The Laser Directed Energy Weapons (DEWs) offer a transformational ‘game changer’ to counter asymmetric and disruptive threats, while facing increasingly sophisticated traditional challenges. Laser technology provides major advantages for military applications over kinetic weapons due to High precision and rapid on-target effect, precise and scalable effects, avoidance of collateral damage caused by fragmenting ammunition, Low logistics overhead and minimum costs per firing.
The US Navy estimates the “cost per shot” of a laser at less than a dollar: missiles used for ship defense cost $800 thousand up to $15 million dollars each. Compared with conventional antimissile weapons systems in deployment, the FEL would be the most efficient and the most cost-effective.
Many countries are developing laser based directed energy weapons for battlefield and counter terrorism operations. The UK Ministry of Defence has officially awarded a £30m contract to produce a prototype laser weapon. The aim is to see whether “directed energy” technology could benefit the armed forces, and is to culminate in a demonstration of the system in 2019. The contract was picked up by a consortium of European defence firms comprising the companies MBDA, Qinetiq, Leonardo-Finmeccanica GKN, Arke, BAE Systems and Marshall ADG.
Some countries like US, Russia and China have reached high degree of maturity in developing laser based directed energy weapons. “Laser weapons are no longer a technological problem, It’s one of integration at the service level,” according to Lockheed executives. “The technologies now exist,” said Paul Shattuck, company director for Directed Energy Systems. “They can be packaged into a size, weight, power and thermal which can be fit onto relevant tactical platforms, whether it’s a ship, whether it’s a ground vehicle or whether it’s an airborne platform. “That doesn’t mean that giant city-melting lasers are on their way. Right now, the weapons are limited to the 15-30 KW scale; going much further requires figuring out how to deal with atmospheric interference, an issue which becomes more complicated with weapons mounted on airborne systems.”
Lockheed is on track to deliver a 60 KW laser for the Army by the end of the year, known as the RELY program, said Robert Afzal, a senior fellow with Laser and Sensor Systems, “we’re underway. So we’re building hardware right now and we’re beginning the integration.” “Laser weapons provide a compliment to traditional kinetic weapons in the battlefield,” Lockheed Martin said. “In the future, they will offer reliable protection against threats such as swarms of drones or large numbers of rockets and mortars.”
Russian Deputy Defense Minister Yuri Borisov has also revealed that the Russian military has commissioned several types of laser weaponry. Borisov said that laser weapons are no longer a novelty for the Russian armed forces, with the military already in the process of commissioning and even adopting several types of laser-based weapons systems. China too is involved in the work on laser weapons. In 2014, it was reported that an experiment by the Chinese Academy of Engineering Physics resulted in the downing of a small drone hit from a distance of two kilometers.”
Challenges in Development of Laser Weapons
Laser weapons have to overcome many challenges such as cost, size, thermal management, stability, and power requirements for a laser weapon to become operational. Dirt, dust, wind, clouds, rain, and inclement weather can also hamper a laser’s range.
Subrata Ghoshroy of MIT’s Science, Technology and Global Security Working Group wrote in the Bulletin of Atomic Scientists: Any weapon that relies upon light traveling through the atmosphere runs into the problems of dust, humidity, and fog—features which absorb and scatter the laser energy. In addition, atmospheric distortions such as turbulence can deflect a beam of light. And at the same time that the photons in a laser’s beam must overcome all of these obstacles, they must also stay focused in a tight column and keep advancing forward without diminishing in power. Meanwhile, the user of the laser weapon must account for the movement of the target, the movement of the firing platform, and any decoys, dummies, or multiple war warheads that the enemy throws up.
The development of laser weapons requires many critical technologies, first is development of lasers capable of generating powers in kilowatts to megawatts range to be able to produce useful damage effects on the target. For instance to destroy anti-ship cruise missiles would require a beam of 500 kilowatts and demand megawatts of power.
Chemical lasers are the only systems that have produced megawatt-level outputs, however, they require special handling because of toxic chemicals hence fallen out of favor. Another reason is that they rely on what is essentially an external/independent power source, and thus lack the key strategic value of directed energy weapons: a virtually unlimited magazine.
Solid state lasers are electrically powered, and they are separated into three types: Fiber solid-state lasers like LaWS, slab solid-state lasers, and free electron lasers. While they avoid the complicated logistics associated with chemical lasers, SSLs are generally not very efficient.
Existing lasers generally dissipate two-thirds to three-quarters of the energy as heat, requiring still-bulky cooling equipment to avoid overheating damage. Air cooling can yield an unacceptable delay between shots.
In turbulent atmospheric conditions, like dust and humidity, the laser must propagate efficiently and stay accurately focused on the target. The system must compensate for the movement of the target, the motion of the platform and the distortion of the beam from weather or environmental conditions.
Laser Weapons require beam control/fire control (BC/FC) system that tracks a target, measures range to the target, compensate for atmospheric turbulence, select an aimpoint (vulnerable area) on the target, focuses and points the laser beam. A high precision target tracking system is needed and beam pointing system having extremely low jitter depending on the distances involved.
Laser beams begin to cause plasma breakdown in the atmosphere at energy densities of around one megajoule per cubic centimetre. This effect, called “blooming,” causes the laser to defocus and disperse energy into the surrounding air. The scintillation of atmosphere also causes severe distortion or beam focusing. This requires Adaptive or deformable mirror consisting of thousands of miniature actuators that continuously predistort the beam for it to remain focused.
Coherent and incoherent beam combining technologies are also used to increase the power levels. Battle management systems are also required to manage the weapon.
The high power requirements, large magazines and present low efficiency of lasers imply enormous power supply needed to operationalize laser weapons. Only large cruisers and destroyers have enough power under battle conditions to support lasers as well as additional power generating and cooling equipment.
Professor of Military Sciences Vadim Kozyulin points out, “the problem with laser weapons is that to function they require an enormous amount of energy. The main problem is to create a battery capable of feeding the laser cannon so that it can fire not one but several hundred shots.”
“A series of problems remain unresolved,” Svobodnaya Pressa, said columnist Anton Mardasov. “Firstly, is the problem of excess heat. In the American Boeing-based ‘flying laser’ project, upwards of 80% of pulse energy was lost in the form of heat, and even in testing on the ground the aircraft’s paint literally began to burn away from its intensity.” “Secondly, the issue of the beam being scattered has not been resolved; dust, soot and smoke scatter the laser beam, weakening it. Thirdly, scientists are yet to create an optical lens capable of withstanding powerful laser beams; following one serious pulse, the melted lens needs to be replaced. According to some experts, this, along with the price, is one of the main obstacles to the use of laser-based weapons in space – one shot and the optical lens fails, and the system itself becomes much too hot.”
New technologies breakthroughs enabling development of powerful Laser Weapons
Researchers are working on many enabling technologies of Laser Weapons like high power and efficient lasers, Coherent and incoherent beam combining technologies, high power and energy density sources and counteracting the effects of atmospheric turbulence.
Energy generation and storage technologies
The development of laser weapons requires many critical technologies, first is development of lasers capable of generating powers in kilowatts to megawatts range to be able to produce useful damage effects on the target. Laser require a power of the order of 100 kW, to be employed as directed energy weapons, in varieties of missions such as wide-area, ground-based defense against rockets, artillery and mortars; precision strike missions for airborne platforms; and shipboard defense against cruise missiles. To destroy anti-ship cruise missiles would require a beam of 500 kilowatts and demand megawatts of power.
One of the advantages of laser DEW is availability of Deep magazines. In contrast to SAM batteries which can carry finite numbers of interceptor missiles in their missile launch tubes, an electrically powered laser can be fired again and again, as long as the ship has fuel to generate electricity (and sufficient cooling capacity to remove waste heat from the laser). Electricity, the total number of shots they can fire is limited only by the amount of chemical fuel available or, in the case of solid-state lasers, the fuel available to drive the electrical power source.
Therefore both of the drivers of increased power requirements to enable wide range of military missions as well as enabling deep magazines increase the challenge of generating operational power requirements as well as thermal management becomes critical.
China develops most powerful super capacitor to power lasers
Now, a research team from Peking University and the Chinese Academy of Sciences led by professor Huang Fuqiang has reported a breakthrough in capacitor technology. In a paper published in the latest issue of the journalScience, they describe how the power density of their supercapacitor can reach 26 kilowatts per kilogram, or 130 times that of lithium-ion batteries.
A supercapacitor (SC) is a high-capacity electrochemical capacitor with capacitance values much higher than other capacitors (but lower voltage limits) that bridge the gap between electrolytic capacitors and rechargeable batteries. They typically store 10 to 100 times more energy per unit volume or mass than electrolytic capacitors, can accept and deliver charge much faster than batteries, and tolerate many more charge and discharge cycles than rechargeable batteries. They are however 10 times larger than conventional batteries for a given charge– some are bigger than shipping containers.
The Yal-1 laser cannon required a power output of one megawatt. A capacitor required to meet that power demand, using conventional technology, would weigh more than 10 tonnes. Huang’s team’s new supercapacitor, in theory, would weigh 40kg.
“A significant weight loss in the power unit can reduce the overall mass of a laser system. It can extend the application of laser weapon to fighter jets or even spacecraft,” said Professor Zhu Heyuan, an expert of laser technology at Fudan University in Shanghai, who was not involved in the research. “If the new technology really works and wins a nod from military, a Star Wars weapon may not be very far from us.”
A remaining problem for capacitors is their very low energy-storage capacity, which means their high power output might not last long enough to inflict fatal damage on an enemy target. Huang’s supercapacitor broke the traditional limits of ordinary capacitors with an ability to store 41 watt-hours of electricity per kilogram. Though lower than a lithium battery, it was equivalent to lead-acid cell batteries used in cars today. It was the first time that a capacitor could store as much energy as a mainstream battery.
High Power and efficient Fiber Lasers
The push to optimize the size, weight and power (called SWaP in military parlance) of field deployed laser weapons has driven a progression in the technology of the gain material used from chemical (e.g. deuterium fluoride), to solid state, and, most recently, to fiber.
Fiber lasers have emerged most promising technology, for directed energy weapons due to their many advantages like: high electrical to-optical efficiency (40%), high reliability for operation in harsh military environments, and high beam quality near diffraction-limited light output.
Laser require a power of the order of 100 kW, to be employed as directed energy weapons, in varieties of missions such as wide-area, ground-based defense against rockets, artillery and mortars; precision strike missions for airborne platforms; and shipboard defense against cruise missiles.
Both solid state (e.g. slab and rod) and fiber lasers can be diode pumped, and diode power supplies and pump modules themselves are electrically efficient and lend themselves to miniaturization. This efficiency, in turn, reduces the cooling requirements, and all its attendant equipment (pumps, heat exchangers, etc.).
Currently, individual fiber lasers can deliver up to about 2 kW of power, but multiple units can be combined to deliver around 10 kW in a single beam with extremely good mode quality.
for more information on fiber laser technologies: http://idstch.com/home5/international-defence-security-and-technology/technology/photonics/high-power-efficient-fiber-lasers-developed-deploy-laser-directed-energy-weapons-trucks-warships-airplanes/
General Atomics’s compact 150 kW High Energy Laser (HEL)
General Atomics revealed in April 2015 that its Gen 3 High Energy Laser (HEL) completed beam quality and power measurements tests. The Gen 3 laser has a number of upgrades that provide improved beam quality, increased electrical to optical efficiency, and reduced size and weight; the assembly is small at only 1.3 by 0.4 by 0.5 metres (4.3 × 1.3 × 1.6 ft), and is powered by a compact Lithium-ion battery to demonstrate deployability on tactical platforms. Beam quality remained constant through the 30-second demonstration, proving that the beam quality of electrically-pumped lasers can be maintained above 50 kilowatts.
General Atomics’s Tactical Laser Weapon Module includes high-power-density lithium-ion batteries, liquid cooling, one or more laser unit cells, and optics to clean up and stabilize the beam before it enters the beam-director telescope. A unit cell produces a 75 kw beam, and modules can be combined to create beams of 150-300 kw in power.
General Atomics is undertaking a privately funded study to integrate a 150-kilowatt solid-state laser onto its Avenger (née Predator-C) drone. GA-ASI has designed a power system for drone lasers that works almost like a hybrid car, the non-plugin kind. “You use the aircraft power to charge an intermediate storage system, and then that runs the laser when it’s doing laser shots,” said Michael Perry, Vice President for Mission Systems at GA-ASI.
Because an FEL’s photons—the concentrated particles of light composing the laser beam—have the potential to be powerful enough to destroy cruise (and ballistic) missiles many miles away, FELs are called the Holy Grail of military lasers.
In an FEL, the electrons are produced in an electron injector and injected into a particle accelerator, which kicks them up to fantastically high energy levels. Researchers at AOT recently built and successfully tested an advanced injector—a key FEL component—that produced a beam of electrons powerful enough for a megawatt-class (one million watts) antimissile FEL weapon.
The electrons are created by a photocathode inside an injector—a photoelectron injector—and are then injected into the particle accelerator. “The photoelectron injector was invented at Los Alamos,” explains Nguyen. “Electrons make a high-gain medium, which makes a powerful FEL possible. Using this technology, it becomes feasible to amplify 1 watt to 1 megawatt!” These waves of electrons, traveling at the speed of light inside the accelerator undulate between a series of alternating magnets, which causes the electrons to emit the powerful beams of photons.
“We accelerate the electrons through a series of radio frequency (RF) cavities, known as. RF accelerators, to almost the speed of light. The resultant energy of the electrons ranges from tens of millions to hundreds of millions of electronvolts,” says Dinh Nguyen, who co-leads the Laboratory’s FEL research team. These electrons are used to create the high-powered photons that make up the precise and concentrated beam of light of the FEL. “Our injector increased the electron beam current by a factor of 10 over what was previously demonstrated. A megawatt FEL is no longer theoretical.” This injector can operate continuously, meaning the FEL can fire continuously and destroy multiple targets
This is “a major leap forward for the [FEL] program,” says Quentin Saulter, the ONR’s FEL program manager. “You need megawatts of laser power to destroy a cruise missile,” says Nguyen. “The laser kills with heat. Extreme heat destroys the missile’s mechanics and electronic guidance systems, making it aerodynamically unstable so it tumbles wildly out of control. Extreme heat can also ignite the missile’s fuel, causing it to explode. But there’s not much time to heat up a missile. You need a tremendous amount of heat, like that from a megawatt laser, and a beam several feet in diameter to cook something like a missile that quickly.” He adds, “Imagine being able to use a ‘super blowtorch’ to destroy something that’s miles away…”
The FEL is an ideal countermeasure for ships because its beam can be optimized for varying atmospheric conditions at sea. For example, substances in the atmosphere— particularly water vapor, but also smoke, salt particles, dust, pollen, and other pollutants—absorb and scatter light. At sea, absorption by substantial amounts of water vapor is a particular problem for lasers. The problem of light absorption increases as the distance the light travels increases, reducing a laser’s effectiveness against distant targets.
Yet, there are wavelengths of light in the electromagnetic spectrum where light absorption by water vapor is markedly less, creating a window in the vapor for the light to pass through. These windows change along with atmospheric changes. FELs overcome these problems because they can be operated at different wavelengths. Indeed, FELs have the widest frequency range of any type of laser. This means FELs’ wavelengths are tunable—they can be changed, in essence, by the turn of a dial. If an FEL’s operators know the wavelengths that will become attenuated in the atmosphere, they can adjust the FEL’s wavelength to a different wavelength. By finding the window, the FEL’s beam of light travels longer distances.
China and Japan develop petawatt lasers
Researchers from Shanghai have created the most powerful laser beam ever made with potentially wide-ranging applications in fields from nuclear physics to high-tech weaponry, according to their paper published in the latest issue of the journal Optics Letters.
The beam reached a peak power of 5.13 petawatts (1 petawatt is equal to 1 billion millions watts), dwarfing the record set recently by Japanese scientists.
However It cannot sustain its peak power output for long, and lasted for less than 30 femtoseconds (30 quadrillionths of a second), according the to the team. Its poor power of endurance means that the total amount of energy generated by a single pulse was very low – 190 joules,
The new record was generated at the State Key laboratory of High Field Laser Physics under the Shanghai Institute of Optics and Fine Mechanics. The team was led by Professor Li Ruxin.
“Conventional laser weapons take very different designs. The original purpose [of the Shanghai beam] is not to form part of a laser gun or cannon,” said Li, a researcher at Chinese Academy of Sciences’ Key Laboratory of Functional Crystals and Laser Technology in Beijing. Li was not involved in the research. Nonetheless, future military applications cannot be ruled out, Li said.
Beam combining technologies
However, the power of state-of-the-art single-mode fiber lasers is limited by by thermal and nonlinear effects to 10 KW. Combining multiple low power lasers with good beam quality into one high-power beam helps in overcoming power limitations of fiber lasers. The large number of single mode fiber lasers can be combined either coherently, spectrally or incoherently. Coherent combination is the best technology, but requires extremely narrow laser line widths and precise control of the polarization and phase of the individual lasers.
Many prototype DEWs have been realized and tested utilizing beam combining technologies, Lockheed Martin In May 2013, shot down rockets with a portable 10kW fiber laser from about 1.5 km and demonstrated 30 kW in 2014, In October 2012, MBDA Systems’ German subsidiary used its 40kW system to shoot down airborne artillery from a distance of 2 km and The US Defense Advanced Research Projects Agency (DARPA), under its “Excalibur” project, claims that its developmental laser weapon has precisely hit a target from 7 kilometres.
Coherent arrays of fiber lasers appear scalable to weapons-class (100kW) powers with near-perfect beam quality in rugged and compact packages. Gregory Goodno, from Northrop Grumman Aerospace Systems, describe one coherent beam combining architecture, wherein a master oscillator is split to seed N fiber channels, followed by individual phase, polarization, and path length (P3) components , followed by a kilowatt-class fiber amplifier chain. To launch light into free space, kilowatt fiber tips were mounted into a close-packed, thermally stable array.
The use of coherent detection enables scaling of the P3 controller to hundreds of fiber-laser channels with high control bandwidths, allowing for the rejection of vibrational disturbances that may be coupled from the environment or platform of operation. They were able to achieve 80%, combining efficiency that could be increased to 90% or more, according to author.
MIT Lincoln Laboratory demonstrates optical phased array
Researchers from MIT Lincoln Laboratory’s Laser Technology and Applications Group were invited by DARPA to Wait, What? to demonstrate the advanced, 101-element optical phased array that they had developed under the agency’s sponsorship. At the Laboratory’s booth, the engineers conducted demonstrations to highlight the capability of this unique fiber laser that coherently combines an array of 101 optical emitters to produce a powerfully bright single beam. A high-brightness, concentrated beam can enhance various applications including directed energy weapons.
The researchers explained to visitors that the challenge in developing this laser is to have the individual beams from all 101 emitters arrive at precisely the same time to a designated point in the far-field plane. To achieve this simultaneous arrival, all the path lengths of the 101 emitters need to be matched to much less than a 1 μm wavelength (less than 1/50th the diameter of a hair). The research team solved the synchronization of the beams by maneuvering a set of phase modulators, which sped up or slowed down the beams such that they all arrived together to create a bright central spot at a target.
The team also demonstrated phase-control algorithm that enabled the phased-array beam to track the moving target. After they showed visitors how to steer a beam and how to compensate for the random fiber path-length variations in an environment that does not have turbulence and atmospheric disturbances, the Lincoln Laboratory team demonstrated beam propagation in a more challenging environment.
They injected hot air into a segment of a beam path so viewers could watch on a monitor how the beam degraded because of the disturbance to it caused by the air’s motion. “Our control algorithm compensated for the disturbance by iteratively applying a correction to all 101 emitters in order to optimize the central intensity of the beam,” said Montoya, who further explained that the algorithm predistorts the 101-element beam before it propagates through an atmospheric disturbance.
Lockheed Martin’s Adaptive Aero-optic Beam Control (ABC) turret
Northrop Grumman has been awarded a USD39.3 million contract related to the development of a laser-based self-defence system for the US Air Force (USAF). Northrop Grumman will develop and deliver an advanced beam control system for integration as part of a complete laser weapons system into a tactical pod for USAF fighter aircraft. Work is expected to be complete by 31 August 2021.
It is intended that the SHiELD pod would better enable the USAF’s fourth-generation fighter fleet, such as the Boeing F-15 Eagle and Lockheed Martin F-16 Fighting Falcon, to survive in contested airspace. The fifth-generation Lockheed Martin F-22 Raptor and F-35 Lightning II would probably not carry the pod, as it would negate their stealth characteristics.
Lockheed Martin in partnership with the Air Force Research Laboratory (AFRL) and the University of Notre Dame, has demonstrated the airworthiness of a new beam control turret to give 360-degree coverage for high-energy laser weapons operating on military aircraft. A research aircraft equipped with the Aero-adaptive Aero-optic Beam Control (ABC) turret conducted eight flights in Michigan.
“These initial flight tests validate the performance of our ABC turret design, which is an enabler for integrating high energy lasers on military aircraft,” said Doug Graham, vice president of advanced programs, Strategic and Missile Defense Systems, Lockheed Martin Space Systems.
The ABC turret system is designed to allow high-energy lasers to engage enemy aircraft and missiles above, below and behind the aircraft. Lockheed Martin’s flow control and optical compensation technologies counteract the effects of turbulence caused by the protrusion of a turret from an aircraft’s fuselage.
Deformable mirrors ‘tame’ turbulence for laser weapon
US defense contractor Lockheed Martin says that its optical technology, based around a deformable mirror system similar in principle to that used by large ground-based telescopes to sharpen up astronomical images distorted by the Earth’s atmosphere, can overcome a key technological problem – turbulence. The company has been testing the system, albeit with a low-power green laser on board a business jet, for more than a year.
Counteracting the effects of atmospheric turbulence becomes particularly important when dealing with the long stand-off distances at which airborne laser weapons need to engage with targets – likely to be tens of kilometers, given the speeds involved. Those distances mean that scattering of the laser light by atmospheric turbulence becomes more problematic.
“The aero-adaptive aero-optic beam control (ABC) turret is the first turret ever to demonstrate a 360-degree field of regard for laser weapon systems on an aircraft flying near the speed of sound,” announced Lockheed. “Its performance has been verified in nearly 60 flight tests conducted in 2014 and 2015 using a business jet as a low-cost flying test bed.
”Because enemy aircraft and missiles can come from anywhere, and at very high speeds, an airborne system must be able to track incoming threats with an ultra-rapid response time and then fire in any direction. The company added in a press release: “As the aircraft traveled at jet cruise speeds, a low-power laser beam was fired through the turret’s optical window to measure and verify successful performance in all directions.”
The company also announced earlier that it was about to begin production of high-power fiber laser modules for military applications, with the US Army pencilled in to receive a 60 kW system suitable for mounting onto a truck.
Global Directed Energy Weapon (DEW) Market to be worth $5,343MN in 2017, according to “Directed Energy Weapons (DEW) Market Report 2017-2027.”
The report also provides profiles of 13 leading companies operating within the market including Azimuth Corporation, BAE Systems plc, Battelle, The Boeing Company, General Atomics, General Dynamics Corporation, Kratos Defense & Security Solutions, Lockheed Martin Corporation, MBDA, Northrop Grumman Corporation, Rafael Advanced Defense Systems Ltd, Raytheon Company and Rheinmetall AG.
References and Resources also include: