Construct · 3 fields · 3 citations
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In optics, speckle is the mottled, grainy pattern of bright and dark spots seen when coherent light, such as a laser beam, scatters off a rough surface, because the many scattered wavelets arrive with random relative phases and interfere. Goldfischer's 1965 Autocorrelation function and power spectral density of laser-produced speckle patterns gave the statistical description of this pattern, treating its grain size and intensity distribution as a random field. The referent is a random interference pattern carrying information about the surface and the illumination, measured by its contrast and correlation length, and the identical phenomenon reappears in starlight and in ultrasound.[1]
In astronomy, the turbulent atmosphere breaks a star's image into a shifting cloud of speckles, each a tiny interference blob the size the telescope could resolve were the air still, so the detail is present but scrambled. Gezari, Labeyrie, and Stachnik's 1972 Speckle interferometry showed that analysing many short exposures of this speckle pattern recovers diffraction-limited information about the source. It is the same construct as laser speckle, random interference of coherent waves, here arising in the optical system of atmosphere plus telescope and exploited to measure stars rather than eliminated.[2]
In medical ultrasound, speckle is the granular texture overlaying B-mode images, produced when coherent sound echoes from the many small scatterers within tissue interfere, so the mottling reflects the interference pattern rather than the true anatomy. Burckhardt's 1978 Speckle in ultrasound B-mode scans analysed its statistics and showed it behaves like the speckle of coherent optics, limiting the detectability of fine features. It is the same random-interference construct as laser and stellar speckle, realised in an acoustic imaging system and quantified by the same contrast and correlation measures.[3]
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