Interferometry is a family of techniques in which waves, usually
electromagnetic, are superimposed in order to extract
information about the waves. Interferometry is an important
investigative technique in the fields of astronomy, fiber
optics, engineering metrology, optical metrology, oceanography,
seismology, spectroscopy (and its applications to chemistry),
quantum mechanics, nuclear and particle physics, plasma physics,
remote sensing, biomolecular interactions, surface profiling,
microfluidics, mechanical stress/strain measurement, and
velocimetry.:1–2 Interferometers are widely 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. An
astronomical interferometer consists of two or more separate
telescopes that combine their signals, off