Improving fiber lasers means that radiation weapons are about to appear

The ingenious configuration of industrial lasers will finally make laser weapons practical

The most advanced laser weapon in the US Morph fleet looks like an expensive telescope for beginners. It rises on the chassis of the amphibious assault vehicle USS Ponce and looks at the sky over the Persian Gulf, while its operator is sitting in a dark room somewhere on the ship, and is holding something like a game controller. In front of him on the screen you can see a small boat, located not far from Ponce, carrying some dark object. The infrared beam directed directly at this object is not visible, but one of the points suddenly becomes brighter, and then the object suddenly explodes, and metal fragments fly away from it, falling into the water.

This weapon, quickly assembled from several industrial lasers designed for cutting and welding, should produce only about 30 kW - and this is not the megawatt monster that military scientists have been dreaming of for decades to shoot down ICBMs . But this, as his supporters say, is a serious milestone on the path to a future in which weapons with directed energy will be deployed in real combat conditions. They add that this future will result from changes in mission and technology. Changes in the mission have been going on for years - from global protection from “unreliable states” possessing nuclear weapons to local protection against insurgents. Changes in technology are sharper, and lead to new solid - state fiber lasers . They form the basis of a $ 2 billion fast-growing industry in the United States, re-creating the available technologies for cutting and welding metals, and scaling them to even greater power, which has a devastating effect.


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Representatives of the Pentagon believe that high-energy laser technology, like the one tested on the already decommissioned Ponce, can play various roles both on land and at sea: destroy cheap missiles, artillery, drones, small boats loaded with weapons that the rebels introduce in operation in places like Iraq and Afghanistan. Today, the destruction of a rebel rocket costing several thousand dollars may require the use of a Patriot complex valued at $ 2-3 million. For comparison, a shot from a fiber laser can cost as little as $ 1 for diesel fuel, according to the military.

The military of other countries are also aiming at creating fiber lasers with a power level of about 100 kW, which is necessary for the reliable destruction of targets at a distance of several kilometers. The Chinese company Poly Technologies , the Israeli Rafael and the German defense company Rheinmetall have already developed lasers that are as powerful as the American prototype. Britain will spend £ 30 million to build a 50 kW Dragonfire laser, and Japan is exploring the possibility of using fiber lasers to block short-range and ballistic missile attacks from North Korea. The United States is leading the way, 15 years ago by launching a program to develop high-energy electrically-pumped lasers, and benefits from the rapid development of industrial fiber lasers, running IPG Photonics . The company, located in Oxford, Massachusetts, was founded in Russia in the 1990s, but then its headquarters moved to the United States in 1998. Its production facilities are located throughout the world and it dominates the international market for fiber lasers.

"The defense ministry wanted to get a laser weapon since the invention of the laser," said Robert Afzal, senior laser and sensor research officer at the branch of the defense company Lockheed Martin, located in Bozele, Washington. “The key element was the creation of a high-energy electric laser, small enough and powerful enough to be placed on trucks, airplanes and ships, and not remove all other equipment from there,” to make room for it. And although other technologies are currently being developed, it seems that fiber lasers are the first to be able to meet these requirements.

The Pentagon has been blinded by dreams of laser weapons since physicist Gordon Gould entered the Agency for the Study of Perspective Projects, which was then only a few months, in 1959, and suggested that they create a laser. Gould, one of the three people with whose names associated the creation of a laser, took advantage of the idea of ​​generating coherent light, expressed by a 37-year-old graduate student at Columbia University in late 1957. For several weeks, he sketched his version with a pair of mirrors located on opposite ends of a thin long cylinder. Smoking one cigarette after another over a pile of scientific works and his notebook, located on the kitchen table, he realized that the laser can concentrate light into a powerful beam. Having developed the idea of ​​a laser, Gould abandoned his research for a doctoral and patented the invention, eventually gaining the support of the company TRG, where he began work in early 1958.

In the first place in the list of tasks of the new division of the US Department of Defense was the task of protecting against nuclear weapons. Therefore, the new agency is very interested in the possibility of building a weapon operating at the speed of light. ARPA allocated $ 1 million (at current prices this is $ 8) to develop the Gould offer. Unfortunately, when the Pentagon decided to make this work secret, his involvement in the Communist Party at a young age prevented him from obtaining permission for access, which was necessary for working on his own project.

To create a powerful beam it took more than a pair of mirrors. It was necessary to place a certain source of light between the mirrors and think of a way to pump energy into this material. The first working laser was built on the basis of a solid synthetic ruby ​​containing chromium emitting light, which could be pumped with bright pulses of light from a lamp. Soon other types of systems appeared: it turned out that the discharge of current passing through a tube filled with helium and neon can generate coherent light. The same could produce pulses of current passing through the diodes of gallium arsenide, the edges of which were polished to a mirror shine.

But the Pentagon needed higher power, and from these sources it was impossible to achieve it. In the initially secret ARPA Siside project, researchers built solid-state lasers using rods a few centimeters thick, but most of the incoming light energy went to warm up the radiating solid, and little came out as a beam. Therefore, such an approach was abandoned. Similar problems forced to abandon the early gas and semiconductor lasers.

The military was ready to abandon laser weapons in the mid-1960s, when researchers from the Avco-Everett laboratory, located near Boston, invented an amazing new approach. They burned hydrocarbon fuels and forced the hot gas to pass through a series of rocket-like nozzles, so that the gas flowed between pairs of mirrors and generated tens of kilowatts of infrared laser light.


Fiber laser gun: the energy of diode lasers is pumped into a long segment of a special optical fiber with the addition of light emitting ytterbium atoms. The laser light travels along the length of the fiber, and is reflected from mirrors embedded in the fiber, and then comes out from one of the ends.


Inside fiber lasers: the laser consists of a three-layer fiber. The fiber shell has the lowest refractive index. Inside the shell is the outer core of the core with a slightly larger refractive index. This difference causes the light in its path along the fiber to be reflected from the outer core. Light crossing the inner core stimulates the emission of laser light by ytterbium atoms located in the inner core, which has an even higher refractive index.

Gas flow technology supported laser weapons research in the US Army during the Cold War. The development of new fuels capable of producing megawatts of energy led to dreams of creating military laser stations in orbit. US President Ronald Reagan has spent billions of dollars on the Strategic Defense Initiative , which explored the possibility of creating space lasers that shoot down Soviet ICBMs. At the end of the Cold War, the US Air Force spent billions more to shove a huge anti-missile laser into the Boeing 747, to use it to fight the launches from such “unreliable countries” as North Korea. In 2010, this megawatt monster really managed to knock down a ballistic missile during testing - this was his first success - but its use never approached the practical level. After that, Secretary of Defense Robert Gates cut down this program, declaring: “I don’t know a single person in uniform who would believe that this concept is a working one”.

The less powerful chemical lasers developed for the new anti-insurgent mission of the Pentagon, in the end, waited for the same fate. In 1996, the United States and Israel launched a joint program to test 100 kW chemical-powered gas lasers created by TRW (now part of Northrop Grumman). A high-energy tactical laser shot down missiles and artillery shells in 2000 and 2001. At about the same time, the terrorist attack on the USS Cole 2000 highlighted the danger of small boats and the need to seek protection from them.

But this laser from TRW showed two big problems. First, it was impractically large, and consisted of four trailers the size of a wagon each, and a separate beam guide, the size of a huge searchlight. Secondly, which was more important for Pentagon logistics experts, he needed special chemical fuels. This kind of fuel always causes logistical problems — any supply disruption can make a weapon useless. Worse, the chemicals themselves also represented weapons. Hydrogen fluoride, a gas capable of destroying the corneas, burning the lungs and seriously damaging the skin was generated in their reactions, which gave rise to enormous risks for the soldiers who served him.

In the meantime, another laser technology was developing rapidly. In the 1960s, Zhores Ivanovich Alferov from Russia [Soviet and Russian physicist, the only one of the Nobel Prize laureates in physics living in Russia, Vice President of the Russian Academy of Sciences from 1991 to 2017 / approx. transl.] and IEEE Medal of Honor winner Herbert Krömer from the United States invented structures that dramatically improved the performance of semiconductor devices, including diode lasers, by limiting the flow of light and electric current. This achievement in 2000 brought them the Nobel Prize in Physics. For 17 years, until 1977, Bell's laboratories extended the lifetime of diode lasers from seconds to 100 years, making it possible to use them in fiber-optic communications. After that, other laboratories dramatically increased power and efficiency, with the result that diode lasers could transform about half of the electrical energy they received into laser light.

Diode lasers did not generate the narrowly directed beams needed for weapons, but they opened up a new opportunity: to replace lamps as an energy source for solid-state lasers. These lasers, which emitted their light into sheets of glass or crystals containing light-emitting additives, had a great advantage over lamps, since they generated light more efficiently, which also consisted of waves of the same length. If you play with the composition of a semiconductor laser, you can choose the wavelength of light, which will be almost completely absorbed by the crystal, which will lead to an extremely effective conversion of its energy into laser. Pumping with diode lasers allowed the first models of an experienced laser weapon to convert about 20% of the incoming electricity to light - this was a huge improvement compared to 1% conversion in tube-pumped lasers.

High efficiency not only saves the Pentagon a couple of bucks on electricity bills. The incoming energy that has not been turned into light turns out to be parasitic heat, and limits the efficiency of the laser, since it must be removed. From a practical point of view, diode lasers made it possible to hope for the achievement of power in units and even tens of kilowatts, although they did not reach the megawatts needed for defense against long-range missiles.

Laboratory High Energy Laser Joint Technology Office (HEL-JTO) was launched to develop weapons based on solid-state lasers. Such systems, using sheets of glass or crystal, reached their peak in March 2009, when a demonstration from the Northrop Grumman Corporation took place. Their device produced a stable beam with a power of 105 kW for the whole 5 minutes. The laser did not require special fuel, it did not produce toxic gases, but it weighed 7 tons and occupied 10.8 cubic meters - which is comparable to the size of a truck-concrete mixer.

The military, of course, wanted something smaller in size than a concrete mixer. Another HEL-JTO program, the Robust Electric Laser Initiative, did the job. Having been instructed to develop a solid-state laser, better suited for use in combat, HEL-JTO set itself the task of building a 100 kW laser occupying 1.2 m ³ and capable of delivering more than 150 kW per kilogram, working with an efficiency no worse than 30%. Two of the four projects launched by the laboratory considered new versions of fashionable laser technology: fiber lasers.






Experimental fiber lasers are likely to be able to deliver the energy and efficiency needed to hit drones, small boats and other targets.

Fiber laser, in fact, is a fiber with important modifications. It has a central core, which has a slightly higher refractive index than the surrounding glass shell. Fiber for telecommunications uses a similar structure to transmit optical signals from laser transmitters over a central core consisting of extra-pure pure quartz, which does not generate any losses. But in a fiber laser, this central core contains light-emitting atoms, usually ytterbium.

Fiber lasers have another extra layer between the color-emitting core and the outer shell. This intermediate layer, the outer core or the inner shell, has a refractive index between the core and the outer shell. It consists of high-purity glass, and its task is to conduct light from external pump diode lasers directed into the outer sheath by means of separate fiber-optic cables. From there, light passes through the outer core, reflecting from the walls of its shell, constantly crossing the inner core, in which ytterbium atoms capture photons and emit laser light. The outer shell specifically has an irregular shape - D, ellipse, or even square - so that as much light as possible passes through the central core.

As a signal inside the fiber optic telecommunications cable, the light emitted by the ytterbium atoms remains inside the central core. But instead of passing tens of kilometers in one direction to the next optical amplifier or receiver, this light moves one way or the other, reflected from a pair of reflectors located at the two ends of the fiber. And with each pass, more and more ytterbium atoms emit light, increasing the power of the laser.

The tight fit of the inner and outer cores ensures that ytterbium atoms absorb most of the pumped light. In 2016, IPG Photonics reported that it had succeeded in converting more than 50% of its electricity into laser energy in the laboratory — much more than can be obtained with a solid crystal or glass, or with an older solid-state lasers scheme. Creating light in a long and thin fiber also allows you to get a very focused at large distances beam - and this is what is required for the transfer of lethal energy to a target that is several kilometers away. Since fiber lasers are thin — the fiber diameter is in the range of 125–400 microns — they have a very large ratio of surface area to volume, which allows them to dissipate heat much faster than shorter and thicker lasers do.

Fiber lasers started out small, they were a branch of the development of fiber amplifiers for long-distance telecommunications in the 1990s. Attempts to increase their energy began to do IPG. Starting with a 1W fiber laser in 1995, every three years the company added one order of power to this power up to 2012. The company itself also grew with the power of their lasers. In 2017, its sales reached $ 1.4 billion - about a third of the revenues of the entire market for industrial lasers.

Industrial fiber lasers are very powerful. IPG recently sold a 100 kW laser to the NADEX research laser center in Japan. He is able to weld metal parts with a thickness of up to 30 cm. But for the sake of such power, one has to sacrifice the ability to focus the beam at distances. Tools for cutting and welding need to work with objects located just a few centimeters from them. And the highest power that was achieved from a fiber laser with a beam suitable for focusing on objects located hundreds of meters away from them is 10 kW. But this will be enough for fixed targets like unexploded projectiles left on the battlefield, since the laser can be focused on explosives for quite a long time until it detonates.

Of course, 10 kW will not be able to stop the boat, carrying a bomb. The demonstration for the Navy at the USS Ponce used six industrial fiber lasers from IPG, each of which had a power of 5.5 kW, shooting through the same telescope to form a beam of 30 kW. But it will not be possible to get a beam with a power of 100 kW, capable of maintaining the focus needed to destroy fast-moving remote targets, simply adding light from additional industrial lasers and increasing the size of the telescope. For this, the Pentagon needed a single system capable of producing 100 kW. The laser had to track the movement of the target, focusing on a weak spot such as an engine or explosive, until the beam destroys it.

Unfortunately, this is not possible with the current approach. “If I could create a 100 kW laser based on a single fiber cable, that would be great, but I can't,” says Afzal of Lockheed. “It’s not possible to scale a single fiber to high energy.” Such power requires new technology, he adds.The leading candidate is the combination of the rays of a multitude of individual fiber lasers in some more controlled way than the simple direction of all the rays through a single telescope. And in this area two approaches look promising.

One idea is to precisely equalize the phases of light waves emanating from several fiber lasers so that they fold and form a single, more powerful beam. The light waves in each laser are coherent, that is, they move equally with each other - all the waves have peaks and troughs. In principle, the coherent combination of the rays of several different lasers should create a powerful beam that can be focused on targets located a few kilometers away. Phased array antennaThey can combine the coherent output of several radio transmitters, but this is much more difficult to do with light. The wavelength of light is orders of magnitude shorter - on the order of a micrometer, unlike centimeters in the case of radar - because of which it becomes extremely difficult to precisely combine the waves so that they constructively fold and not interfere.

Another approach involves ignoring the phases and combining the rays from many fiber lasers equipped with optics, which limit the light they emit in one short segment of the spectrum. As a result, each beam has its own, excellent wavelength. As a result, their combination produces a beam with a large scatter of wavelengths, and its components do not interfere with each other. This technique is called "spectral beam combination", and was adopted from the technologyspectral channel multiplexing , which has been extremely successful in cramming more data into existing fiber-optic communication channels.

For the introduction of this technology in Lockheed developed a special optics, deflecting the rays of individual fiber lasers at angles that depend on the wavelength - as the prism separates the colors of the spectrum. After that, the rays combine to form a single beam. In 2014, the company “created and tested for its money a 30 kW laser to deal with physics and engineering fundamentals,” Afzal says. The system combined 96 rays with different wavelengths of 300 W each into a single beam with a total power of 30 kW. At relatively low energies, lasers produce high-quality beams, which is why it is easier to combine them to produce a high-energy beam at the output than to build one high-energy laser with the same beam quality as Afzal asserts.

Last year, Lockheed was able to scale this technology to 60 kW, when it introduced a model for installation on a military truck, prepared to participate in battles. This laser "set a world record for the effectiveness of military solid-state lasers, exceeding 40% of the bar," says Adam Aberle, head of the development and demonstration of high-energy lasers technology. With such efficiency, a laser system with a 100 kW beam produces less than 150 kW of parasitic heat. Compare this with 400 kW of parasitic heat, which gave the laser, made on a different technology in 2009 by Northrop Grumman. March 1, Lockheed announced that by 2020, the US Navy will supply two copies of similar lasers called HELIOS, which will have to produce no less power. The Navy will install one of them on the destroyerand integrates it into the combat system of the ship, and the second will check on land at the White Sands shooting range in New Mexico.

“We regard the development of a high-energy fiber laser with a combination of rays as the last piece of the puzzle,” says Afzal. Perhaps, but the search for the perfect laser weapon is far from over. Now, when the technology of high-energy lasers already looks viable, the military will have to think about how to deploy lasers in combat conditions and against what to use. And for this you have to develop, create, test, improve the equipment necessary to transform a powerful laser into a mobile weapon: this includes trucks, ships and airplanes carrying the laser; sensors and computer systems that recognize and track targets; power management systems that supply electricity to the laser; cooling systems that prevent overheating;optics for focusing a powerful beam on moving targets for sufficient time to destroy or incapacitate them.

And the equipment itself is not yet ready for such tasks. Research and development teams will transfer their lasers to military workgroups involved in the provision of hardware, for example, US Naval Sea Systems Command, to integrate the new technology into military plans and develop procedures to support its work. Working groups will also have to conduct critical mortality tests using lasers on the example of potential targets and develop strategies and tactics for their use in combat.

Simply put, the ability to shoot down missiles at a test site is not enough for laser weapons to deserve their place in the combat arsenal. It took the military almost 60 years to bring lasers to a state that would make them potentially useful for combat. But at the Pentagon, many higher ranks grew up on "kinetic weapons" - cannons and rockets - and it would be very difficult to convince them in the onset of the Buck Rogers era . Without broad support, there will be no money to finance the difficult and expensive work of deploying a radically new type of weapon. As one wit said (on another occasion): "There will be no bucks, nor will there be Buck Rogers."