Military Laser Technology for Defense: Technology for Revolutionizing 21st Century Warfare

Military Laser Technology for Defense: Technology for Revolutionizing 21st Century Warfare

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Further, MilitaryLaser Technology for Defense addresses how laser technology caneffectively mitigate six of the most pressing military threats ofthe 21st century: The author believes that laser technology willrevolutionize warfare in the 21st century. Military Laser Technology for Defense, includes Military Laser Technology for Defense: Technology for Revolutionizing 21st Century Warfare. Recent advances in ultra-high-power lasers, including thefree-electron laser, and impressive airborne demonstrations oflaser weapons systems, such as the airborne laser, have shown theenormous potential of laser technology to revolutionize21st century warfare.

Optical lnterferometers and Oscillators. Principles for Bound Electron State Lasers. Pulsed High Peak Power Lasers. Laser Protection from Missiles. Shown is the Pentagon viewed from more than miles in space. Newer versions team up with their IR cousins to furnish strategic and on-line tactical battlefield support data. These technologies include materials and systems for IR FPAs, charge-coupled devices CCDs , lightweight optics, compact coolers, staring arrays, and efficient electronic readouts and processors. These technologies are operated on-board satellites, uninhabited airborne vehicles UAVs , and aircraft.

UAVs can relay real-time images of battlefield troop deployments to field commanders as will future satellite systems. During World War II, the use of radar by Allied forces to see through clouds and inclement weather was invaluable. This capability was literally the difference between losing and winning battles. Now, some 50 years later, optical devices are available that can see at night with such important advantages over radar as high spatial resolution as good as ordinary eyesight and lack of detectable radiation emanation.

Early night vision units amplified reflected starlight and demonstrated considerable tactical advantages. Battlefield night vision devices now use passive detection of IR, which senses the heat radiated from objects in the scene. The challenge is to discriminate objects such as tanks, which may be only a few degrees hotter than the background.

Older devices produced images that resembled bad, noisy television signals; today, the devices have been improved to the level of quality television pictures. These devices, produced in large volume, have little in common with one-of-a-kind complex surveillance systems, although the underlying physical principles are the same.

It should be noted that this is not all-weather capability since heat radiation is absorbed by rain and fog, imposing well-understood operational military limitations. Night vision units, often termed FLIRs a historical acronym meaning forward-looking infrareds use FPAs in a wide variety of formats for tactical battlefield applications Lerner, Night vision designs are mass produced in quantities of more than 10, at low cost; for example, more than , first-generation units, known as Common Modules, have been built.

This is in contrast to the surveillance units discussed in the previous section, which have ultrahigh performance but are produced in limited numbers 1 to at high cost. The first night vision devices used cooled detectors to gain the sensitivity required to detect weak thermal radiation. The availability of detector materials has largely driven system design. Most modern FLIRs use mercury cadmium telluride HgCdTe, or MCT because the composition can be varied to afford detection over different regions of the IR spectrum and the elements can be mass produced with high purity. Cooling to the vicinity of K requires a mechanical device and dewar thermos bottle with a window and optical elements to admit thermal radiation.

Either the scene is scanned over a linear array of detectors with about 10 5 elements or a large array of detectors with about 10 5 elements stares at the scene to be imaged. Cooled detectors feature excitation of electrons as photons are absorbed photodetectors , with signal processing in chips followed by conventional display of the image. Basic materials research drives the progression as poor-quality bulk material gave way to liquid-phase epitaxy LPE material amenable to mass production at low cost. The older rotary coolers and bulk elements that made up the Common Module class of devices for the first-generation FLIRs used in Army vehicles were characterized by "noisy TV picture" quality and poor reliability.

This discussion cannot cover every type of night vision system insertion; a brief synopsis of the types of fielded units is provided here. Early uses focused on tank target detection and missile guidance. As the technology progressed and the sensitivity increased, aircraft and helicopters began to rely on FLIRs for targeting and navigation. The progression to lower-sensitivity, lower-cost units has permitted vehicle driving at night and use by individual soldiers. The most compact imaging IR devices are found in missile guidance units for Javelin and Stinger, for example.

Obviously, for expendable munition guidance applications, very low cost is paramount, but the performance is usually limited to short-range targeting. The most recent FLIR product breakthrough is in the area of uncooled detectors. Unlike the cooled photodetector class, uncooled detectors rely on the use of a silicon microstructure upon which a thin film of material is deposited. The temperature increase brought about by the absorption of IR changes some property of this film. The three detection methods used are 1 resistive bolometric, 2 pyroelectric, and 3 thermoelectric. The low cost of silicon microstructure devices is key to the widespread use anticipated for this detector class.

Consistent with this class, a sensitivity sufficient to image up to about 1 km is possible; material advances will improve this range. Courtesy of Raytheon Systems Company.

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With excellent pixel-to-pixel uniformity yielding imagery at an affordable cost, this type of unit is suitable for deployment to individual soldiers and is also expected to see widespread commercial use. Essential to the success of this technological thrust have been the cooperative efforts of the military services and DARPA to take the "black magic" out of detector producibility and to create a quality manufacturing infrastructure.

Future DOD thrusts are to develop even larger staring arrays, multicolor FPAs for fusion of detector information, wide deployment of more sensitive uncooled imagers, and development of effective automatic target recognition systems. Lasers have become such a key part of our life, at the grocery checkout counter and in compact disk CD players, that military uses are easily anticipated. Laser light projects long distances in very narrow beams because of its short wavelength, unlike radio waves that spread out. So optical power is more efficiently delivered to a target, and this simple idea is the essence of most military uses of lasers.

Early laser research workers dreamed of destroying targets at the speed of light a million times the speed of sound and a host of other applications. Even after lasers were improved, it was quite a chore to make laboratory units work reliably in the field. This section includes the analogues of microwave systems that operate in the atmosphere and space, namely, laser radar, jammers, target designators, communications, and laser weapons.

Solar cells, environment sensing, law enforcement, transportation, and so forth, also operating in the atmosphere or in space for civilian use, are treated in Chapter 3. In military applications we are usually concerned about preserving the power in narrow near-diffraction-limited beams over long ranges many kilometers , which are accurately pointed and controlled to eliminate both platform jitter and atmospheric beam distortions.

This category of lasers was developed first, then laser power levels were gradually increased to the weapons class range discussed in the next section. The first laser range finder using ruby lasers was demonstrated less than a year after the laser's discovery and marked the introduction of widespread practical use.

As improvements in the technology, especially new laser materials, and new classes of lasers came along, both range and performance were greatly improved. Typically, a tank laser range finder is used to illuminate with great haste an enemy tank; the range is calculated from the received laser return pulse to determine the ballistic trajectory of a tank shell. The tank's gun is elevated and fired while the vehicle is moving.

The objective is to be faster than the enemy and to kill the enemy tank by delivering highly accurate munitions. With better laser materials, especially Nd: YAG neodymium-doped yttrium aluminum garnet, a crystalline solid with outstanding performance , field units have greater reliability and performance. In simplest terms the key to successful systems of this class is the capability to design, manufacture, and deploy lasers that are affordable and reliable. Early laser systems suffered from internal degradation of optics, which blocked their widespread deployment and required a major effort to resolve.

Even more years of development were needed to field other laser subsystems after the technical community sorted through thousands of options to find the right combination of power output, efficiency, reliability, and so on. Today, DOD generally utilizes the following:. D array pumped solid-state pulsed lasers for laser range finders, target designators, jammers, and so on; and.

The many thousands of battlefield range finders in tanks and designators for ground and aircraft were deployed using older flashlamp excitation or pumping of YAG in first-generation laser technology. New technology utilizes LDs to convert electrical energy into light energy for pumping solid-state crystals such as Nd: YAG with greater efficiency and reliability. In addition, many more applications have emerged for this type of laser that depend on the cost-performance trade-off.

The cost of LDs has been driven down by technology advances and volume manufacturing and is expected to drop even more. The sportsman will recognize this illuminator as the basis for the rifle spotting beam. Retrofit and upgrade of the entire class of pulsed range finder and target designator units so important to our success in delivering precision munitions in Desert Storm are proceeding.

Modern battlefield doctrine is, in fact, profoundly shaped by laser-guided bombs and missiles, enabled by our ability to cost-effectively make the approximately , reliable laser designator sources that have been fielded. Countermeasure lasers for jamming and sensor blinding require 1 to W, a range difficult to achieve until LD array pumped solid-state lasers became available. In combination with various wavelength shifting schemes [optical parametric oscillators OPO , Raman effect] to avoid sensor selective rejection filters, jammers and blinders constitute a new escalation in the "optical" battlefield.

It should be noted that Secretary of Defense Perry in September announced a prohibition against the "use of lasers specifically designed to cause permanent blindness of unenhanced vision and supports negotiations prohibiting the use of such weapons"—a position probably established, in part, because an eye safety device effective against all types of lasers generally found on the battlefield has not yet been developed and deployed.

However, the use of lasers for target destruction is still permissible. Air Force study New World Vistas 2 anticipates that this class of systems will be fielded in the next decade. Widnall and Chief of Staff Gen. It is interesting that early forecasts of the significant use of laser communications in free space have not materialized.

This status is due largely to technical problems with lasers combined with advances in the capability of competing microwave links. The better cost-risk trade-off of microwave links is described in Chapter 1. The maturation of LDs as a product seems likely to result eventually in fielded commercial links, especially in the 0. The concept of near instantaneous destruction of airborne and space-based targets is quite appealing. To this end, high-power lasers have been under development since the s. There have since been many technology advances in high-energy lasers, and both ground and airborne demonstrations have validated the basic weapons concept Figure 4.

Laser weapons designs and matching mission roles, such as the destruction of sensors in imagers, missile guidance, and surveillance systems, are understood well enough that advanced system development could proceed if national security required it Knowles, The New World Vistas 2 study advocates extensive use of laser weapons against missiles, satellites, and other ground assets in the next decade.

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Today a number of gases have been discovered with the right properties to generate high-power in the 1-MW regime and offer the flexibility of excitation by electrical or chemical means. Entirely new areas of physics and optics are encountered in this high optical power regime.

Technical challenges include the following:. Extracting diffraction-limited beams with high-efficiency from the laser cavity;. Delivering beam power on target via optical control to correct for beam distortions during propagation; and. Solving operational issues such as environmental factors and lethality for different target classes. At first glance, high-power lasers would seem to serve only military needs. However, advances in this technology have provided many other uses for scientific and commercial applications.

Courtesy of Lawrence Livermore National Laboratory. The distortion of optical beams along an atmospheric propagation path is highly complex. It is compounded by high-power nonlinear effects, which can also break up the beam. During the s and s, DOD mounted a major technical campaign to understand and resolve these problems.

In addition to elucidating the physics of beam propagation, adaptive optics and phase conjugation were developed to solve the problem. These techniques have been reduced to practice and are now employed as essential elements in system designs. Adaptive optics control of laser beams constitutes a major recent breakthrough in laser weapons system developments. Ground-based lasers can now potentially negate satellite threats. However, not all elements of the technology are complete. Continued developments are required in terms of power, size, weight, reliability, and beam quality.

Future activities should address reducing the manufacturing cost of high-power laser systems to make them more affordable. Adaptive optics is effective in this area as well, providing compensation for lower-cost, relaxed optical tolerance, laser resonator designs. Laser weapons can revolutionize battlefield strategies, but they raise a new class of system engineering and battle operational issues.

Knowing how and when to use this new capability takes careful planning. For example, the laser weapon must work in concert with existing defenses. A shipboard laser weapon with short time response may be the last line of defense against an incoming enemy missile that has. Many such issues, involving the agility of the laser weapon and targets in comparison with the allowable time for weapons use, are still unresolved.

The Anti-Ballistic Missile Treaty constrained work on space-based platforms with lasers designed for use against space targets. An airborne system is in active development that would intercept tactical theater ballistic missiles such as Scuds during their boost phase and blow them up via laser heating. This is an important deterrent since the munitions would be destroyed over enemy territory.

A compact chemical oxygen iodine laser COIL has been selected for this mission. This entirely new dimension in threat deterrence cannot easily be duplicated by other nations and underscores the breakthrough potential of optics to respond to national defense needs. Laser weapon technology and military needs seem to be converging in this decade.

As a result of the Air Force New World Vistas study, systems and operations analysts are very active in matching laser concepts to today's problems. For example, the notion of a "frugal kill" optimizes laser fluence on target to just the right amount for destruction without overdesigning the system. Fiber-optic FO systems represent an area in which commercial investment has led the way for DOD applications.

For DOD, desirable attributes include freedom from electromagnetic interference, low power consumption, small size and weight, enhanced physical security, and high available data transmission rates. The use of fiber optics on aircraft, satellites, ships, and submarines has proceeded at a somewhat slower pace as the design and mainte-. Digital FO communications are now used both to connect military communications terminals and within military facilities. The center of gravity of DOD development and use has been in the Navy, although the Army push to digitize the battlefield will bring more FO systems into play.

Air Force work has featured conventional systems for large ground installations and special FO links for aircraft and satellites. Much of this work has proceeded in parallel with the maturation of commercial FO networks. The extension of digital techniques into the terabit region, development of special sensors by the Navy, parallel and serial local area networks for avionics, and both backplane and chip-to-chip communication projects are under way. Other nondigital uses of fiber optics include the FO gyro discussed below and the propagation or control of radio-frequency RF signals via fiber, which is important because of the widespread military use of the RF spectrum.

Compared with atmospheric RF propagation, fiber offers the inherent advantages of ultrawide bandwidth and much lower propagation loss, but the laser must be modulated and the RF signal faithfully extracted at the receiver terminal. FO usually offers a lower-loss alternative to coaxial cable. At 30 to GHz it will probably prove to be superior to conventional waveguide or microstrip for which the propagation loss is prohibitive at long distances i. Today the technology is practical at 20 GHz for direct diode laser modulation and at 50 GHz for external modulation at higher cost , with further improvement to 30 and GHz expected within 10 years.

An oft-cited example of the effectiveness of this technology is the avoidance of antiradiation homing missiles launched by the enemy to disable the antenna by guiding on the outgoing radar signals.

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Remote placement of the antenna, enabled by low-loss FO transmission of RF signals, secures the safety of personnel and the field shelter housing the control equipment. FO permits a ''true time delay" phased array radar by switching lengths of fiber see Figure 4. This capability is not possible at. A grand challenge for military aircraft manufacturers is the development of conformal antennas for radar, communication, and electronic warfare. Integrating antennas into the airplane skin saves space and weight and improves the aerodynamic profile. To make this happen, the antenna beam patterns must be steered electronically.

Photonics offers a new approach to the vexing problem of building a compact, flyable, stationary antenna with an electronic beam steering mechanism. Fiber-optic elements of different length, which by themselves take up very little space, are the key to the solution. By switching in different lengths of optical fibers, the microwave signal phase can be adjusted to each phased array element and beam direction can be changed at will. This concept has been demonstrated, and efforts are proceeding to make a workable version for aircraft systems.

It had a wide spur-free dynamic range no extraneous signal channel noise nearly adequate to meet today's desired radar performance requirements.

Major Navy projects are well under way to use this technology to make order-of-magnitude improvements in surface ship antenna structures, with tests of readiness planned for There are no obvious technical impediments to further improvement of FO-RF technology. Widespread future use and high payoff to DOD are likely. In warfare, timely acquisition and distribution of information is essential. Military planners, very conscious of this basic tenet, are "digitizing the battlefield. The Air Force New World Vistas study calls for better cockpit displays to relieve overworked pilots; hence, display technology must keep pace with the means to rapidly process and analyze data.

Today, a small number of U. Pixel counts vary approximately from x to x , and most applications require full color. Both technologies had a goal of providing x monochrome pixels in approximately 1 square inch. Placing color filters on these elements provides a x color display. Production and device yield issues remain to be solved before fieldable hardware results. Displays utilizing these technologies are operable under high ambient light levels and can be made rugged for field use.

Newer FPD technology includes field emission, MEMS microelectromechanical systems , and three-dimensional displays requiring no viewing aids e. A consortium of manufacturers works on the HDS program in partnership with the government. The following results have been reported:. Efforts are being made to determine these products' producibility and develop manufacturing processes for them.

The major technology initiatives are described in detail below. Many other niche applications use optics to advantage, attesting to the many dimensions that this technology can bring to bear on solving specific problems. Examples include the following:.

The release of sarin in the Tokyo subway once again brought us face-to-face with the destruction and loss of human life that a small terrorist group can cause. Some believe that the open U. The Oklahoma City and World Trade Center bombings are reminders of our need for greater vigilance and better technology for early detection of this type of threat. Weapons of mass destruction involving nuclear, biological, and chemical NBC species are a significant new emerging global threat and have a high priority within DOD. Because chemical and biological weapons can be produced with relatively low technology and are easily acquired, their number is increasing.

More than 30 countries are now suspected of having chemical weapons capability and more than a dozen of having biological weapon competence. There are also about a dozen confirmed nuclear-capable countries. Electro-optic technologies are central to meeting mission area requirements arising from these threats. The technologies of interest include the following:. Active detection devices, such as backscatter lidars at eye-safe wavelengths, differential absorption DIAL lidars over the band between 2 and 11 mm, resonance Raman lidars, and laser-stimulated biological fluorescence;. Long-range chemical detection using lidar or other stand-off techniques would give the greatest tactical advantage.

An effective detection scheme must meet many practical mission requirements. The objective of achieving an ultralow species concentration detection capability is important, but what is also required is an extremely low rate of false alarms for detection for a wide range of chemical species.

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This places multidimensional requirements on the sensor suite, making electro-optics an essential part of strategies for addressing this threat. A well-planned, well-coordinated, cohesive effort is required to greatly advance the probability of success. This would include a multiyear strategy overseen by a strong single manager to coordinate activities within DOD, DOE, and so forth.

Laser gyros are important as inertial navigation sensors. These devices run laser light around in a closed path in both directions; if the platform rotates, the tiny differential time delay can be detected and the rotation rate deduced.

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Early gyros used helium-neon ring resonators, which oscillated at different frequencies; platform rotation is proportional to the differential frequency. With these parameters, a 4-pound, cubic-inch RLG is suitable for aircraft navigation. For other uses such as missile guidance, smaller, lower-accuracy units are necessary. Development of the fiber-optic gyro FOG has created another alternative, especially for lower-accuracy applications. A FOG with a size and weight of 1. These units are now in production as replacements for conventional mechanical gyros that have to be spun up for each mission.

Inertial guidance units are still necessary, even in this age of global positioning systems, since these systems can be jammed during wartime. Many signal processing functions can take advantage of the unique properties of optics. Mathematical calculations can be performed in real-time using analog optical techniques. Some computations are extremely tedious when performed on a digital computer but relatively easy on an analog optical computer. For example, Fourier transforms can be readily accomplished by placing a suitable lens in an optical telescope.

Since Fourier transforms are often used to obtain the frequency spread of short-pulse radar signals, an optical subsystem could provide an important capability. Image and electronic signal processing have long been fostered by research organizations within DOD, such as the Office of Naval Research.

Acousto-optic modulator-based signal correlators have been designed and incorporated into military products, although widespread field deployment has not yet occurred. Prototype vector-matrix, matrix-matrix, and neural network optical processors have all been applied to DOD problems with varying levels of success.

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