DOW-UAP-D137, AAWSAP DIRD, State of the Art and Evolution of High-Energy Lasers, March 2010

This document is a Defense Intelligence Reference Document (DIRD), a technical reference format used by the Defense Intelligence Agency (DIA) to capture baseline knowledge on a specific topic for later analytic use. DIRDs are best understood as reference and synthesis products rather than as original research. It is one of 38 DIRDs produced under the Advanced Aerospace Weapon System Applications Program (AAWSAP) between 2009 and 2011. Because AAWSAP’s scope permitted a broad range of supporting topics, not every DIRD in the series directly concerns aerospace systems or future threat assessment. The following summary reflects the DIRD’s scope and framing at the time of writing and should not be read as implying current validation of the concepts discussed. This DIRD surveys the development of high-energy laser weapons and notes that, although lasers had already become important military tools for ranging, guidance, and other lower-power uses, true weapon-class systems remained limited by power generation, beam control, atmospheric propagation, and logistics. The report reviews major laser types along with the optical, tracking, and thermal-management systems needed to make them militarily useful. It argues that high-energy lasers can offer important advantages over kinetic weapons in speed, precision, and low collateral damage, especially against softer or fast-moving targets, while also emphasizing that practical deployment has long been hindered by hazardous chemical fuels, thermal blooming in the atmosphere, power-supply constraints for mobile systems, and waste-heat removal.

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Defense
Intelligence
Reference
Document
Acquisition Threat Support
31 March 20 10
ICOD: 1 December 2009
DIA-08-1003-019
State of the Art and Evolution
of High-Energy Laser Weapons
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State of the Art and Evolution of High-Energy Laser
Weapons
Prepared by:
Acquisition Support Division (DW0-3)
Defense Warning Office
Directorate for Analysis
Defense Intelligence Agency
Author:
AAP Person 79
Administrative Note
COPYRIGHT WARNING: Further dissemination of the photographs in this publication is not authorized.
This product is one in a series of advanced technology reports produced in FY 2009
under the Defense Intelligence Agency, Defense Warning Office's Advanced Aerospace
Weapon System Applications (AAWSA) Program. Comments or questions pertaining to
l
this document should be addressed to!AAP Person 1 AAWSA Program
Manager, Defense Intelligence Agency, ATTN: CLAR/DWO-3, Bldg 6000, Washington,
DC 20340-5100 .
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Contents
Summary.................................................................................................................v
Introduction ........................................................................................................... 1
Basic Attributes of Kinetic Energy and HEL Weapons ......................................... 1
Elements of an HEL weapon ............................................................................... 2
Laser Devices ......................................................................................................... 3
Laser Fundamentals ........................................................................................... 3
Chemical Lasers ................................................................................................. 5
Solid-State Lasers .............................................................................................. 6
Rod and Slab Lasers ........................................................................................... 7
Fiber Lasers ....................................................................................................... 8
Ultra-Short Pulse Lasers .................................................................................. 10
Free-Electron Lasers ........................................................................................ 11
Beam Control and Atmospheric Propagation of Laser Devices.............................. 12
Brief History of DoD Laser Weapon Research ....................................................... 16
Laser-Material Interaction ................................................................................... 20
Vulnerability of Spacecraft to Laser Radiation...................................................... 22
Projection of Future HEL Weapon Capability ........................................................ 23
Recommendations................................................................................................ 25
Sources of Further Information............................................................................ 26
Figures
Figure 1. Utility of KE and HEL Weapons ................................................................. 2
Figure 2. Elements of an HEL Weapon System........................................................ 3
Figure 3. Basic Laser Concept................................................................................. 4
Figure 4. Cylindrical Gain Generator for HF Chemical Space Based Laser ............... 5
Figure 5. Common Solid-State Lasers and Their Wavelengths ................................ 6
Figure 6. Incoherent Combination of Single Mode Lasers at the Target.................. 9
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Figure 7. Incoherent Combination of Single Mode Lasers in a Fiber Combiner ....... 9
Figure 8. Free-Electron Laser Wiggler .................................................................. 11
Figure 9. Elements of the 2 kW FEL at Thomas Jeffereson National Accelerator
Facility .................................................................................................. 12
Figure 10. HEL Weapon Basic Tracking and Pointion Controls .............................. 14
Figure 11. Sealite Beam Director ......................................................................... 14
Figure 12. Typical Atmospheric Absorption and Scattering in the Infrared .......... 16
Figure 13. Army Mobile Tactical Unit .................................................................... 17
Figure 14. Air Force Airborne Laser Laboratory .................................................... 17
Figure 15. Mid-Infared Advanced Chemical Laser................................................. 18
Figure 16. MDA Airborne Laser in a Boeing 747-400F .......................................... 19
Figure 17. The Advanced Tactical Laser C-130 Aircraft......................................... 20
Figure 18. Single Pulse Maximum Permissible Exposure ...................................... 22
Tables
Table 1. Laser Systems Irradiance Calculations ................................................... 25
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State of the Art and Evolution of High-Energy Laser
Weapons
Summary
The laser was invented in 1960, only 49 years ago, and (along with the light­
emitting diode) has evolved into an essential part of our modern every-day life
in ways that could not have been foreseen. On the military side, there have
also been incredible advances in laser and beam control technologies but no
deployment of any high-energy weapons. Many concepts have been developed
and pursued, only to be discarded or deferred owing to technical immaturity,
expected production cost, lack of apparent utility, or logistics concerns.
The most significant technical impediment to deployment may have been the
large quantities of expensive and hazardous chemicals that were required by
the only available high-average-power lasers. This is now changing with
recent advances in electrically powered lasers (both solid-state and free­
electron lasers). As these devices mature over the next few decades, they will
enable practical military weapons at power levels ranging from kilowatts to
megawatts. This evolution may be somewhat slowed or limited in the United
States if there are policy concerns about the use of new types of weapons or
about weaponization of space. As an example, the Department of Defense
developed a microwave device for crowd control, called Active Denial, which
has been shown to produce temporary pain without any injury. However, DoD
was precluded from deploying it owing to policy (not legal) concerns. Other
countries may not exhibit similar restraint, as evidenced by the open
marketing of laser-blinding weapons despite a 1980 Geneva Convention
prohibiting their development or use.
Space offers the ideal environment for laser beam propagation; there is no
atmosphere to either attenuate or spread the beam. As a result, large
distances could be bridged quickly, with range limited by the size of the
transmitting telescope and the potential damage mechanisms limited primarily
by the laser's output power. Initial spacecraft laser weapons are conceivable
within the next 20 years, with the potential for follow-on growth in laser
power and transmitting telescope size. Transmitting telescope size would be
limited by the spacecraft size and competing demands for weight and volume.
Laser power could grow to the megawatt range as solid-state and free­
electron laser technology matures, but the major limitation to a spacecraft's
weapon capability may prove to be its ability to generate and store the energy
required by the laser and to store and dissipate the resultant waste heat.
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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/cm2. 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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HEL and Kinetic Weapons offer complementary capabilities
Soft/Small/Fast Moving/tactical Missiles & Hardened or
E/O sensors Vehicles Satellites Large Area
(Dazzle or Destroy) Cell towers & comm nodes ICBMs Tanks
Target Target tagging Radar antennas IRBMs Armored vehicles
Types Fire starting Power grids TheaterBMs Bridges
Small UAVs Ceramic RF radornes Cruise missiles Buildings
Manpads MilitaryUAVs Satellites Groups of people
Individual persons
-----------------Ro-cke-ts,- ar-tille-ry- & -mo-rta-rs ------------ --------
- Increasing Laser Power or Increasing Range for Same Effect ---+
Laser Power
Laser
1 kW 10kW 100kW 111Ni
Weapon E Medium Difficult Impractical
-Eff-ec-tiv-en-es-s --a-sy- ------------------------------ -- ----
KE Impractical Medium Easy
Weapon if stationary Difficult If stationary
Effectiveness if isolated if isolated
----------------- ----- ----- ---- ----- ----- -----
Figure 1. Utility of KE and HEL Weapons
ELEMENTS OF AN HEL WEAPON
The purpose of an HEL weapon system is to place and maintain the focused laser beam
on a target aim point for sufficient time to cause the desired heating effect. To
accomplish this, the weapon beam is generated by the laser device, then shaped and
relayed to the input of a pointing telescope (Figure 2). Laser beam sensors and
steering mirrors are required to maintain the HEL beam centered as it traverses the
optical train. The pointing telescope, which typical ly sits on azimuth and elevation
gimbals, then expands the beam to the diameter of its primary mirror and focuses it to
the range of the target while an imaging system (which can use a separate telescope or
share the transmitting telescope) acquires the target, tracks it, and points the
transmitting telescope's beam at the desired aim point. If the HEL beam's propagation
path from the weapon to the target includes the earth's atmosphere, it can have a
significant deleterious effect. Absorption and scattering of the beam, which reduce its
strength at the target, are caused by molecular constituents of the atmosphere and
aerosols such as haze or dust. Additionally, atmospheric turbulence spreads the
focused spot and further reduces its effectiveness. All of these factors must be taken
into account when designing a laser weapon.
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High Power Laser High Power Optics Pointer I Tracker I Atmospheric Target
Device and Beam Shaping Target Designator Propagation
TRACKER
EXHAUST
Atmospheric,
absorption,
ENERGY SOURCE scattering,
and turbulence
Figure 2, Elements of an HEL Weapon System
Laser Devices
LASER FUNDAMENTALS
The term "Laser" is an acronym for Light Amplification by Stimulated Emission of
Radiation. It is a unique device that employs the quantum states of matter to store
and convert energy into electromagnetic radiation. The resulting radiation is referred to
as "coherent," meaning it is single wavelength or "monochromatic" and highly focusable
due to its well controlled phase. In its simplest form, any laser device can be viewed as
an "energy-conversion" box with one input and two outputs. The input is energy, which
can take a variety of forms (electricity, light, or a chemical reaction) depending on the
specific laser, while the two outputs are a coherent beam and heat (Figure 3). Since
the overall energy-conversion lasing process is considerably less than 100 percent
efficient, significant waste heat is generated which must be removed from the laser.
Inside the la