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The Defense Intelligence Agency produced this reference document, dated 31 March 2010, under its Advanced Aerospace Weapon System Applications (AAWSA) Program. It reviews the state of the art and likely evolution of high-energy laser weapons, including chemical, solid-state, fiber and free-electron lasers, as well as beam control and the history of DoD laser research. It concludes that electrically powered lasers could make megawatt-class weapons practical and that spacecraft laser weapons are conceivable within 20 years. It also recommends ways to protect spacecraft from laser damage.
UNCLASSIFIED/ ,'1"1!11'- l!ll"l"ll!lllit lal!i! s••t~r Typically in a chemical laser, 10 to 20 percent of the energy released in the chemical reaction will result in lasing while the other 80 to 90 percent becomes heat. Fortunately in a flowing gas laser, the heat can be easily removed from the resonator region of the gain generator by the exhaust gas. It is this efficient heat removal mechanism which has allowed chemical lasers to be scaled to such high average powers. If a MW-class laser were required today or in the next few years, chemical lasers provide the only available options. Because they use large quantities of hazardous chemicals and need refueling, this type of laser is not a preferred choice by the military. The physics and scaling of chemical lasers such as DF, HF, and COIL are well understood and, in principal, they could be scaled to power levels significantly beyond the MW level. However, due to the maturity of these technologies, only marginal further efficiency improvements are likely. As a result, the quantity of chemicals which must be stored and consumed for a laser beyond ~ 10 MW would make the concept highly impractical for space-based applications and extremely cumbersome for ground based lasers. Additionally, the atmospheric degradation of a laser beam propagating from ground to space makes these wavelengths impractical at power levels beyond 10 MW. SOLID-STATE LASERS The earliest and perhaps the most diverse laser category is the solid-state laser which uses specific atoms or molecules as a lasing gain medium (called the dopant) uniformly suspended in transparent crystalline or ceramic glass (called the host). For example, the familiar Nd:YAG laser uses a few percent of neodymium (Nd) atoms as the dopant suspended in a crystalline mix of yttrium, aluminum, and garnet (YAG). Figure 5 shows some of the many combinations of solid-state laser dopants and hosts in use or being developed today. 0.4 I 0. 5 0.6 0.7 1.isible rRuby Rhoda mine Nd:YAG X2 0.0 0.9 iTi:Sapphire Alexandrite Wavelength (microns) 1.0 Nd: YAG Yh:YAG 1.1 1.2 I 1.3 1.4 1.5 1.6 1.7 1.0 1.9 2.0 Er: YAG Er:Yll:YAG I Hosts can include: Ruby= Al2 ol: :Cr Sapphire"' Al203 YAG = Yittrium, Aluminum, Garnate = Y3Al50 12 LuAG = Lutetium, Aluminum, Garnate = Lu3Al50 12 Yittira = Y20 3 Ho: Figure 5. Common Solid-State Lasers and Their Wavelengths A major advantage of solid-state lasers for mobile or portable applications is that they only require electricity to power them although cooling is also needed. For example, a 5 second run of a 15 percent efficient 100 kW laser would require less than one kilogram of gasoline or diesel fuel. No hazardous chemicals are needed and an 6 UNCLASSIFIED//F81it 8FFIIIAI!: 1!181! &••1::Y
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Report, from the dia collection. The PDF is mirrored here; the original link is above. 31 pages are in the text index: search them above, or from the library's search.