AAWSAP DIRD, State of the Art and Evolution of High-Energy Lasers, March 2010

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Introduction
The purpose of this report is to provide an overview of the current state-of-the-art and
potential evolution of megawatt (MW) class high-energy laser (HEL) weapons.
Implications for space vehicles in or beyond earth orbit will be addressed.
It is rare today to find an individual who doesn't have some concept of a laser weapon.
From Orson Wells's Martian invaders in War of the Worlds, who used them with chilling
efficiency, to the now-classic Star Wars movies, the capabilities attributed to such
devices have grown with time and with writers' imagination. While most fictional
depictions of laser weapons (and many news stories) are without sound basis, these
devices do offer the potential for a whole new class of weapons and capabilities which
may complement (but not replace) existing kinetic energy (KE) weapons and electronic
warfare.
BASIC ATTRIBUTES OF KINETIC ENERGY AND HEL WEAPONS
KE weapons (bullets, shells, missiles, bombs, and so forth) require a finite period of
time to reach the target but are then able to destroy it instantly. They can deliver
immense quantities of explosive energy and destroy large areas. This makes KE
weapons most effective at engaging hardened, large, or stationary targets. Collateral
damage concerns, such as a desired target next to a hospital, enemy forces near
friendly forces, or a sniper target in a crowd can significantly limit the opportunity to
use KE weapons. Randomly moving targets also present a challenge for KE weapons
due to difficulties in predicting the target's location at the future time of arrival or in
tracking the target with sufficient accuracy.
High Energy Laser (HEL) weapons, by contrast, begin delivering the laser beam's
energy to the target at the speed of light. However, they require a finite dwell time to
accumulate enough thermal energy (heat) on the aim point to achieve the desired
effect (similar to a blowtorch). The strength of an HEL weapon is its ability to precisely
deliver a limited quantity of energy to a small spot with little collateral damage to
nearby objects or people. The instantaneous measure of a focused laser beam's
effectiveness is called "irradiance" and is measured in power per unit area over the
laser spot (typically watts/cm2). The beam's ability to inflict damage, by heating during
a time interval, is called "fluence" and is typically measured in joules/cm 2. Fluence is
simply irradiance x time and one joule is equal to one watt for one second.
Speed-of-light energy transfer, coupled with precision tracking, allows HEL weapons to
efficiently engage softer targets which are highly maneuverable, only visible for short
periods of time, or at extremely long range. Although the initial cost of a laser weapon
might be high, the logistics trail is short and the cost per shot is comparatively
inexpensive since the only major expendables are laser chemicals or electricity.
Figure 1 compares the relative strengths and weaknesses of KE & HEL weapons for
different classes of potential targets. Just as there is a wide variety of KE weapons
(ranging from bullets to precision guided munitions to nuclear weapons) for different
types of applications, one could envision a range of future HEL weapons at different
power levels, wavelengths, weights, volumes, and costs which would be best suited for
specific applications.
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