Category: Custom Laser Solutions

Applications and Capabilities of Green Fiber Lasers

A large-scale green fiber laser production allows us to serve new markets and applications in increasing number. Now it’s possible to visually trace high-energy particle flows in gases and to further characterize them with the help of powerful green lasers. Green fiber lasers can also be used for photoacoustic measurements of hemoglobin.

Pulsed Green Fiber Lasers

Today, many scientists believe that pulsed green fiber lasers are much more productive and compact than other available lasers. The pulsed green fiber lasers supply a high peak power with an average output of 10W, which can be scaled. Higher powers of Optromix’s lasers, it should be noted, are in the works. Such lasers possess a pulse duration of just 1 ns and a frequency of 50 to 600 kHz also includes also featuring M2 of less than 1.2, a collimator, and a narrow line width at 532 nm.

Continuous Wave (CW) Green Fiber Lasers

In addition to pulsed green fiber lasers, there are continuous wave (CW) lasers. The CW lasers emit a continuous or, in other words, permanent laser beam with a controlled heat output. By dint of the CW lasers, it becomes possible to control the heat output, as beam duration or intensity. The CW lasers, especially, are typical tools in semiconductor research, because through their use, laser beams can be directed into a port in the spectrometer directly onto the sample. Such CW lasers are available for use with a wide diversity of fiber terminations, collimation optics, and processing heads.

Next generation of laser technology

Polariton laser systems are garnering significant interest as the next generation of laser technology because they can operate at extremely low power, even though advances in laser modules are constrained by challenges in maintaining exciton thermal stability, especially in nanoscale devices. A team of researchers from Pennsylvania presented a polariton nanolaser system operating at room temperature. They confirm that this laser module can help in numerous related research areas, for example, the laser device can be applied in polariton physics at the nanoscale as well as in quantum information systems.

Principle of operation of polariton lasers

The principle of the laser module operation is based on the material excitation by producing Coulomb-bound states of electron-hole pairs (excitons) that strongly interact with photons. A macroscopic quantum state of exciton-polaritons is created and takes advantage of both the light and the matter, forming very energy-efficient coherent light sources.

Formation of exciton-polaritons

To address the existing issue, the researchers utilized a “quantum well,” a term that refers to a region where electrons can move freely. The quantum well was installed on the sidewall of the nanostructure semiconductor laser system. The team succeeded in supporting thermally stable excitons in the laser module even at room temperature; in the contrary cases, they are stable only at very low temperatures.

The quantum well structure used in the mentioned laser system offers new benefits, such as the formation of more efficient and stable exciton-polariton states than before, due to strengthening the exciton and light coupling inside the nanostructure semiconductor laser.

Efficiency and performance of the nano-laser

This development allows producing polariton nano-laser systems that demonstrate stable operation at room temperature; their power consumption (power density of 180 to 360 mW/cm2 for the acquisition time of 10 s) is considered to be only 1/10th of conventional nanostructure laser modules.

Potential applications and advantages

The research team also claims that the novel nanostructure semiconductor laser system enables increasing the exciton properties and consequently the exciton-polaritons. Finally, it is possible to design the polariton nano-laser system that is able to operate at room temperature conditions with the help of this laser technology. The developed nano-laser device is highly promising because it makes a contribution to the creation of a platform to study the physical phenomena related to the exciton-polaritons in room temperature environment.

New development of eye-safe fiber lasers

New highly efficient fiber lasers that are safe for the eyes have been developed by researchers from the U.S. Naval Research Laboratory. Based on the use of nanotechnology, the researchers include rare-earth ions of holmium in the core of the laser system’s silica fiber. This laser technology allows achieving an 85% level of efficiency with a fiber laser operating at a wavelength of 2 µm that is regarded as safer for the human eyes than a conventional 1 µm wavelength laser system.

Nanopowder doping process

The particle size of the nanopowder dopant is generally less than 20 nm. This is the reason why it was necessary to produce an appropriate crystal environment for the rare-earth ions in a fiber laser. The solution to the problem is the application of “clever” chemistry that dissolved holmium in a nanopowder of lutetia or lanthanum oxide or lanthanum fluoride.

Challenges of doping nanopowders into silica fiber

The researchers also face the challenge of successfully dope these nanopowders into the silica fiber in quantities that would be appropriate to reach laser system generation. The use of a room-sized, glass-working lathe enables cleaning the glass that is the future optical fiber with fluorine gases, then the American researchers molded the glass with a blow torch, and infused it with the nanoparticle slurry.

Creation of optical preforms

A rare-earth-ion-doped, 1-in. diameter glass rod or simply optical preform has to be then softened with a furnace and elongated to create an optical fiber about as thin as a human hair for its future application in the fiber laser system. The advantages of the novel fiber laser include not only improved eye safety, but the nanoparticle doping in the laser system also defends the rare earth ions from the silica, as well as separates them (the ions) from each other, thus saving the light output produced by a laser beam.

Eye safety advantages of 2 µm fiber lasers

The scattered light from the path of a 100-kW fiber laser operating at 1 µm is able to provoke severe damage to the retina, leading to blindness, while the laser system with wavelengths beyond 1.4 µm (like this fiber laser system) reduces the danger from scattered light.

Potential applications of eye-safe fiber lasers

The potential applications of the new specialty fiber lasers include:

• high-powered laser systems; 
• amplifiers for defense, telecommunications, and even welding;
• laser-cutting. 

The presented laser technology is considered to be highly prospective and commercially effective because the process of powder production and its installation into the optical fiber has a low cost and resembles the development of a telecom fiber.

Pulse (TOF) laser measurement technology

There is a common opinion that laser technology allows measuring the distance only by directly measuring the “flight” time of the laser beam pulse to the reflecting object and vice versa. This laser technique (called pulse or time-of-flight or TOF) is used mainly in cases where the distances to the desired object are sufficiently large (> 100m). Since the speed of the light emitted by the laser beam is pretty high, it is quite difficult to measure the TOF of light, and therefore the distance, with high accuracy in a single laser beam pulse. Light travels 1 meter in about 3.3 ns, so the accuracy of measuring time should be nanoseconds, although the accuracy of measuring the distance will still be tens of centimeters. Specialized microchips are used to measure time intervals with such precision.

Phase laser measurement technology

There are other laser technologies for changing the distance, one of them is a phase one. Compared to the previous one, in this technique, the laser system operates continuously, but the laser beam light is amplitude-modulated by a signal of a certain frequency (usually these frequencies are less than 500 MHz). The laser wavelength remains unchanged (usually 500 — 1100 nm laser system is applied).
The light reflected from the object is received by the photodetector, and its phase is compared with the phase of the reference signal from the laser system. A delay during the wave spread causes a phase shift, which is measured by the range measuring system. This operates only if the distance to the object is less than half the wavelength of the modulating signal.

Accuracy and limitations of phase measurement

If the modulation frequency is 10 MHz, then the measured distance can achieve up to 15 meters, and when the distance changes from 0 to 15 meters, the phase difference will change from 0 to 360 degrees. A change in the phase shift by 1 degree, in this case, corresponds to the object displacement by approximately 4 cm.
If this distance is exceeded, an ambiguity arises; to be precise, it is impossible to determine how many wave periods fit in the measured distance. The modulation frequency of the laser system is switched to solve the problem.
The simplest case is the use of two frequencies; the distance to the object is determined at low frequency (but the maximum distance is still limited), the distance with the required accuracy is determined at high one, with the same accuracy of phase shift measurement; the accuracy of distance measurement will be much higher using high frequency.
Since there are relatively simple ways to measure the phase shift with high accuracy, the accuracy of distance measurement in such laser system rangefinders can reach up to 0.5 mm. It is the phase laser technique that is used in range measuring systems that require high measurement accuracy – geodetic range finders, laser system roulettes, scanning range finders mounted on robots.
The presented laser technology also has drawbacks that include the power of the laser beam produced by a constantly working laser system is noticeably lower than that of a pulsed laser, which does not allow the use of phase range finders for measuring large distances. Besides, the phase measurement with the required accuracy can take a certain time, which limits the performance of the laser device.
The most important process in such a laser system rangefinder is the measurement of the signal phase difference, which determines the accuracy of distance measurement. There are various laser techniques for measuring the phase difference, both analog and digital. Analog methods are much easier; digital ones give greater accuracy. In this case, it is more difficult to measure the phase difference of high-frequency signals by digital methods – the time delay between the signals is measured in nanoseconds (this delay occurs as in the pulse laser system range finder).

Heterodyne conversion and synchronous detection

The heterodyne signal conversion is used to simplify the task – the laser beam signals from the photodetector and laser system are separately mixed with a signal of close frequency, which is formed by an additional generator, a heterodyne. The frequencies of the modulating signal and the heterodyne differ by kilohertz or units of megahertz. The signals of the difference frequency are distinguished from the received laser beam signals using the low-pass filter. The phase difference between the signals in this transformation does not change. The phase difference of the received low-frequency signals is much easier to measure after that by digital laser technique – it is possible to easily digitize the signals with a low-speed ADC, or measure the delay between the laser beam signals (it decreases noticeably with decreasing frequency) using the laser device. Both methods are quite simple to implement on the microcontroller.
There is another way to measure the phase difference — digital synchronous detection. If the frequency of the modulating signal is not very high (less than 15 MHz), then such a signal can be digitized by a high-speed ADC synchronized with the laser module signal. However, since a narrowband signal is digitized (except for the modulation frequency, there are no other signals at the ADC input), it is possible to use the method of downsampling, due to which the sampling frequency of the ADC can be noticeably reduced to megahertz. The analog part of the laser system rangefinder is simplified.
It should be noted that both of the above laser techniques are often applied together – low-frequency signals are put directly to the ADC, high-frequency signals are transferred to the lower frequency part due to heterodyne conversion, and are also put to the ADC.

3D laser system scanning applications

The main application of this technology is laser system scanning. 3D laser system scanning is a relatively new direction in high-precision measurements. A background for its emergence and development was the appearance of reflectorless laser system rangefinders (tacheometers) that allow measurements to be made without the use of special reflectors, as well as GNSS technologies (Global Navigation Satellite System), which make it possible to quickly and accurately determine coordinates on the ground using satellite information.

Principles of operation of laser scanners

The principle of laser system device operation, regardless of their type and purpose, is based on measuring the distance from the source of the laser beam pulse to the object. The laser beam emerging from the emitter is reflected from the surface of the examined object. The reflected signal enters the scanner receiver, where the required distance is determined by the time delay (pulse method) or phase shift (phase method) between the emitted and reflected signal. Knowing the coordinates of the laser system scanner and the direction of the laser beam pulse, you can determine the three-dimensional coordinates of the point from which the pulse was reflected.
Modern laser system scanners provide the ability to generate measuring pulses with a frequency of up to several hundred thousand per second and, using a system of moving mirrors or the scanner body itself, distribute these pulses over the entire surface of the object. As a result of such measurements or “scanning”,  it is possible to get a cloud of three-dimensional points that describe the object under study with great accuracy and completeness in a short time.

Types of laser system scanners

Laser system scanners can be divided into 3 main types by their purpose:
– ground
– aerial
– mobile
Laser system scanners are also referred to as LIDARs (LIDAR – Light Detection And Ranging).

Ground scanning

A ground-based laser system scanner is installed at a point with pre-measured coordinates and scans surrounding objects. If it is necessary to obtain a more complete picture, scanning from several points/angles is performed, after which the clouds of reflections are “collected” into a single array.
The main applications of ground-based laser module scanning are indoor and outdoor surveying and modeling of architectural structures, industrial facilities (construction sites, workshops, electrical substations, mine workings, etc.). Also, such scanners are successfully used in such areas as the film industry and the creation of computer games.
The distance of ground-based scanners usually ranges from one to hundreds of meters. The resolution characterizing the density of reflections, as well as the accuracy of the reflection fixation are few millimeters.

Air scanning

Air laser system scanners can be installed on an airplane or a helicopter and are designed to capture large areas of terrain from the air during the flight. Since the position and orientation of the scanner are constantly changing, such laser systems are equipped with a GPS receiver and an inertial IMU system (Inertial Measurement Unit), which measures the position and orientation of the carrier/scanner in space in real-time. Base GPS stations are used to improve the accuracy of coordinate measurements, which provide information for calculating differential corrections that take into account the errors of satellite signals. Generally, digital photo equipment is installed on the carrier together with the scanning system, which allows carrying out aerial photography simultaneously with the laser system scanning.
The range of air scanners varies from several hundred to several thousand meters. The accuracy of recording reflections in height, 10-15 cm, in the plan, 1/2000 flight altitude, is due to the significant divergence of the laser beam. Thus, the planned accuracy will be no worse than 25 cm during terrain shooting from a height of 500m. 
The density of reflections is usually from one to hundreds of points per 1 square meter and depends on the frequency of the generated laser beam pulses and the flight altitude. The ability to capture several responses from each pulse allows receiving laser beam reflections from the surface of the earth hidden by vegetation – i.e., to restore the terrain where it is impossible to do so using traditional aerial photography.
Air scanning is used to capture both aerial and extended infrastructure objects, such as roads, pipelines, power lines, etc. The results of aerial laser system shooting are used in the design, inventory of objects, cartography, and many other laser applications.

Mobile scanning

Ideologically, the mobile laser system scanning is similar to air photography, only a ground platform is used here as a carrier – for example, a car, a railway train, or a boat. Usually, a mobile scanning system consists of 2 or more laser device scanners, several digital photo/video cameras, as well as GPS and IMU modules. The process of scanning is performed during the movement of the carrier along a road, railroad track, or water surface. 
Unlike an air scanner, the composition of objects that are in this zone of visibility is smaller, but the density of reflections, and hence the detail of point clouds, is significantly higher. For geography, the main difference from the air laser technique is that the GPS receiver of the mobile system, being close to the surface of the earth, often falls into the area of obscuring satellite signals from buildings, vegetation, and terrain features. Therefore, the problem of improving the accuracy of mobile scanning data is very relevant today.
The main application of mobile scanning is surveying roads and railways, bridges, overpasses, city streets, and coastlines.

Advantages and disadvantages of laser scanning

The main advantages of laser technology in scanning, of course, include the high speed of shooting, unattainable by any other measurement methods. Today, air laser scanning is almost the world standard in the field of power line surveys.
In this case, we should not forget about legal issues. For example, an appropriate permit related to both privacy issues and airspace use issues is required to obtain. This can take a very significant amount of time, which negatively affects responsiveness.
The main result of laser system scanning – whether it is ground, air, or mobile – is a cloud of three-dimensional points that describe the geometric parameters of the subject with varying accuracy. The number of laser beam reflections obtained during shooting the examined object is often hundreds of millions and even billions. Nowadays, the processing of such data arrays and the end product formation on their basis for users in various industries is the most time-consuming part of laser technology.
The use of laser scanning technology allows us to offer a variety of products that can be used to create geographic information systems, design, survey, and analyze the status of various objects, monitor engineering work, conduct a regression analysis, etc..
– topographic plans of different scales;
– orthophotomaps;
– digital terrain models;
– three-dimensional vector models of terrain and objects, including complex industrial structures;
– the results of various calculations related to the geometric characteristics of objects.

Applications in military and civilian industries

Laser system rangefinders are used both in the military industry:

• navigation target devices for armored vehicles, aviation;
• hand-held rangefinders for observers;
• fire control modules for hand weapons;
• air tracking systems.

Civilian applications

And in civilian life:

• Space geodesy
• Aerial geodesy
• Measurement of the sea depth
• Сonstruction activity
• 3D laser system scanning
• Machine scanning systems for robots

For example, recently, the staff of Forestry Tasmania introduced LIDAR data from a GIS to model and map forests that grow on Tasmania Island in southern Australia. During data processing by laser technology, including analysis of the general condition of the trees, the density of the canopy, and the volume of forest stands, they found the world’s highest deciduous tree.

Ultrathin fiber lasers

A compact fiber laser system that can operate inside living tissues without damaging them has been recently developed by a team of researchers from Northwestern and Columbia Universities. The developed fiber laser has a thickness of just 50 to 150 nanometers, which is considered to be about 1/1,000th the thickness of a single human hair. The advantage of the laser system’s size allows the laser to fit and operate inside living tissues, resulting in efficient detection of disease biomarkers or even potential treatment of deep-brain neurological disorders, such as epilepsy.

The researchers confirm that the tiny fiber laser system demonstrates specific promise for the imaging process in living tissues. Also, this laser system is regarded as a biocompatible one; it is possible to excite the fiber laser with longer wavelengths of light produced by a laser beam, enabling it to emit at shorter wavelengths.

Importance of wavelength selection

Longer light wavelengths are required for the bioimaging process because these laser systems are able to penetrate farther into tissues than visible wavelength photons. Laser beam light with shorter wavelengths is often needed at those same deep areas. Hence, the developed fiber laser system is an optically clean system that allows efficient delivery of visible laser beam light at penetration depths accessible to longer wavelengths.

Use in confined spaces and electronics

The tiny fiber laser can be used in extremely confined spaces, comprising quantum circuits and microprocessors for ultra-fast and low-power electronics. Although the need for increasingly tiny laser systems or laser modules does not decline, there is one disadvantage that the researchers face: tiny fiber lasers offer less effectiveness than their macroscopic counterparts, and these laser systems use shorter wavelengths to power them.

Challenges of tiny fiber laser operation

This disadvantage causes challenges because “the unconventional environments in which people want to apply tiny fiber laser systems are highly susceptible to damage from UV light and the excess heat generated by inefficient operation”. The researchers were able to develop a fiber laser platform that solves these problems by applying photon upconversion. “Low-energy photons are absorbed and converted into one photon with higher energy” in the fiber laser system during the process of upconversion.

Testing and results of the fiber laser

The developed fiber laser was tested, and the researchers succeeded in producing “bio-friendly” infrared photons and upconverted them to visible laser beams. The laser system can operate under low powers, and it is smaller than the light wavelength; it produces visible photons when optically pumped with light that human eyes cannot see. The compact fiber laser systems can function at powers that are orders of magnitude smaller than observed in any current lasers.

Successful testing of the fiber laser over the South China Sea

A team of Chinese researchers successfully tested a new fiber laser system mounted on a plane flying over the South China Sea earlier this year. The laser system enables reaching 160 meters below the sea surface, significantly boosting China’s naval deterrence capabilities.

The exact location and the environmental conditions can not be established by the fiber laser during tests. The required power applied to produce the laser beam must be large for a laser system to penetrate water efficiently.

Laser wavelength and penetration

According to the South China Morning Post, the fiber laser system emits green and blue light laser beams, which are regarded as being better equipped with the required wavelength to penetrate the surface of the water, where it is harder for light to achieve. The laser system power employed in previous tests was shut down due to the size limitations of laser modules; however, the latest test of the fiber laser may promote a crucial technological breakthrough.

Need for deep-reach laser systems

Modern submarines have a diving depth of 180 meters below sea level, although their real diving depth could be deeper. The laser systems with high reach are required. The fiber laser technology is considered to fundamentally change submarine warfare, resulting in an opportunity to detect another submarine before it enters the territorial waters of a country.

Comparison with Sonar technology

Sonar (sound navigation ranging) is the most popular submarine detection technique, but Sonar technology becomes inefficient when a water body gets busier. Then the laser system technology comes to help, whether there are airborne or even satellite-mounted fiber lasers.

Guanlan project and prospects

The research team takes part in the “Guanlan” (Sea Watcher) project, whose purpose is to develop a laser system satellite that emits a laser beam that can achieve 500 meters below the sea surface. Since most current submarines can be beyond the maximum depth thresholds and even much deeper, the test of the fiber laser system “simply formed another piece added to China’s “anti-access” military strategy, which is designed to deny anyone from entering its territorial waters”.

Detection capabilities and limitations

The detection systems based on fiber laser technology would enable Chinese military planners to be able to “triangulate and identify other vessels underwater”. Additionally, tests applying similar technology demonstrate the opportunity to penetrate 200 meters below the water’s surface; however, the laser systems still offer less efficiency in busy waters because it is possible to confuse them by sea life, clouds, or murky water.