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Electronic speckle pattern interferometry
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<p>Electronic speckle pattern interferometry (ESPI), also known as TV holography, is a technique that uses laser light, together with video detection, recording and processing, to visualise static and dynamic displacements of components with optically rough surfaces. The visualisation is in the form of fringes on the image, where each fringe normally represents a displacement of half a wavelength of the light used (i.e. quarter of a micrometre or so). </p><p>ESPI can be used for <a href="/facts/Stress_(physics)/ErAXDbbd">stress</a> and <a href="/facts/Strain_(materials_science)/xK7R59oI">strain</a> measurement, <a href="/facts/Vibration_mode/XCsvQpuI">vibration mode</a> analysis and <a href="/facts/Nondestructive_testing/Czz0Vt0B">nondestructive testing</a>. ESPI is similar to <a href="/facts/Holographic_interferometry/ddq55HxY">holographic interferometry</a> in many ways, but there are also significant differences between the two techniques. </p>