Category: Fiber Laser Technology

Principle of operation: LED vs semiconductor lasers

The operation principle of an LED and a traditional semiconductor laser system is practically the same, which means that light is emitted during the combination of electrons and holes. The main difference is that the light of LEDs is emitted in a narrow spectral range, while the light from semiconductor lasers is emitted in a single wavelength.

Emission wavelength and applications

The emission wavelength of devices depends on the materials used. Thus, semiconductor laser systems emit the wavelengths whose ranges vary from infrared to ultraviolet. The laser applications include such fields as fiber optic communication, barcode readers, disc readers, and laser printing, but the use of laser systems as an illumination product remained impractical up to now.

Resonant cavity in semiconductor lasers

Similar to conventional laser systems, semiconductor lasers have a resonant cavity to facilitate amplification; the cavity consists of two parallel planes, separated by a few hundred µm, that operate as mirrors to direct emitted photons back into the resonant cavity.

Comparison with LEDs

There are some similarities between traditional LEDs and semiconductor laser systems, for example, their source of power is a driver converting AC to DC; they both suffer from a drop in light output at increasing temperatures. Semiconductor lasers are not receptive to a “droop” process, during which the increase in drive current causes lower efficacy.

Advantages of laser-based headlamps

In spite of the fact that usual blue LEDs offer higher efficacy than semiconductor laser systems provide, this is so only at lower input currents. This is the reason why BMW company offers headlamps based on a laser system that makes them 10 times brighter than traditional LED headlamps and 30 percent more efficient.

Working principle of laser headlamps

The principle of the laser headlamps’ operation is based on the creation of white laser beams by reflecting semiconductor laser light around inside the headlamp body frame using accurately established mirrors, then focusing the laser beam through a phosphor-filled lens, producing a white light of high intensity.

Efficiency and future potential

Semiconductor laser systems can provide efficiencies of a hundred times or even more than that of traditional LEDs, allowing higher light output from the laser beam with smaller die sizes. The laser system still requires some improvements for future laser applications because of the extremely narrow emission cone (about 1-2 degrees).

Semiconductor laser systems will be applied in architectural illumination products for which a narrow, high-quality laser beam is advantageous. It is possible to place lighting for museums, galleries, retail spaces, and other settings in a small area instead of being spread throughout.

Role of micromachining in modern manufacturing

The process of fine details micromachining plays a very important role in high-volume manufacturing in various fields of laser application, such as consumer electronics, medical devices, and the automotive industry. Highly accurate laser systems allow for the production of tiny holes, fine cuts, and narrow scribes. For example, the production of a usual smartphone that has thousands of details requires making millions of drilled holes and accurately cutting parts with fiber lasers.

Accuracy and quality, high throughput, and a low cost per unit are required for micromachining these fine details. Although mechanical methods, for example, drilling, milling, sawing, and sandblasting, can be suitable in quality and offer minimal heat damage, there are some limits on the size and consistency of details.

Compared to mechanical and other methods, laser technology provides higher accuracy, smaller details, and improved consistency with no laser system wear. The achievement of the mentioned characteristics required great advances in laser technology that were achieved just in recent years.

Purposes of micromachining with fiber lasers

One of the purposes of micromachining by the laser system is considered to be the removal of only the required material, generally through the method of localized heating. At the same time, the fiber laser minimizes heating and damage. To achieve the required result, it is necessary to deliver high-quality irradiation from a near-perfect laser beam accurately to the target region.

High throughput

Shorter wavelengths and shorter pulse widths are important in achieving the results. Moreover, the second purpose of the micromachining process made by the laser system is the opportunity to reach high machining throughput. It should be noted that the increase of average output power in the fiber laser results in higher ablation rates, however, with certain limitations.

Solutions through pulse tailoring

A possible solution to the current problem is tailoring the pulse sequence produced by a laser beam, with pulse bursts and pulse shapes. The energy-time profile from the laser beam is able to be tailored and optimized for a certain material and its interaction with the fiber laser system light so that the incident energy can be employed almost entirely for material removal and not excess heating.

Cost considerations in micromachining

The laser system cost is considered to be a key factor for the micromachining industry. The cost increase from the fiber laser process for each manufactured detail is the most crucial figure that contains such parameters as amortization of the upfront laser system cost, cost of operation, lost productivity from downtime, and process yield.

New ceramic welding technology

A totally new laser technology for the ceramic welding process was presented by engineers from the USA. The laser technology is based on the use of a pulsed fiber laser that emits a series of short, ultrafast laser beam pulses to melt ceramic materials, along with the interaction between two ceramic parts, and fuse them. Additionally, the melting is local because the process of heating focuses only on the interface, resulting in the technique of “ultrafast pulsed fiber laser welding”.

Optimization of laser parameters

To make this laser system technology work, the optimization of the transparency of the ceramic material, as well as fiber laser parameters such as exposure time, number of laser beam pulses, and duration of pulse, is required. The combination of these aspects allows achieving optimal results, the laser system energy couples strictly to the ceramic, making the use of low laser beam power (less than 50 watts) possible at room temperature.

The “sweet spot” for ultrafast welding

“The “sweet spot” for the ultrafast laser beam pulses was two picoseconds, at the high repetition rate of one megahertz, along with a moderate total number of pulses”. The developed pulsed fiber laser technology enables increasing the melt diameter, reducing material ablation, and synchronizing cooling just right for the best weld process possible.

Temperature control and precision

The engineers have succeeded in escaping temperature gradients from being set up throughout the ceramic due to the accurate focusing of the energy from the laser beam. Finally, the current fiber laser technology allows encasing temperature-sensitive materials without damaging them.

Demonstration and applications

The technology of pulsed fiber laser was already tested and demonstrated: the engineers welded a transparent cylindrical cap to the inside of a ceramic tube. The welds made by the pulsed laser system are strong enough to hold a vacuum environment. There is a similarity between the vacuum tests of welds made by the pulsed fiber laser and the tests used in industry to control seals on electronic and optoelectronic devices.

Challenges of traditional methods

The engineers confirm that it was impossible to encase or seal electronic components inside ceramics before the development of laser technology because it was necessary to install the entire assembly in a furnace, which would damage the electronics.

Prospects of pulsed fiber laser welding

The main application of the ultrafast pulsed fiber laser in the welding industry was the welding process of tiny ceramic features (less than 2 cm in size). Nowadays, it is planned to optimize the fiber laser technique for larger scales, as well as for various types of materials and geometries. 
Due to laser system technology, the welding process could make ceramics an integral part in devices for harsh environmental conditions, as well as in optoelectronic or electronic packages that require visible-radio frequency transparency.

The role of laser technology in eye surgery

Laser technology enables procedures to be continued in minutes, with the laser system process counted in seconds. Currently, laser technology enables eye surgery to enhance vision in just a few minutes. The main challenges are the cost of the procedure and the patient’s courage to undergo the laser treatment.

According to the World Health Organization, about 1.3 billion people have some form of vision disturbance; uncorrected refractive error is considered to be one of the most common causes. Possible solutions are eyeglasses and contact lenses, which are not always effective. Laser system eye therapy is an excellent option.

How laser surgery works

Laser surgery for the eyes provides a more lasting remedy for vision issues. The laser system-assisted in situ keratomileusis is regarded as one of the most common surgical procedures in eye treatment. This laser technology was first introduced at the beginning of the 1980s, and over 40 million procedures by laser beams have been performed globally since 1991. The principle of laser system operation is based on the creation of a flap in the corneal tissue, after which a laser beam reshapes the cornea through ablation.

Modern advances in laser surgery

Although the fundamental principle of laser technology has not changed, contemporary advanced technologies enable the use of a femtosecond fiber laser rather than a surgical blade to create the flap in newer methods. “The flap creation takes about 20 seconds, while the process of laser beam ablation is 15 to 20 seconds. The entire procedure itself takes 5 to 10 minutes per eye, with two eyes taking 15 to 20 minutes”.

Results and limitations of the procedure

Compared to traditional techniques, the application of a laser system makes the ablation process faster. Laser beam surgery is not a perfect procedure; that is why there is a range of accessible results, usually varying at around minus or plus 0.25 or 0.5. It is impossible to provide a perfect zero, but it is not the main purpose. The main purpose is to escape the need for glasses due to laser technology and to become as close to zero as possible.

Eligibility for laser eye surgery

Laser beam eye surgery from laser systems is available only for patients over 18 with healthy eyes (no infections or conditions affecting the eye aside from the refractive disorder) and excludes pregnant or currently breastfeeding women.

Development of a compact tunable fiber laser

A team of researchers from the U.S. developed a compact laser system that enables a tunable fiber laser over a wide range. The fiber laser is made from commercial-off-the-shelf components and is designed to emit terahertz radiation by spinning the energy levels of molecules in nitrous oxide (laughing gas).

The tunable fiber lasers provide new data information from the novel computational techniques. This gas laser technology was regarded as old for a long time; therefore, researchers thought that the laser systems were big, low-power, and non-tunable, which is why terahertz sources are considered to be potential.

Compact size and efficiency

Modern tunable fiber lasers have a compact size, can be tuned, and offer more efficiency parameters. Additionally, it is possible to put this fiber laser system in one’s backpack or vehicle for wireless communications or high-resolution imaging. The design of the tunable fiber laser is based on the research done in the 1980s, according to which a gas laser system allows emitting terahertz laser beam waves; the fiber laser is smaller than conventional laser devices, and at a pressure far higher than the theoretical models of the time suggested.

Vibrational states and laser performance

Manufacturers of those fiber laser models did not pay attention to several vibrational states, “assuming that only a handful of vibrations were what ultimately mattered in producing a terahertz wave”. According to the previous models, if a cavity is tiny, molecules vibrating in response to an incoming infrared laser system will collide more often and produce their energy rather than building it up further to spin and emit terahertz waves.

Tracking molecular states

The new fiber laser model enables us to track thousands of relevant vibrational and rotational states among millions of groups of molecules within a single cavity. Then the laser technology performs an analysis of how those molecules respond to the incoming infrared laser beam, depending on their position and direction within the cavity. The researchers succeeded in discovering that the inclusion of all these other vibrational states in tunable fiber lasers (previously ignored by people) leads to the appearance of a buffer.

Quantum cascade laser as the infrared source

For the new model, a quantum cascade laser system has been chosen as the infrared laser beam source. The opportunity to change the frequency of the input fiber laser by turning a dial may change the frequency of the terahertz coming out. Several gas libraries were looked through by researchers in order to detect those that were known to rotate in a specific way in response to an infrared laser beam, finally deciding on nitrous oxide.

Prospects and gas molecules

The stimulation of the quantum cascade laser system results in the creation of a tunable fiber laser at a much smaller size than previously considered possible. Researchers include other gas molecules, for example, carbon monoxide and ammonia, offering a menu of various terahertz generation options with different frequencies and tuning ranges, paired with a quantum cascade laser system.

A combination of fiber lasers and direct-diode lasers

Fiber lasers are often used in combination with direct-diode laser systems. A fiber laser contains an optical fiber that is an end- or side-pumped, while a direct-diode laser system includes a non-gain optical fiber that is simply filled with light that is produced from numerous laser beam diodes connected to the fiber.

It is possible to apply both fiber lasers and direct diode laser systems for material processing. High-power fiber laser systems include either single-mode or multimode outputs, while direct-diode lasers are always multimode because “the etendue of fiber optics for combining light from many laser beam diodes will be substantially above the single-mode limit”.

Improving brightness and laser output

Manufacturers of laser systems are constantly improving the brightness of laser products; herein, numerous material processing applications require the multimodal laser beam. Additionally, the majority, but not all, direct-diode laser systems emit laser beams in the near-infrared.

High-power output through wavelength multiplexing

The wavelength-multiplexing of the laser stacks and polarization-combining submodules allows achieving high-power laser beams. Thus, it is possible to achieve a power of 6 mm-mrad over a broad range of power levels from 100 W to beyond 1000 W.

Transmission and wavelength range

Moreover, a laser beam can then be transmitted to the workpiece in free space or through optical fibers with a core size of 100 or 200 µm. Finally, the laser technology of wavelength multiplexing enables such laser systems to produce within a wavelength range of 900 to 980 nm.

Laser modules for cutting, welding, and pumping

Material processing application also uses laser modules for the same purposes. To be more precise, basic laser modules can reach a bandwidth of less than 25 nm and an output power of 1.5 kW. The application of laser modules includes cutting and welding, as well as high-energy laser pumping.

Advantages of wavelength-multiplexed laser modules

Nevertheless, the laser technology of wavelength multiplexing increases the power levels of this platform far into the multi-kilowatt range without any variation in laser beam properties. Laser modules can include high-power fiber optic cables and laser processing heads, resulting in higher power and efficiency.

Applications in microelectronics, soldering, and heat treatment

The laser system demonstrates the ideal application in soldering microelectronic parts, where relatively tiny spot sizes varying from 0.2 to 3 mm are set over a fairly long working distance. Also, the fiber laser system offers such benefits as quite short rise- and fall-times (less than 10 µs), it keeps up a uniform power distribution across the laser beam, resulting in a perfect solution for multiple heat treatment applications.

Current challenges in conventional laser systems

Lasers are universal tools that nowadays find numerous applications, from entertaining our cats to encryption and coding communications. Conventional laser systems can be energy-intensive; the majority of them are made employing toxic materials, for instance, arsenic and gallium. Thus, it is necessary to find new materials and technologies to make fiber lasers more sustainable.

Discovery of a new high-efficiency fiber laser

A group of researchers from the U.S. has discovered a new phenomenon that leads to the creation of a fiber laser system with over 40% efficiency, which is nearly ten times higher than other similar laser systems. The new laser is made from a glass ring on a silicon wafer with only a monolayer coating of siloxane molecules anchored to the surface.

Advantages of the new laser system

Compared to previous versions, this laser system offers improved power consumption, and it is made from more sustainable materials. The operating principle of the surface laser system is based on an extension of the Raman effect that allows understanding how the interaction of light with a material can lead to molecular vibrations resulting in laser beam light emission.

Moreover, this type of laser system has one unique characteristic: the emitted wavelength is determined by the material’s vibrational frequency, but not by its electronic transitions. It is easy to adjust the emitted laser beam light by changing the incident light.

Applications of Raman-based fiber lasers

The laser systems based on Raman technology have numerous applications, such as military communications, microscopy and imaging, the medical area for ablation therapy, a minimally invasive procedure to destroy abnormal tissue such as tumors. The main purpose is to produce a fiber laser system where all of the incident laser beam light will be changed into emitted light.

Challenges in solid-state Raman lasers

In a usual solid-state Raman laser system, the molecules interact with each other, resulting in a performance reduction. That is why a new approach is required to be developed to overcome this challenge. The researchers confirm that if traditional laser systems are regarded as the old energy-inefficient light bulbs, new laser technology will make new laser systems as energy-efficient as LED light bulbs – a brighter result requiring lower energy input.

Improved efficiency via molecular surface constraint

Finally, the efficiency of motion movement is increasing, as well as the ability to act as a laser system by constraining the motion. The molecules are set on the surface of an integrated photonic glass ring that limits an initial laser beam light source. The laser beam light inside the ring excites the surface-constrained molecules, providing an efficiency of nearly 10 times higher, despite there being less material.

New fiber laser technology for nonlinear effects

A novel fiber laser technique for generating second-order nonlinear effects in materials that typically cannot accommodate them could lead to new possibilities for creating these effects for optical computing, fast data processors, and bioimaging. A team of researchers from Georgia demonstrates a technique, based on a red fiber laser, to produce the nonlinear effects.

Laser system setup and experimental design

For the laser system, they develop an array of small plasmonic gold triangles on the surface of a centrosymmetric titanium dioxide or TiO2 slab in the laboratory. Then the gold structure is illuminated with a pulse of laser beam light. The laser beam operates like an optical switch; it breaks the crystal symmetry of the material.

Electron excitation and frequency doubling.

The laser beam pulse causes the electron excitation when it is fired at the array of gold triangles on the TiO2 slab; the excitation doubles the frequency of the laser beam from a second laser system as it reflects from the amorphous TiO2 slab. The fiber laser system has already been tested and demonstrated the blue laser beam that “shows the frequency-doubled light and the green beam that controls the hot-electron migration”.

Operating principle of the fiber laser system

The operating principle of the laser system is based on the optical switch that causes the excitation of high-energy electrons inside the gold triangles; therefore, some electrons go to the titanium dioxide from the triangles’ tips. “Since the migration of electrons to the TiO2 slab primarily happens at the tips of [the] triangles, the electron migration is spatially an asymmetric process, fleetingly breaking the titanium dioxide crystal symmetry optically.”

Symmetry-breaking and material applications

The red laser beam pulse leads to an instant induced symmetry-breaking effect. It is possible to break optically the crystalline symmetry of conventionally linear materials, for example, amorphous titanium dioxide; the fiber laser system allows making a range of optical materials wider. These materials can then be employed in numerous micro- and nanotechnology applications such as high-speed optical data processors.

Control and stability of nonlinear effects

A stable, continuous-wave laser system enables to production of the nonlinear effect to last for as long as the fiber laser is turned on. It is possible to control the number of migrated electrons through the intensity of the red laser beam. More electrons appear inside the gold triangles when the intensity of the optical switch rises, and more electrons are put into the TiO2 slab.

The fiber laser system still requires future improvements, but now it already offers numerous opportunities in the field of nonlinear nanophotonics, as well as plays a crucial role in the field of quantum electron tunneling.