directed-energy-weapons

Although there are several different methods by which high-energy lasing can be accomplished, the generic componentsof a laser weapon are always the same. There must be a power source with adequate fuel; there must be achamber in which coherent light is generated; there must be optical mechanisms for forming and focusing a beam;there must be sensors for tracking intended targets and characterizing the space between the laser and the targets;there must be beam-control techniques for shaping the beam and directing it so it traverses the intervening spacewith maximum efficiency; and there must be some method of assessing whether the energy deposited on the targethas had the desired effect.Assuming a specific degree of pointing accuracy, the lethality of the laser against any class of targets will be determinedby power level, wavelength and optical dimensions. These factors are typically traded off in designing an integratedsystem. Shorter wavelength enables designers to use less power or smaller optical dimensions and still achievedesired lethality, although the effects of atmospheric turbulence are more pronounced at shorter wavelengths. Higherpower or larger optics enables the same effect to be achieved at longer wavelengths with less degradation from turbulence.However, there are limits on each of these parameters dictated by physical laws. For example, a laser operatingat any given wavelength in the atmosphere will have a “critical power level” that defines its maximum lethality; athigher power levels, beam degradation resulting from interaction with the atmosphere will actually diminish energydeposited on the target. High power output can also exceed the tolerances of optical systems, leading to system failure. 15Considerable progress has been made over the last 20 years in advancing every facet of laser-weapons technology.Power levels have been boosted for the first time to megawatt ranges, a necessary step since three megajoules of energy-- the equivalent of three megawatts of power per second -- are needed to kill moderately hard aerospace vehicles(one pound of high explosives generates four megajoules of force). Optical coatings have been devised that can protectsensitive mirrors from these higher power levels without reducing beam efficiency. Sensing and tracking mechanismshave seen huge improvement, due primarily to the application of new information technologies.One of the most important technological developments is adaptive optics, a method of adjusting laser beams to compensatefor distortions that reduce the energy deposited on targets. Several extraneous factors can interfere with beampropagation through the atmosphere, including scattering, thermal blooming (heat-induced spreading), and defocusingdue to turbulence. In addition, performance factors intrinsic to the laser device itself can diminish the energy of thebeam at its point of destination. Adaptive optics measures these sources of distortion and deforms the beam at itspoint of origin so that it achieves maximum lethality after encountering such influences. In other words, the beam isactually more lethal when it reaches the target than where it began, because it is distorted in an amount and manner atthe source equal and opposite to the various contaminating influences that will be encountered en route to the target.When operating in the atmosphere, as most laser weapons do, adaptive optics can make as great a contribution toultimate lethality as factors such as power output and optical dimensions. In applications requiring atmospheric propagation,further refinement of the beam through rejection of distorting influences may be the main avenue open forincreasing weapon efficiency.The biggest engineering challenge in fielding laser weapons with military utility no longer resides at the subsystemlevel -- power sources, beam control, pointing mechanisms, etc. -- but at the integration level. The skills required tocombine all of the components of a laser weapon in a functioning and reliable system are still in their infancy. 16However, it is a measure of how far high-energy laser technology has progressed since the advent of the Strategic8 Directed-Energy Weapons: Technology and Programs