Michelson interferometer
Contents |
Configuration
If these two paths differ by a whole number (including 0) of wavelengths, there is constructive interference and a strong signal at the detector. If they differ by a whole number and a half wavelengths (e.g., 0.5, 1.5, 2.5 ...) there is destructive interference and a weak signal. This might appear at first sight to violate conservation of energy. However energy is conserved, because there is a re-distribution of energy at the detector in which the energy at the destructive sites are re-distributed to the constructive sites. The effect of the interference is to alter the share of the reflected light which heads for the detector and the remainder which heads back in the direction of the source.
In the late 1800's, the interference pattern was obtained by using a gas discharge lamp, a filter, and a thin slot or pinhole. In one version of the Michelson-Morley experiment, the interferometer used starlight as the source of light. Starlight is temporally incoherent light, but since it is a point source of light it has spatial coherence and will produce an interference pattern.
Application
The most well known application of the Michelson Interferometer is the Michelson-Morley experiment that provided evidence for special relativity. However, this configuration can be used for an assortment of different applications.
The Michelson Interferometer has been used for the detection of gravitational waves, as a tunable narrow band filter, and as the core of Fourier transform spectroscopy. There are also some interesting applications as a "nulling" instrument that is used for detecting planets around nearby stars. For most purposes, however, the geometry of the Mach-Zehnder interferometer is more useful.
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Interferometers