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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