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What is an Inteferometer

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A Michelson Interferometer is a device used to measure the speed of light in precise optical measurements. It does this by splitting light into two or more beams that recombine and interfere with each other causing the interference fringes. The interferometer basically consists of a light source, a beamsplitter, and two (or more) mirrors to reflect the light.

The interference pattern for a Michelson interferometer is circular-- that is, it produces concentric circles of light and dark "fringes". When one mirror on the interferometer is moving, the path difference between the two split beams of light changes, and the interference pattern is seen

Interference is a phenomenon that occurs when two photons of light interact with each other in such a way that their waves sum to either increase or decrease their total amplitude. Complete constructive interference occurs when two electromagnetic waves are of the same frequency and in phase; destructive interference occurs when two electromagnetic waves of the same frequency have a phase difference of one-half wavelength. When complete destructive interference occurs, no light can be detected. Similarly, complete constructive interference results in intensity quadrupling (intensity is proportional to the square of amplitude). The following picture demonstrates these effects.

Originally, the inventors of the interferometer produced it to measure the speed of light so they could determine the existence of ether. Since then it has been important in measuring the wavelengths of light, using the wavelengths of light to measure very small distances (up to 0.5 microns), to measure extremely small times (up to 1x10-15 seconds), and to study optical media.

Albert A. Michelson (1852-1931)

The Michelson interferometer was invented by American Physicist Albert A. Michelson in 1887. Michelson was born in Strzelno (Poland) in 1852 and moved to American in 1855. When he was 17, he joined the United States Naval Academy in Anapolis, Maryland where he excelled in science subjects. Michelson later became a science instructor at the academy, but moved on to become a professor of physics at several universities. During the years of 1923-1927, he was president of the National Academy of Sciences. In 1907, he was the first American to be awarded the Physics Nobel Prize for his many efforts in optics.

Michelson began experimenting with the interferometer in April of 1887. He came up with a system of mirrors and semi-transparent mirrors (or beamsplitters) for merging separated beams of light, which are coming from the same source. The system was set up so that the beam of light was split in two, sending each split perpendicular to each other, and then merging back so they “interfered” with each other.
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