Documents / Report
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.
UNCLASSIFIEDf }P81il 8PPIIItliL 'IS& tH•tY Advanced airframe structures, pressure vessels and radar domes are frequently fabricated using cut glass fibers or whole fiberglass cloth layers which are impregnated with epoxy resin. These materials typically fail through a combination of thermal ablation of the epoxy and delamination. Like metals, if the piece is under aerodynamic load or is part of a pressure vessel, failure will typically occur before complete burn- through although crack initiation and propagation is less likely due to the residual strength of the fiberglass cloth after the epoxy is removed. Also, like metals the energy required for penetration is thickness dependent. Ceramic materials, similar in composition to common Corning Ware, are routinely used in high temperature applications such as radomes for multi-mach air-to-air missiles or engine components. Although designed to handle heat when absorbed slowly, it will fracture and shatter if thermally shocked at moderate irradiance levels. Due to the poor thermal conductivity of ceramic materials, a thick piece of ceramic will shatter at almost the same irradiance and fluence levels as a much thinner piece. A discussion of laser-material interaction requires background information on the hazards of eye damage from laser radiation. 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. The damage mechanisms and damage thresholds, however, are a function of the laser's wavelength, pulse length and pulse energy (if pulsed) or average irradiance (if continuous). Laser wavelengths in the UV, visible and near infrared out to about 1.2 μmare the most dangerous. These wavelengths pass easily through the cornea and ocular fluid and are then focused on the retina where individual rods and cones can easily be permanently destroyed. This damage leaves the person with localized blind spots in the eye's field of view. Infrared wavelengths from about 1 μm to about 1.5 μm pass through the cornea but are absorbed by the eye's ocular fluid which results in localized heating. The damage threshold in this wavelength range is considerably higher than for retinal damage but in extreme cases the eye can be destroyed. Infrared radiation at wavelengths longer than about 1.5 ~tm is absorbed by the cornea and results in scarring similar to cataracts. Although it requires considerably more energy to damage the cornea than the retina, eye and skin safety at these wavelengths cannot be ignored. There are detailed ANSI standards which establish the Maximum Permissible Exposure (MPE) as a function of wavelength and pulse/continuous beam format. Figure 18 provides an example of single pulse MPE values for a variety of wavelengths. 21 UNCLASSIFIED/ /F81it 8FFI&I.«1k W&liii Ollk¥
Not linked to a story yet.
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.