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It is a device which splits a light beam into two parts and then recombines the parts to form an interference pattern. The device can be used to measure wavelengths or other lengths with great precision. The interferometer, invented by the American physicist A. A. Michelson (1852–1931).
The following figure shows schematic diagram of the interferometer in which a ray of light from a monochromatic source is split into two rays by mirror M, which is inclined at 45° to the incident light beam. Mirror M, called a beam splitter, transmits half the light incident on it and reflects the rest. One ray is reflected from M vertically upward toward mirror M1, and the second ray is transmitted horizontally through M toward mirror M2. Hence, the two rays travel separate paths L1 and L2. After reflecting from M1 and M2, the two rays eventually recombine at M to produce an interference pattern, which can be viewed through a telescope. The glass plate P, equal in thickness to mirror M, is placed in the path of the horizontal ray to ensure that the two returning rays travel the same thickness of glass.
The interference condition for the two rays is determined by their path length differences.
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Waves and Optics