Lasers And Their Potential For Tactical Military Use AUTHOR Major David R. Mirra, USMC CSC 1988 SUBJECT AREA C4 EXECUTIVE SUMMARY The current uses of lasers on the tactical battlefield are for use as range finders, target designators, and guidance systems. With advances in technology it is apparent that use of the laser as a tactical weapon is far from science fiction. There are problems, however, due to size and weight that must be overcome. Laser applications will continue to be added to the battlefield as technical problems are overcome. The first use of the laser on the battlefield as an offensive weapon will be against light-sensitive targets to include the human eye. Lasers of different wavelengths can cause damage ranging from flashblinding to complete permanent blindness. The technology for this type of weapon exists today, and employment is easily possible within the next few years. The use of lasers as disintegration weapons of destruction is not in the near future. Size, weight, and power requirements are significant problems that need to be overcome. LASERS AND THEIR POTENTIAL FOR TACTICAL MILITARY USE OUTLINE As we move into the next decade, we are again on the verge of fielding additional "higher technology" weapons. The next generation of tactical battlefield weapons will include directed energy or laser weapons against men, electro-optical sensors, and other light-sensitive targets. I Types of Lasers and Associated Problems A. Crystalline Lasers 1. Ruby 2. Glass B. Gasdynamic Lasers C. Chemical Lasers II Military Applications A. Ground-Based B. Sea-Based C. Air-Based III Tactical Uses on the Battlefield A. Antipersonnel B. Blinding Sensors C. Physical Damage IV Conclusion LASERS AND THEIR POTENTIAL FOR TACTICAL MILITARY USE by Major David R. Mirra Throughout history, the advantage in warfare has always been on the side that could achieve the greatest concentration of firepower at the right place and time. At the battle of Crecy in 1346, for example, the powerful and rapid-firing English longbow won out over the crossbow. After routing the crossbowmen in the front ranks, the longbowmen made mincemeat of wave after wave of heavily armored French knights on horseback. Though outnumbered more than three to one, the English lost only 100 men of all ranks, while the French lost 10,000! With the introduction of gunpowder and steady improvements in the design and engineering of guns, the bow and arrow disappeared. By 1590, the bow and arrow was replaced with gunpowder, a "higher technology" improvement, providing the capability of greater concentration of firepower without loss of mobility. Gunpowder employed a more efficient physical principle: chemical combustion.1 As we move into the next decade, we are again on the verge of fielding additional "higher technology" weapons. The next generation of tactical battlefield weapons will include directed energy or laser weanons against men, electro-optical sensors, and other light-sensitive targets. Speaking in late 1981, Defense Advanced Research Projects Agency director Robert Cooper said that $2 billion was "an enormous amount of money...for what still remains an exploratory development program. Yet he added that "it's the collective judgement of high officials in the Pentagon that laser weapons present a high potential for payoff. There is a good chance that we will put a high-energy laser weapon system on the battlefleld."2 The word laser is an acronym for Light Amplification by Stimulated Emission of Radiation. Here is a 1975 description: The laser is really a simple device composed of an energy absorbing medium such as a ruby rod; an excitation source such as a flash lamp; a container or cavity to hold the laser medium and mirrors and lenses to direct and focus the laser beam. Operation of the laser begins when the power source is turned on and the excitation source pumps energy into the medium. The atoms which had been at rest in the medium, are raised into an excited state from which they soon drop back to their normal level. While dropping back to their normal state, the atoms give off light energy called a photon. The photon strikes another photon and so on until a chain reaction is caused. This chain reaction of photons grows until the laser light is finally emitted from the medium. The output can then be focused and directed as a pencil thin beam of laser light.3 TYPES OF LASERS Since this early definition, tremendous advances in research and technology have taken place. In the ruby laser mentioned above, synthetic ruby crystals are utilized as the energy absorbing material. This medium is not efficient, as only about 1% of the light that goes into the rod emerges in the form of laser light. Most of it ends up in the form of heat, which must be removed or its effects on the laser rod may break up the beam or damage the rod itself. The heat removal required in ruby and other crystalline or glass lasers poses a serious problem. Although the external light source efficiently deposits energy throughout the transparent rod, the excess heat is much slower in leaving the solid. This fact, combined with some complications due to energy levels in the material, limits operation of the ruby laser to no more than a few pulses per second except at very low power levels, and also sets upper limits on the practical output power. Crystalline or glass lasers are easier to cool, and can produce much higher peak power, but they are not practical from a military tactical standpoint. They can only produce about one shot per day, due to heat dissipation problems.4 For continuous operation at high power output, a laser material that can quickly dissipate residual heat is necessary. Much research has been done with gas lasers; however, military uses for gasdynamic lasers are limited. The atmosphere does not transmit the beam well, and there is very little tolerance for error in design or manufacture of critical components. The size and complexity of gasdynamic lasers have little tactical application on the battlefield. Most demonstrations of laser weapons in the works involve the chemical laser. As its name implies, it derives its energy from a chemical reaction, the combination of hydrogen and fluorlne to produce molecules of hydrogen fluoride-in a vibrationally excited state. The term "chemical laser' usually refers to a hydrogen fluoride laser. The reaction in a chemical laser can be triggered by an electrical discharge. The starting point is a fuel containing hydrogen and an oxidizer containing fluorine. Because of problems with fuel stability, however, substitute fuels are frequently used. The laser beam is produced through a chemical sort of chain reaction. There are some drawbacks. The cavity into which the laser gas flows must be kept at a very low pressure, typically 1% or less of atmospheric pressure. There must be a way to get rid of the gas after it is passed by the laser mirrors. For a space based laser system, it could simply be vented outside. On the ground, however, because of atmospheric pressure, a vent must let the air in. This is necessary since hydrogen fluoride is toxic in concentrations of as little as three parts per million. The Army is currently working on methods to pack the waste hydrogen fluoride into canisters to prevent inadvertent venting into the air.5 From a military point of view, chemical lasers have some major advantages over gasdynamic types. One is that energy can be stored more compactly in the chemical form. On a battlefield, where portabillty is the key to moving quickly, ease of storage is a must. Another advantage is the shorter wavelength produced by the chemical laser. The short wavelength creates a smaller focal spot on the target with more concentrated energy. This shorter wavelength, however, creates the need for more accurate optics. There appears to be no free lunch in military application of laser beam technology; however, from research being done in the field, military applications seem to be unlimited. MILITARY APPLICATIONS Currently, military missions for laser weapons fall into two traditional military categories: tactical and strategic. Tactical weapons are those intended for use in battles between armed forces on the ground, at sea, or in the air. These weapons operate over short distances measured in terms of kilometers, miles, or nautical miles. Strategic weapons are intended for use against other targets, such as arms factories, logistics installations, or for defense of such strategic targets against enemy attack. Satellites, intercontinental ballistic missiles, and long-range bombers are considered strategic armaments; rifles, helicopters, short-range missiles, and most fighter aircraft are considered tactical. Nuclear weapons may be either strategic or tactical; high yield bombs are intended for strategic use, while low yield nuclear explosives are intended for tactical use. Tactical uses of ground-based laser weapons are being pursued by the Army. Research is being conducted on the feasibility of placing a moderate or high-powered laser into a tank or other heavily armored vehicle. These ground-based lasers would operate over ranges of a few kilometers under extremely demanding conditions, including being subject to dust, dirt, smoke, and enemy attack. The laser weapon could be used against anything that moved on or flew above the battlefield. Lasers could destroy targets by causing mechanical damage, triggering explosions of fuel or munitions, or knocking out enemy sensors. They might be used to blind soldiers, temporarily or permanently. It will be some time, however, before there is enough laser firepower designed to incinerate individual soldiers. It is simply not cost effective - bullets are cheaper. Clearly, directed energy weapons need not burn a hole through you; they need only blind or dazzle your eyes or electro-optic sensors to make you more vulnerable to the conventional weapons populating the battlefield."6 The Navy has considered putting laser weapons on ships to destroy attacking missiles - hopefully faster and more effectively than conventional weapons. The PHALANX Gatling gun system now in use can fire 6,000 rounds per minute, but that might not be enough to blunt a cruise-missile attack. The operating environment of these sea-based lasers is also demanding. Salt water and humidity present a difficult problem to overcome. Compactness of the system is not as critical an issue as for ground or air-based systems. Aircraft carriers can easily accommodate larger laser systems. The Air Force is studying the feasibility of putting laser weapons in planes to defend against missile attack and against other aircraft. The biggest problem is bulk and weight; a laser weapon can't defend a plane unless it can fit inside one. The Air Force would like to put lasers in fighters, but because of size and weight, bombers might be more practical. The strategic use of the laser falls into two research categories: near-term research in antisatellite weapons and long-term efforts to develop a system for missile defense - also known as the Strategic Defense Initiative (SDI). The military role of satellites particularly in surveillance, arms-control verifications, and communications, has made them potential military targets. The sensitive optics on these satellites are vulnerable to an overload of light, and easy targets for laser attack. The SDI lasers that are currently on the drawing board represent the most significant role ever proposed for laser technology. Lasers would be used to blunt an enemy nuclear missile attack and according to President Reagan on 23 March, 1983 "...would render nuclear weapons obsolete."7 TACTICAL USES OF LASERS ON THE BATTLEFIELD ANTIPERSONNEL "The ways in which beam weapons might be actually used against soldiers bear no resemblance to the near-instantaneous incineration envisioned by H.G.Wells in The War of the Worlds or to the instantly fatal death rays of pulp science fiction."8 Although the technology exists to melt soldiers with intense laser beams, the large systems necessary on the battlefield would make the systems impractical. Highly charged particle-beams could kill soldiers, but it would be akin to shooting flies with a TOW missile. A tightly focused laser beam could burn the skin, but would hardly be an efficient way to burn a man to death except at near point blank range. One part of the body, however, is quite vulnerable to laser light: the eye. The eye is vulnerable because it is similar to other types of optical sensors: it is extremely sensitive to light. This sensitivity varies widely with wavelength and is highest at visible wavelengths. Staring directly at the sun, or directly into a laser beam carrying only several thousandths of a watt of visible light can cause permanent damage to the retina. This occurs because the lense of the eye focuses visible and near infrared light, concentrating its power to high enough levels to burn the retina. Higher powers take less time to cause damage, with short, intense pulses being particularily dangerous. The result is not total blindness, but partial obstruction of vision due to "blindspots," which may be permanent or temporary depending on the power of the laser. "The type of physical injury that a laser can cause depends on the laser power, pulse duration, and wavelength. The wavelength is particularily critical in determining what type of eye damage, if any, will occur. Light with wavelengths between about 0.4 and 1.4 uM, (.0000014m) in the visible and what is called the near infrared regions, can penetrate the eyeball. The lens focuses this light to a pin point on the back of the retina which will cause bleeding and a permanent blindspot."9 Light at shorter and longer wavelengths can penetrate the eye slightly, but much longer and shorter wavelengths cannot. Light that can't penetrate the eye can still cause damage. Intense ultraviolet light can cause a variety of problems, including temporary blindness and a form of damage to the cornea that is similar to sunburn. The cornea burn depends on total exposure with little sensitivity to how fast or slow the exposure occurred. Like sunburn, the effect typically takes a few hours to show up. Long exposures to long-wavelength infrared light such as that produced by a chemical fluoride or carbon dioxide laser can also burn the cornea. The eye's natural blink reflex provides a safety mechanism because infrared intensities high enough to cause damage to the cornea, also cause pain. Continuous laser powers of more than 10 watts/cm2, roughly the intensity of a 100,000w beam focused to a 1m spot, would be needed to damage the cornea before the eyelid could shut, Once the eyelids closed, the absorption of the skin would prevent long infrared wavelengths from reaching the eye.10 This intensity is possible on the battlefield. Aside from permanent eye damage, temporary flashblindness presents a serious problem on the tactical battlefield. This occurs any time a bright flash of visible light dazzles the vision of the receiver. Dazzling can occur by staring directly at light brighter than the noonday sun, or by illuminating an extremely bright flash in one's direct line of sight. Anyone who has been on the receiving end of a flashbulb has no doubt experienced this form of vision impairment. Consider the effect on a helicopter pilot flying a night mission at 50 ft. The protection against laser effects is being studied. There are some simple measures that currently provide protection against laser effects. Ordinary clothing and in the future some type of aluminum-foil armor may be used as body protection. Special safety goggles have been developed that absorb laser light at certain wavelengths. The problem on the battlefield is that you don't know what type of laser you'll be facing. Even then, changing the wavelength is a simple matter of turning a dial. There are goggles that protect against all wavelengths. Unfortunately, the wearer can see no visible light due to the darkness of the glass.12 I don't see lasers being developed within the next ten years as antipersonnel weapons to be carried by individual fighting men. The day of the "ray-gun" is not yet here for two reasons. First, a laser "ray-gun" for use as a soldier's individual weapon currently presents little advantage over a conventional weapon. Both are line of sight weapons requiring visual, straight-line, target acquisition. There is no cover or concealment advantage; the soldier must still physically see his target to kill it. Secondly, current technology still requires that lasers be of considerable bulk and cost. This virtually eliminates the laser as an individual weapon. In the antipersonnel role, lasers may be centrally located, and easily used to blind or flashblind enemy personnel. BLINDING SENSORS "The priorities on the battlefield make electronic eyes more inviting targets than human ones."13 Many of our modern weapons rely on sophisticated electro-optical sensors. Laser attacks on battlefield sensors can be accomplished by several means. The first is by blinding sensors with modest power laser beams, which would cause them to lose track of what they were observing. If the sensor is guiding a weapon to its target, such blinding could cause it to miss. Another way to attack a battlefield sensor would be to confuse the sensors that trigger the explosion of a warhead on a missile or bomb. This could either cause a premature explosion that does not harm the target or prevent the warhead from exploding at all. One other way to disable a battlefield sensor is to cause thermal or physical damage to the sensor itself or to the optics that focus light onto it, again leading to a miss. The emphasis on lasers used against sensors is not so much physical damage, but rather damage to its electronic eyes. Most sensors are designed to operate over a limited range of wavelengths and light intensities. Generally, the longer the wavelength and the greater the sensitivity, the more vulnerable the sensors are to laser attack. Sensors of visible light are usually made of silicon and tend to be rugged. The most vulnerable sensors are those designed to detect thermal radiation from ordinary objects at room temperature. A Forward Looking Infrared Device (FLIR) operates in this spectrum. Other infrared sensors, those operating at shorter wavelengths, are used in heat-seeking missiles. An infrared laser could be used as a decoy to steer the missile along the wrong path, or could burn out the sensor, blinding the missile completely. With sensors used in large numbers on the battlefield, they are particularly vulnerable to laser attack. Unlike the human eye, however, electro-optical sensors can be more easily "hardened" against the laser threat. With appropriate filters and circuitry electro-optical devices can be designed to minimize laser damage. PHYSICAL DAMAGE A high energy laser is expected to take somewhere between a second to several seconds to do enough physical damage to kill a target. An intense beam could do the job in a short pulse, if the beam could make it through the atmosphere. A physical "kill" of a piece of equipment does not necessitate the total disintegration of the target. A laser focussed on the wing of an aircraft could produce enough heat to cause the fuel tanks to explode. Helicopter rotor blades and fuel tanks are also vulnerable. Because much higher intensities are needed to cause mechanical damage than to zap human or electronic eyes, physical damage is harder to produce. As laser beam intensity in the atmosphere increases, harmful atmospheric effects begin to manifest themselves. High energy laser beams are liable to be bent away from their targets or dispersed by thermal blooming effects in the atmosphere. The solution to these problems is certainly within current technological capabilities. The military "destructor beam" definitely is in our future tactical arsenal.14 CONCLUSION We stand at the verge of a revolutionary phase in the development of weapons for modern warfare. Lasers are the leading edge of the new group of directed energy weapons. Our current uses of lasers on the battlefield have thus far been limited to range determination, target designation, and missile guidance. As has been pointed out, however, the laser is capable of much more on the battlefield. Based on today's technology I don't see the military becoming totally reliant on lasers as a substitute for conventional weapons any time soon. I do see the laser coming into wider use as a complimentary weapons system within the next twenty years. The additions of new-purpose laser weapons will not occur overnight. The first new generation weapons will target the human eye, as that presents the softest target especially during night operations. "At night, the eye reacts automatically to lower ambient light by opening up and gathering in more light. But in doing so, the eye also increases its vulnerability to laser beams because more energy is permitted into the eye and is focused down onto a small spot on the retina.... At higher powers, light receptor cells are literally blown off the retina, permitting blood to leak into the eye causing swelling and often shock."15 Our first priority in defensing against the next generation of laser weapons should be toward the development of eye protection for all wavelengths of lasers. A blind soldier, sailor, airman, or Marine is as good as dead in a fast moving tactical scenario. As laser technology grows it is clear that the laser's role on the tactical battlefield will greatly expand from present day uses. FOOTNOTES 1 The Scientific Staff of the Fusion Energy Foundation, Beam Defense, Aero Publishers, Inc., Fallbrook, Ca., 1983,p. 26-27. 2 Robert Cooper, talk at Electro-Optical Systems and Technology Conference, October 1981, quoted in Laser Report, October 12, 1981, p.2. 3 Badolato, E.V., Tactics vs. Technology, Command and Staff College, Quantico, Va. 1974. 4 Hecht, Jeff, Beam Weaoons The Next Arms Race, Plenum Press, New York and London, 1984, p.65. 5 Svelto, Orazio, Principles of Lasers, Plenum Press, New York, 1986, pp.247-250. 6 MajGen Ray "M" Franklin, "Directed Energy Weapons," Marine Cords Gazette, July, 1987, p.21. 7 Presldent's speech on military spending and a new defense, 23 March 1983. 8 Hecht, p. 268. 9 Sliney, David, and Walborst, Myron, Safetv with Lasers and Other Optical Sources, Plenum Press, New York, 1980, pp.116-144. 10 Ibid pp.144-149 11 MajGen Franklin, p. 23. 12 Sliney and Walborst, p.151. 13 Hecht, p.275. 14 Hecht, p.278. 15 MajGen Franklin, p.23. BIBLIOGRAPHY 1. Badolato, E.V., Tactics vs. Technoloay, Command and Staff College Research Paper, Quantico, Va. 1975. 2. Cooper, Robert, talk at Electro-Optical Systems and Technology Conference, October 1981, quoted in Laser Report, October, 1981. 3. Franklin, Ray "M", MajGen USMC, "Directed Energy Weapons," Marine Coros Gazette, July 1987. 4. Hecht, Jeff, Beam Weapons The Next Arms Race, Plenum Press, New York and London, 1984. 5. President's speech on military spending and a new defense, 23 March 1983. 6. Scientific Staff of the Fusion Energy Foundation, Beam Defense, Aero Publishers, Inc., Fallbrook, Ca. 1983. 7. Sliney, David, and Walborst, Myron, Safety with Lasers and other Optical Sources, Plenum Press, New York, 1985. 8. Svelto, Orazio, Principles Lasers, Plenum Press, New York, 1986.
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