Interferometry is a group of techniques in which waves are superimposed in order to extract information about the waves. It is an important investigation technique in the fields of astronomy, fiber options, engineering, metrology, oceanography, seismology, spectroscopy, and many more.
Interferometers are used in science and industry for the measurement of small displacements, refractive index changes and surface irregularities. In analytical science, interferometers are used in continuous wave Fourier transform spectroscopy to analyse light containing features of absorption or emission associated with a substance or mixture.
Interferometry uses the principle of superposition to combine waves in a way that will cause the result of the combination to have some meaningful property that is diagnostic of the original state of the waves. This works because when two waves of the same frequency combine, the resulting pattern is determined by the phase difference between the two waves. The waves are in phase will undergo constructive interference while waves that are out of phase will undergo destructive interference. Interferometers use light or other electromagnetic waves to achieve this.