Speckles

Speckles are small, irregular spots of light and dark that appear in images formed with coherent light, such as laser light, when it is scattered by a rough surface or a turbid medium. They arise from the interference of many scattered wavefronts; slight changes in observation distance, wavelength, or surface structure can cause the pattern to shift or reorganize. The size of speckles is roughly on the order of the light's wavelength and depends on the imaging setup.

More broadly, speckle patterns are used as a tool in science and engineering. In laser speckle imaging and laser speckle contrast imaging, temporal fluctuations in the speckle pattern reflect motion within a scattering medium and can be used to map blood flow or tissue perfusion. In structural and material experiments, speckle patterns are tracked to measure displacement and strain through techniques such as speckle interferometry and digital image correlation. In ultrasound, speckle tracking analyzes tissue motion from the randomly scattered echoes.

In astronomy, speckle interferometry uses short exposure images of stars to overcome atmospheric blurring and reconstruct high-resolution information.

Speckle can also appear as unwanted noise in imaging, reducing contrast and resolution, but with appropriate processing and acquisition strategies it can be used as a source of quantitative information.