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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//FIHl 8FFHil.t.ls. '11815 8HI£?/ extremely deep magazine becomes possible. These attributes combine to make solid- state lasers very attractive for both civilian and military applications. ROD AND SLAB LASERS The earliest solid-state laser mediums took the shape of a cylindrical rod and were optically pumped with flashlamps. Higher power solid-state lasers were later made using larger rectangular slabs since the amount of laser power which can be extracted increases with the lasing medium's volume. Additionally, rectangular geometries allowed more efficient optical pumping and cooling. Newer solid-state lasers were pumped with semiconductor diodes which emitted light more efficiently than flashlamps and at wavelengths which were more useable by the gain medium. Like chemical lasers, they are considerably less than 100 percent efficient overall and generate heat. However, solid-state lasers accumulate heat in the glass lasing medium where the resulting thermal stresses can distort the lasing beam enough to render it useless or even crack the glass. Since the glass-based medium is a poor thermal conductor, it is difficult to remove heat. Thus, thermal management of the gain medium imposes fundamental limits to increasing the average power in a single slab laser. Much of the recent research in slab lasers has focused on developing innovative ways to remove this heat or to combine beams from many smaller slabs. In order to combine laser beams in a fashion which retains good overall beam quality, the wavelength, phase, and polarization of the individual beams must be tightly controlled. This process is referred to as "coherent combination" or "phasing" and results in the maximum irradiance (watts/cm 2) by minimizing the focused spot area over which the total laser power is spread. If an application (such as welding or machining) depends more on total power than on minimizing spot size, then coherent combination is not needed and the laser beams can be separately focused to the same spot with no regard to differences in wavelength, phase, or polarization. This technique is called "incoherent combination." Major progress has been made in slab laser development during the last few years. Northrop-Grumman, under a DoD-funded program, recently produced 100 kW with good beam quality. This laboratory device, called the Joint High-Power Solid-State Laser (JHPSSL), uses a single Nd:YAG master-oscillator that feeds parallel, well-phased Nd:YAG power amplifiers. Brute-force power scaling, well beyond 100 kW, seems relatively straight-forward using approaches available today. Unfortunately, as more lasers are combined the overall beam quality will deteriorate while the parts-count, complexity, and fragility increases. This makes either militarization at the 100 kW level or laboratory scaling to/beyond the MW level unlikely in the near-term with this approach. However, given the recent rate of progress and the relative immaturity of the technology, it would be reasonable to expect further major technological breakthroughs in thermal management and phasing, cheaper/more powerful pump diodes (the major cost today), and far more rugged engineering. These improvements could be expected to yield affordable, rugged, militarily useful MW-class slab laser systems with reasonable beam quality within the next 20 years. Much of the relevant research is occurring outside of the United States. 7 UNCLASSIFIED//FIUl 8FFIIIAls. 1!1815 &••1tY
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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.