used in rough working environments without damaging the optics and the laser itself.
Beam quality is defined by M2, which represents a ratio of the beam of the laser and the perfect beam; consequently, the closer M2 is to 1, the better the quality of the laser beam. High beam quality lasers have M2 of less than 1,3. Due to the aforementioned reasons, lasers with high beam quality are very precise as they can produce an optical spot down to 20 microns. The best beam quality is produced by single mode lasers with M2 values around 1,1 – 1,2.
High-quality beam lasers prove to be useful in a variety of different applications:

Micro machining

The fine-tune nature of high-quality beam lasers is used to conduct machining operations on a small scale – drilling, slotting, cutting, etc. Laser surface engraving, for instance, is a process of emergence of small cracks in a material (around 100μm in size) under the pressure of melting and evaporation that occurs when a laser beam hits a surface.

Surface scrubbing

High beam quality provides consistency in scrubbing quality and high tolerance to defocusing during removal of thin materials from other films or a substrate. The low M2 does not result in quality degradation when the laser defocuses. The defocusing of a system occurs due to an uneven working surface, and lasers with high M2 can potentially result in a decreased production yield.

Removal of skin pigment and dye

High beam quality lasers are used to remove skin pigmentation and tattoos.
Generally, gas lasers, like CO2 lasers, exhibit a high beam quality.