Military
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
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