A New Laser For War And
Peace Source: Space.com October 23, 2000
You've seen it all before: intense beams of energy
lancing out from attacking spacecraft, piercing tough, armored
plating. There's an explosion or two, maybe three. Soon, even the
generators that produce protective force fields will fail. The
defending vessel will detonate in a thunderous blossom of metals and
fuel.
But science fiction isn't real-world combat. On Earth,
military lasers have their problems, in particular because of the
atmosphere's tendency to absorb and diffuse focused light energy.
Now there may be a solution. A new breed of laser --
known as an FEL, or free-electron laser --- could finally overcome
several obstacles that currently confound deployment. Chief among an
FEL's attributes is tunability -- varying wavelengths of lased light
could be selected, even during operation. (Traditional, chemically
supplied lasers are set at one specific wavelength.) Like tuning to a
radio station, picking the right wavelength would make the difference
between a strong or weak pulse of energy directed at an incoming
target.
Spurring military interest in FELs and other types of
lasers is the worry about rogue nations developing and remotely
launching strategic and tactical nuclear missiles. The persistent
questions about laser weapons' dependability and costs that have
limited investment and their adoption are therefore not only being
revisited because of geopolitical necessities, but also being
addressed by the quickening pace of technological development.
The FEL injector is the source of electrons used to
produce laser light. Although it is similar in design to Jefferson
Lab's electron accelerator, it is much larger because much more
current is needed to produce laser light powerful enough to quickly
process large amounts of materials.
"There's been a lot of hesitation on the part of the
individual services to invest in lasers to bring them to the maturity
required for combat," said John Albertine, an independent technical
laser expert who once headed high-energy laser research for the U.S.
Navy. "It wasn't worth the dollars to spend on a technology that may
or may not pan out, especially if the defensive weapons you have are
sufficient."
"But missiles are expensive and laser fuel --- whether
it's chemicals or electricity --- is very cheap. Plus, lasers can get
energy to the target essentially instantly -- at the speed of light.
High-energy lasers are a unique, new class of weapon."
Deterring attack
One key difficulty facing laser deployment has been a
phenomenon known as thermal blooming. Although powerful at the point
of origin, and delivered at more than 186,000 miles (299,330
kilometers) per second, a laser's energy can be absorbed and diffused
even in relatively instant passage through the atmosphere. The
culprits are water vapor, sea spray, suspended particles like soils
and volcanic ash, as well as byproducts produced by the burning of
organic and inorganic materials.
Depending on exact conditions, an FEL has the ability to
mitigate some or most of thermal blooming's effects, in essence
delivering energy effectively and directly. FEL defensive capability
has led the U.S. Congress to recently approve a $15 million grant to
Thomas Jefferson National Accelerator Facility, or JLab, located in
the southeastern Virginia city of Newport News. Lab scientists and
engineers have created one of the world's most powerful FELs, and the
highest average-power FEL known to exist.
"Jefferson Laboratory has by far the highest-power
free-electron laser in the United States. The only other is at Los
Alamos, and that's a relatively small effort," said Elihu Zimet, head
of the Naval Expeditionary Warfare Science and Technology Department
at the Office of Naval Research. "From a scientific and technological
standpoint, their work is outstanding. They have some of the best
people [available] and have shown remarkable progress."
As an electron beam passes between the copper colored
magnets shown here, it changes directions. The poles of the magnets
alternate, so the electron beam is forced to wiggle up and down. Any
wiggling electric charge emits electromagnetic radiation. The type of
electromagnetic radiation produced depends on how quickly the charge
wiggles. Slower wiggles can make radio waves or microwaves, while
faster wiggles can make x-rays. The FEL's electron beam will produce
infrared light and a future upgrade will allow it to produce
ultraviolet light.
The congressional stipend will go to upgrade JLab's FEL
power more than 10-fold, from a current level of 1.72 kilowatts to
perhaps as high as 20 kilowatts. At 20,000 watts, the FEL will have
more than enough power to disrupt internal electronics or perhaps even
burn through fuel tanks. Even at lower energies, the device would
still work to deter attack.
"A 10-kilowatt FEL wouldn't effect a hard kill on a
missile that is first detected low on the horizon. Nothing would be
physically blown apart," Dylla said. "What you're after is disabling
the infrared sensors on an incoming missile to prevent it from
sneaking up your airplane tailpipe or blowing up your smokestack on
the ground."
The Navy, which is charged with overseeing aspects of
the upgrade, is keenly interested in a beefed-up FEL because of its
potential to disrupt missile-mounted guidance systems. And, unlike
competing systems, primarily chemical lasers, FEL lasers are
electrically driven, therefore requiring no resupply of consumables in
order to operate. Changeable weather poses less of a problem for the
FEL's infrared light which, when tuned properly, can pass more easily,
even through a turbulent atmosphere.
In the marketplace
What has attracted industrial interest to JLab's FEL is
its private-sector potential. Thus far, FEL proof-of-concept
experiments have included investigations of assisted chemical-vapor
deposition, a technique used to produce high-quality coatings and thin
films for electronics and micro-components, as well as the effects of
FEL processing on nylon, polyester and a class of materials known as
polyimides.
When FEL light is made to shine on a material like
fabric, it abrades the fabric's surface, making it softer or better
able to absorb smaller quantities of dye without losing color
intensity. Likewise, a carpet's surface could be treated with FEL
light to make it stain resistant. The manufacturing industry could
thus do away with most environmentally hazardous wet-chemical
treatments now used during production.
The FEL has the potential to substantially reduce the
cost of photovoltaic panels by boosting their light-gathering
capacity. Because the solar power industry has been slow to develop
because of relatively high manufacturing costs and inefficient
sunlight-to-electricity conversion, any significant improvement in
either panel production or energy efficiency could lead to a boom in
consumer demand.
A host of other FEL applications are also possible,
including treatment of packaging to make it more resistant to microbes
and food spoilage. The FEL could be used by companies that forge,
coat, treat and clean metals of all kinds and businesses that
micro-machine materials and parts, as well as semiconductor
manufacturers.
By September 2002, as the upgrade concludes, FEL program
manager Fred Dylla said interested parties in both the public and
private sectors should have a powerful new tool at their disposal. "It
's tunable, high-power; and the power is generated efficiently," he
said. "If you're looking at defense and industrial applications, those
are key."
by James Schultz
http://www.space.com/businesstechnology/technology/fel_001023.html