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A speckle pattern is an intensity pattern produced by the mutual interference of a set of wavefronts.〔Dainty C (Ed), Laser Speckle and Related Phenomena, 1984, Sprinter Verlag, ISBN 0-387-13169-8〕 This phenomenon has been investigated by scientists since the time of Newton, but speckles have come into prominence since the invention of the laser and have now found a variety of applications. Laser speckle imaging has been used a diagnostic technique in which the features of scattered coherent light are explored. At first considered noise, the image of the scatter pattern actually contains information on the microstructure and micro-movements of the surface of a given tissue. By employing statistical analysis of the temporal and spatial fluctuations in the light scattered by microstructure dynamics and heterogeneities, it is possible to extract information on the dynamics of the abdominal wall in rats, pulp vitality in teeth and cerebral blood flow or even o the structure of dental tissue. Speckle patterns typically occur in diffuse reflections of monochromatic light such as laser light. Such reflections may occur on materials such as paper, white paint, rough surfaces, or in media with a large number of scattering particles in space, such as airborne dust or in cloudy liquids. ==Explanation== The speckle effect is a result of the interference of many waves of the same frequency, having different phases and amplitudes, which add together to give a resultant wave whose amplitude, and therefore intensity, varies randomly. If each wave is modelled by a vector, then it can be seen that if a number of vectors with random angles are added together, the length of the resulting vector can be anything from zero to the sum of the individual vector lengths—a 2-dimensional random walk, sometimes known as a drunkard's walk. In the limit of many interfering waves the distribution of intensities (which go as the square of the vector's length) becomes exponential , where is the mean intensity.〔Goodman, J. W. (1976). Some fundamental properties of speckle. JOSA, 66(11), 1145-1150〕 When a surface is illuminated by a light wave, according to diffraction theory, each point on an illuminated surface acts as a source of secondary spherical waves. The light at any point in the scattered light field is made up of waves which have been scattered from each point on the illuminated surface. If the surface is rough enough to create path-length differences exceeding one wavelength, giving rise to phase changes greater than 2π, the amplitude, and hence the intensity, of the resultant light varies randomly. If light of low coherence (i.e., made up of many wavelengths) is used, a speckle pattern will not normally be observed, because the speckle patterns produced by individual wavelengths have different dimensions and will normally average one another out. However, speckle patterns can be observed in polychromatic light in some conditions.〔McKechnie, T.S. 1976. Image-plane speckle in partially coherent illumination. Optical and Quantum Electronics 8:61–67.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「speckle pattern」の詳細全文を読む スポンサード リンク
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