DOW-UAP-D137: State of the Art and Evolution of High-Energy Lasers - Chemical Fuels, Waste Heat and the Road to Electric Laser Weapons

Source file: DOW-UAP-D137_AAWSAP-DIRD-State-of-the-Art-and-Evolution-of-High-Energy-Lasers-March-31-2010.pdf Originating agency: Defense Intelligence Agency (DIA), Defense Warning Office, AAWSAP program Document type: Defense Intelligence Reference Document (DIRD), "Acquisition Threat Support" series; control number DIA-08-1003-019 Date: 31 March 2010 (information cutoff date, ICOD: 1 December 2009) Classification: UNCLASSIFIED//FOR OFFICIAL USE ONLY (the FOUO marking is struck through; released to the public in 2026) Page count: 31 VIRIN: 260918-D-D0360-1126 PURSUE Release: 6

Summary

This is one of the technical reference reports (DIRDs) that the Defense Intelligence Agency produced under the AAWSAP program. It is titled "State of the Art and Evolution of High-Energy Laser Weapons", dated 31 March 2010, and was prepared by the Acquisition Support Division (DWO-3) of the Defense Warning Office, in the DIA's Directorate for Analysis. The author's name is redacted and replaced with the label "AAP Person 79".

The report's stated purpose is "to provide an overview of the current state-of-the-art and potential evolution of megawatt (MW) class high-energy laser (HEL) weapons", with attention to the implications for space vehicles in or beyond earth orbit. It proceeds in a fixed order: kinetic versus laser weapons, the families of laser devices, beam control and atmospheric propagation, the history of DoD laser research, laser-material interaction, spacecraft vulnerability and a projection of future capability, ending with recommendations and sources for further reading. The body contains 18 figures and one table.

The bottom line is plain: despite striking progress in laser and beam-control technology, no high-energy laser weapon had been deployed. The most significant technical impediment, in the author's view, was the large quantity of expensive and hazardous chemicals required by the only lasers that had reached high average power, and that is changing as electrically powered lasers mature.

The paper does not mention UFOs, UAP or unidentified aerial phenomena. Its only brush with aliens is literary: the Martian invaders of "War of the Worlds" and the "Star Wars" films, which the author uses in the opening to separate fiction from physics.

Research Article

A reference document in the AAWSAP series

The cover shows the DIA seal, the series line "Acquisition Threat Support", the date 31 March 2010, an information cutoff date (ICOD) of 1 December 2009 and the control number DIA-08-1003-019. Page 2 carries an "Administrative Note" stating that the product is "one in a series of advanced technology reports produced in FY 2009" under the Defense Warning Office's AAWSA Program. Comments and questions are to be addressed to "AAP Person 1", AAWSA Program Manager, at ATTN: CLAR/DWO-3, Bldg 6000, Washington, DC 20340-5100. The note also carries a copyright warning: further dissemination of the photographs in the publication is not authorized. The text itself dates its own writing: the Summary says the laser was invented in 1960, "only 49 years ago", which places the drafting in 2009.

Of the 12 technical areas defined in the program's Statement of Objectives (DOW-UAP-D110), the report serves armament first and foremost. It also touches power generation (prime power and heat rejection), materials (laser hardness), human effects (eye damage) and structure (penetration of a pressure hull). Its angle is two-sided: the laser as a future weapon, and the exposure of future spacecraft to one. It repeatedly flags the foreign context, noting "many open literature reports of similar work in Russia, China, and other countries", and saying of slab lasers that much of the relevant research is occurring outside the United States.

Laser versus kinetic weapons: irradiance, fluence and dwell time

The opening chapter sets out the basic difference. Kinetic weapons (bullets, shells, missiles, bombs) take time to reach the target but then destroy it instantly. A laser begins delivering energy at the speed of light but needs a finite "dwell time" to heat the aim point, "similar to a blowtorch". The author defines two quantities that run through the whole report: irradiance, power per unit area in watts/cm2, and fluence, the accumulated energy in joules/cm2, which is simply irradiance multiplied by time.

Figure 1 places four classes of target on a power axis running from 1 kW to 1 MW. Soft, small and fast targets (electro-optical sensors, small UAVs, MANPADS) are "Easy" for a laser and "Impractical" for kinetic weapons. Moving tactical targets (vehicles, radar antennas, power grids, rockets, artillery and mortars) need around 100 kW. Missiles and satellites are "Difficult" at the megawatt level, while hardened targets such as tanks, bridges and buildings are "Impractical" for lasers and "Easy" for kinetic weapons. The recurring conclusion is that lasers may "complement (but not replace)" kinetic weapons. Their economic advantage is a short logistics trail and a low cost per shot, since the only major expendables are chemicals or electricity.

Four families of lasers and the megawatt barrier

Chemical lasers. "To-date, every laser which has been scaled to MW-class average power falls in the chemical category." The carbon dioxide laser (10.6 microns) reached high power around 1970, followed by the deuterium fluoride (DF, 3.8 microns) and hydrogen fluoride (HF, 2.8 microns) lasers in the mid-1970s. They "resemble rocket engines", the report says, because they combust a fuel with an oxidizer. DF was the Navy and Army choice for tactical development, HF was chosen for the Strategic Defense Initiative's Space Based Laser, and the Chemical Oxygen Iodine Laser (COIL, 1.315 microns) was chosen for the Missile Defense Agency's Airborne Laser. Only 10 to 20 percent of the reaction energy becomes laser light; the rest is heat carried away in the exhaust. Beyond about 10 MW the quantity of chemicals makes the concept "highly impractical" in space and extremely cumbersome on the ground.

Solid-state lasers. These need only electricity (plus cooling). The report calculates that a 5-second run of a 15 percent efficient 100 kW laser would require less than one kilogram of gasoline or diesel fuel, which makes "an extremely deep magazine" possible. The problem is heat that accumulates in the glass gain medium and can distort the beam or even crack it. The report cites Northrop-Grumman's Joint High-Power Solid-State Laser (JHPSSL), which produced 100 kW with good beam quality, and expects affordable, rugged, MW-class slab lasers within 20 years.

Fiber lasers. A fiber laser is "a rod laser which has been stretched many meters" to the thickness of a human hair, to shed heat. Single-mode fibers with stable polarization had demonstrated a few hundred watts, with a damage upper bound thought to be about 10 kW. Coherent combining requires bandwidths far below 1 GHz and phasing to about a tenth of a wavelength. Incoherent combining of 25 to 50 fibers had produced 50 kW, but with an effective beam quality of about 30, far from the diffraction limit. The forecast: militarized 50 to 100 kW devices within 15 years, and megawatt systems within 20 to 30 years.

Ultra-short pulse and free-electron lasers. Femtosecond lasers emit pulses shorter than a picosecond, with peak powers from a terawatt to a petawatt but average powers typically below a watt. Other than sensor damage, "the military potential of these devices is yet to be determined." The free-electron laser (FEL) accelerates electron bunches to nearly the speed of light and passes them through an alternating magnet array, the "wiggler", so its wavelength can be chosen by design. Figure 9 shows a 2 kW FEL at the Thomas Jefferson National Accelerator Facility; the highest average power FEL to date was 10 kW.

The atmosphere as obstacle: beam control and thermal blooming

The minimum spot area on the target is set by diffraction at approximately (R times lambda over D) squared, where R is the range, lambda the wavelength and D the diameter of the pointing telescope. It can only be improved by shortening the range, using a shorter wavelength or enlarging the telescope. In practice only about half of the laser's output reaches the spot, and jitter, turbulence and thermal blooming enlarge it further. The report explains the tracker, the Inertial Reference Unit (IRU) and the 1980s solution embodied in the Sealite Beam Director (SLBD), in which the IRU was loosely mounted inside the telescope and small fast steering mirrors stabilized the beam itself.

The lower atmosphere scatters and absorbs: "as much as 50 to 75 percent of a laser beam's energy can be lost over a 10 km lower atmosphere path on a fairly clear day." Absorption depends strongly on wavelength, with low-absorption windows around 1, 1.2, 1.6 and 2.2 microns. At high power the air in the beam path heats and defocuses the beam, which is thermal blooming. According to the report this was a key reason the Navy abandoned DF lasers for shipboard self-defense, and since no megawatt laser existed at the window wavelengths, the Navy began developing the tunable FEL.

Five decades of tests

The history chapter summarizes the American effort. By the mid-1970s the Army had placed a 50 kW carbon dioxide laser with a 40 cm beam director in a tracked vehicle, the Mobile Tactical Unit, and shot down small drones. The Air Force put a larger laser in a KC-135, the Airborne Laser Laboratory, and by the early 1980s had shot down air-to-air missiles such as the AIM-9. In March 1978 a multi-hundred-kW Navy/ARPA DF laser destroyed TOW anti-tank missiles in flight. In the mid-1980s the MIRACL laser and the SLBD were installed at White Sands Missile Range as the nation's first MW-class HEL weapon test bed, engaging subsonic drones, multi-mach missiles and strapped-down ICBM boosters.

President Reagan's 1983 "Star Wars" speech led to the Strategic Defense Initiative and HEL programs that peaked at a billion dollars a year, but they "did not result in the fielding of any weapons or major demonstration systems." The sole surviving MDA laser program was the Airborne Laser, at $200M to $500M a year over the preceding decade, which aimed to place a MW-class COIL in a Boeing 747-400F for boost-phase intercept. At the time of writing all three services were developing 100 kW-class solid-state lasers against UAVs, rockets, artillery, mortars and swarming boats, and the Air Force and SOCOM had installed a chemical laser test bed in a C-130, the Advanced Tactical Laser, to evaluate the utility of adding a laser to the AC-130J gunship.

Materials, eyes and spacecraft

A material's laser hardness is expressed by the parameter "W", in joules/cm3: the energy needed to melt or remove one cubic centimeter. Because specific results are usually classified, the report offers only general observations. Metals under aerodynamic load or pressure fail by crack propagation well before burn-through; fiberglass-epoxy composites fail by ablation and delamination; ceramics, "similar in composition to common Corning Ware", shatter under thermal shock, and a thick piece fails at almost the same levels as a thin one.

On the eye the report debunks a myth: there are no "eye safe" wavelengths. Wavelengths out to about 1.2 microns are focused on the retina and leave blind spots; those from about 1 to 1.5 microns are absorbed in the ocular fluid; those longer than about 1.5 microns are absorbed in the cornea and cause scarring. Figure 18 plots ANSI Maximum Permissible Exposure values.

The spacecraft chapter lists three vulnerabilities: whole-body thermal failure of a craft that must stay fairly close to 70 degrees F, either by altering the absorptance/emittance ratio of its surface or by "flood-loading" it with megawatts during a few-minute pass over a ground site; exposed components such as solar panels, antennas and star, sun or horizon sensors; and penetration of a crewed pressure hull.

Significance

Within the AAWSAP DIRD series this is one of the most conventional papers: an engineering survey of real technology with no speculative physics. It was written days before two neighbours in the series, DOW-UAP-D138 on warp drive (2 April 2010) and DOW-UAP-D139 on wormholes (6 April 2010), and the contrast shows the breadth of the program, from achievable engineering to remote theoretical physics.

Its distinctive contribution is the projection chapter. The author estimates that an electric laser with a 25 percent "wall plug" efficiency would need at least 4 MW of electrical power for a 1 MW beam and would shed 3 MW of waste heat, and that an FEL would need about a megawatt of continuous power just to refrigerate its niobium accelerator cavity with liquid helium at 2 K. Hence the report's key sentence: storing and removing heat may be harder than generating the power. Table 1 computes space-based irradiance for a 1-micron laser, a 1-meter telescope and a beam quality of about 1.5, ranging from 0.1 kW/cm2 on a 50,000 cm2 spot (10 MW at 1,000 km) to 10 kW/cm2 on 5 cm2 (100 kW at 10 km); a 3-meter telescope would triple the range. On an arithmetic check, the spot areas printed in the two 350 km rows (500 and 50,000 cm2) do not agree with the irradiance column or with the report's own scaling rule; both appear to be meant as 5,000 cm2.

Other caveats: the report relies on open sources and points readers to DEPS, SPIE and AIAA conferences; it attributes the invaders of "War of the Worlds" to "Orson Wells", a blend of the novelist H. G. Wells and Orson Welles, who adapted the book for radio; at one point it cites Figure 4 where Figure 5 is meant; and it says other countries openly market laser-blinding weapons "despite a 1980 Geneva Convention". The explicit ban on blinding laser weapons was added to that 1980 convention as a separate protocol only in 1995, a distinction the report does not draw. It also notes that DoD was precluded from deploying the Active Denial crowd-control system "owing to policy (not legal) concerns."

Key People

Locations

Key Concepts

Notable Quotes

"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." -- page 5

"On the military side, there have also been incredible advances in laser and beam control technologies but no deployment of any high-energy weapons." -- page 5

"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." -- page 5

"To-date, every laser which has been scaled to MW-class average power falls in the chemical category." -- page 10

"Militarized devices at the 50 kW to 100 kW should be available within the next 15 years and it's not difficult to imagine MW systems within 20 to 30 years." -- page 15

"There is a popular misconception that there are "eye safe" laser wavelengths in the infrared. The reality is that any wavelength in the UV, visible or infrared can damage the eye or skin." -- page 26

"If the pressure-vessel portion of the spacecraft were penetrated, even in a small area, it could prove fatal." -- page 28

"The storage and removal of heat from any of these electrically powered lasers may prove to be a more stressing task than generation of the required prime power for lasing." -- page 29