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  Interferometry, the study of interference effects in optical systems, helped prove that light both behaves as a wave function and had a particle nature. The wave character implied that in-phase components of separate light rays would constructively interfere, or sum their intensities and become brighter, whereas out of phase components would destructively interfere or cancel their intensities and become duller.

Thomas Young performed an experiment in 1800 demonstrating the interference of light by passing sunlight through pinholes in an opaque material, and observing light and dark interference fringes on a screen. Young used this experiment to calculate the wavelength of light waves and subsequently discovered that interferometers can be used as very accurate measurement instruments. Indeed the metre standard length is defined as 1,650,763.73 wavelengths of light from the Krypton 86 isotope, the measurements being performed using an interferometer.

Applications of interferometry include x-ray crystallography, where diffraction or ‘bending’ of x-rays around atoms in a crystal produces an interference pattern which presents details of the material\'s structure. The invention of crystallography helped prove that crystals had a regular molecular structure. Holograms, first produced by Gabor in 1948, record and reproduce 3-dimensional images by application of interferometry techniques. AC

See also wave-particle duality of light.



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