A directed-energy weapon (DEW) emits energy in an aimed direction without the means of a projectile. A DEW transfers the energy to a target for the desired effect. Most DEWs rely on electromagnetic waves or subatomic particles that impact at or near the speed of light. The energy can be delivered in various forms:
Electromagnetic radiation (e.g., radio frequency devices, microwave devices, lasers, and masers)
Particles with mass (e.g., particle beam weapons; theoretical, no known weapons exist)
Sound (e.g., sonic weapons)
Several of these weapons have already been tested in combat and are now potentially available to terrorists. As new technology becomes available and the military uses become apparent, terrorists will adopt it and often increase its lethality.
Whatever the form of electromagnetic energy used for the DEWs, they all share certain characteristics that make them revolutionary weapons:
They hit a target at the speed of light.
They are line-of-sight weapons.
The price of use is typically a small fraction of what it costs to fire a missile or a large gun. Low- and medium-power lasers can be cheaply obtained.
They are able to engage many different targets because of their instantaneous effects and the ease of reaiming them.
Immediately after the development of the first functional laser, the military (and hence terrorist) potential of the laser was apparent. Modern pulsed lasers can reach energy levels of up to millions of watts in a fraction of a second. In many cases, the laser is not intended as a weapon per se, but rather as a targeting device for another weapon, such as a missile or a “smart bomb.” The properties of the laser are particularly suited for this purpose. The military in many nations developed lasers for use as range finders and target designators. Laser light has special qualities, including the following:
The light released is monochromatic; it contains one specific wavelength of light (one specific color). The wavelength of light is determined by the amount of energy released when an electron drops to a lower orbit. This wavelength depends on the material of the laser and the method by which it was stimulated to emit light. The frequency of the wave multiplied by its wavelength equals the speed of light.
The light released is coherent . It is “organized”; each photon moves in step with the others (i.e., the waves of the electromagnetic radiation are in phase in both space and time). This means that all of the photons have wave fronts that launch in unison and the beam is parallel.
The light is directional . A laser light has a tight beam and is very strong and concentrated. A light bulb, on the other hand, releases light in many directions, and the light is weak and diffuse.
The light does not disperse over long distances because of the coherent nature (collimation) of the laser beam.
Military laser devices can easily cause retinal injury, even at a distance of many miles. Military planners found that this optical effect can be used as an antipersonnel system to actively disable personnel by blinding or “dazzling” them. By 1985, the British Navy had developed an unclassified weapon that was fitted aboard ships to blind oncoming enemy pilots at ranges up to 3 miles. Deployment of lasers designed specifically to blind is now banned by the Protocol on Blinding Laser Weapons, adopted by the United Nations in 1995. , Many thousands of target-designation and distance-ranging lasers have been manufactured and sent out with troops of multiple countries. Because of this availability, they may find their way into the hands of terrorists and be used against U.S. civilians.
Civilian lasers can be easily adapted to similar purposes. For example, muggers in England have used simple laser pointers to blind victims before robbing them. There have been many anecdotal reports of eye pain and headaches lasting for several weeks after brief ocular exposures to laser pointer beams. The pathology of this pain is difficult to understand, because lasting pain is not a common consequence of retinal laser treatment for diabetes, when a considerable amount of laser energy is delivered to the retina. ,
Lasers have already been used to blind helicopter pilots and commercial pilots. , It would be no great stretch for a terrorist to mount a relatively powerful laser on a truck or within a car and attempt to blind pilots who are landing at a commercial civilian airport. Likewise, simple lasers may destroy vision in law enforcement officers responding to a terrorist attack.
Long-term exposure to high-intensity microwaves can produce both physical and psychological effects on humans, including sensations of warmth, headaches, generalized fatigue, weakness, and dizziness. The effect depends on the power output of the weapon and the distance between the generator and the person. The U.S. Air Force has fielded a microwave system (Active Denial System, or ADS) that uses the surface heat production of high-power, very high frequency (VHF) microwaves to induce people to leave an area. The military currently has this weapon only mounted on a truck but is working on a more portable version.
The destruction of electronic devices by high-intensity microwave devices is well understood, and multiple weapons have been developed to exploit this vulnerability. These include the Bofors HPM Blackout, a commercially available electromagnetic pulse weapon. Smaller devices using similar technology have been proposed to disable vehicles in police chases.
The Long Range Acoustic Device (LRAD) was designed to “hail, warn, and notify” vehicles and sea vessels at a distance. It uses high-intensity, highly focused acoustic output to communicate beyond the effective range of small arms. LRAD’s main function is as a hailing device, being basically a super-bullhorn. But it can also be used in what has been termed a warning tone : an extremely loud and unpleasant sound said to resemble a fire alarm. Despite the device’s nonviolent purpose, media has termed it a sound cannon or sonic cannon . Extremely high power sound waves can disrupt or destroy the eardrums of a target and cause severe pain or disorientation. This is usually sufficient to incapacitate a person. According to the National Institute on Deafness and Other Communication Disorders, any sound over 90 dB can damage a person’s hearing, so the LRAD can damage hearing. Less powerful sound waves at certain frequencies can cause humans to experience nausea or discomfort. The use of these frequencies to incapacitate persons has occurred both in counterterrorist and crowd-control settings. There is no medical treatment for these effects except removal from the source. Although many popular writings have postulated acoustic weapons with internal effects such as cavitation of tissue, practical application appears to require higher energy than currently available.
Particle Beam Generators
A particle beam is a directed flow of atomic or subatomic particles. These high-energy particles, when concentrated into a beam, can melt or fracture metals and plastics. They also may generate x-rays at the point of impact. These weapons are in development stages only.
There is no foolproof countermeasure for a blinding laser. Each of the available protective efforts will hinder to some degree a person’s ability to see and to carry out activities requiring sight. , Laser radiation does not travel through opaque objects. Any opaque cover will provide protection against all but very high power military lasers. Avoid looking directly at any laser beam or its reflection, if at all possible. Reflections off shiny surfaces may cause damage, despite forward cover. Wearing an eye patch on one eye offers partial protection from blinding lasers; unfortunately, it also deprives the wearer of depth perception and peripheral vision. Patching only prevents blinding in the patched eye.
The present method of protection from the laser threat is quite simple: a pair of protective sunglasses can be fashioned that reflect the laser light but let other wavelengths through so that the wearer can see sufficiently to do tasks. These helmet visors or goggles would prevent laser radiation from damaging the wearer’s eyes. This works well if the laser threat has been previously identified and is limited to one or two wavelengths. However, there are multiple frequencies available in lasers; each additional frequency “protected” is a wavelength that is dimmed for vision. The management of casualties from the effects of laser light is discussed later in this chapter. The triage of these casualties can be accomplished by use of the triage algorithm shown in Fig. 81-1 . Casualties from consequent events, such as a blinded driver or pilot crashing his or her vehicle, are managed in the customary fashion covered by trauma protocols. There would be no difference in management of these casualties if they had a concomitant eye injury.
Key management issues
Laser Eye Injury
The eye is the part of the body most vulnerable to laser hazards. When a person is exposed to laser light, he or she can be temporarily blinded (as a result of dazzling), be blinded for a prolonged period of time (as a result of photolysis), or incur changes in visual function from cataracts, retinal lesions, or hemorrhages. This damage may be either temporary or permanent, depending on the wavelength and power of the laser. Because the eye is more sensitive and the pupil is larger during darkness, laser weapons have a greater effect at night than during the day. Eye damage can occur at much lower power levels than those causing changes to the skin, and ocular injuries are generally far more serious than injuries to the dermis. If the person is using a see-through optical device, such as binoculars, the beam strength is magnified and greater injury to the eye can result. Even modestly powered lasers can temporarily blind an unprotected human looking through a telescope or binoculars. Higher-power lasers can be used to destroy objects in flight or on the ground.
Examination of the eye in part depends on available tools. In the field, examination may be limited to direct vision with magnification supplied by loupes or magnifying glasses. Corneal injuries may be assessed with fluorescein staining and ultraviolet light. In the emergency department, further assessment with a slit lamp is appropriate, and if available, use of a retinal camera may be appropriate. If any abnormalities are found, referral to an ophthalmologist is appropriate.
Retinal damage primarily occurs in the 400- to 1400-nm wavelength range (i.e., in the visible and near-infrared [IR-A] region). Laser light between visible and the IR-A region can cause damage to the retina. These wavelengths are also known as the “retinal hazard region.” Radiation in these wavelengths is the most hazardous because it is transmitted by the optical components of the eye. The infrared spectrum is often used for military target-designation lasers. IR-A radiation is transmitted by the cornea to the lens of the eye, which narrowly focuses it on the retina, concentrating the radiant exposure of the laser by up to 100,000 times. It is this considerable optical gain of the lens arrangement of the eye that increases the hazard when laser beams enter the eye. In the retina, most of the radiation is absorbed in the retinal pigment epithelium and in the choroid, a dark brown layer with exceptionally large blood vessels and high blood flow rate. Because the tissue structures of the retina are unable to undergo any repair, lesions caused by the focusing of visible or IR-A light on the retina may be permanent. The most critical area of the retina is the central portion, which includes the macula and the fovea.
Damage to the retina or hemorrhaging from retinal damage can cause a complete loss of vision. Persons who see large dark spots at or near the center of their vision, who have a large floating object in their eye, or who have an accumulation of blood in the eye should be promptly evacuated to a hospital with ophthalmological support. There is no currently accepted treatment for laser- or light-induced eye injuries. However, hemorrhage into the eye noted on either direct examination of the eye or with a slit lamp should be treated by positioning the patient in a head-up position to allow the blood to settle into the lower part of the eye. Laser burns to the retina do not require an eye patch. Indeed, an eye patch may reduce the person’s remaining vision. A laser eye injury can worsen with time, so anyone with a suspected laser eye injury should be evaluated promptly and again at regular intervals.
Cornea and Lens
Laser light in either the ultraviolet (UV) or far-infrared spectrum can cause damage to the cornea or the lens. Selective, sensitive portions of cells in the cornea absorb UV light (i.e., 180 to 400 nm), resulting in photochemical damage. Many proteins and other molecules (such as DNA and RNA) absorb UV light and are “denatured” by the radiation. Excessive exposure to UV light can cause photophobia, redness of the eye, tearing, discharge, stromal haze, and other effects. These adverse effects are usually delayed for several hours but will occur within 24 hours. The lens principally absorbs UVA (315 to 400 nm). The lens is particularly sensitive to the 300-nm wavelength. XeCl excimer lasers operating at 308 nm can cause cataract with an acute exposure. The cataracts are delayed and may not occur for years.
Far-infrared radiation (IR-B) (i.e., 1400 nm to 1 mm) is produced by CO 2 lasers and is also absorbed primarily by the cornea ( Fig. 81-2 ). Thermal damage is caused by the heating of the tears and tissue water of the cornea by the infrared light. Excessive exposure to infrared radiation results in a loss of transparency of the cornea or surface irregularities. A high-energy laser pulse may severely burn or perforate the cornea. Severe burns or perforations should not be patched, and the eye should be protected to ensure that the vitreous humor does not leak out. Minor laser burns to the cornea may be treated with an eye patch and appropriate eye antibiotics. Some infrared radiation in the IR-A range (700 to 1400 nm) and the IR-B range (1400 to 3000 nm) is absorbed directly by the lens. These effects are delayed and do not occur for many years (e.g., cataracts).