Fourier transform spectroscopy
![An example of a spectrum: The spectrum of light emitted by the blue flame of a butane torch. The horizontal axis is the wavelength of light, and the vertical axis represents how much light is emitted by the torch at that wavelength.](/Images/godic/202501/14/Spectrum_of_blue_flame.svg0243.png")
![An](/Images/godic/202501/14/FTIR-interferogram.svg0243.png")
![The Fourier transform spectrometer is just a Michelson interferometer but one of the two fully reflecting mirrors is movable, allowing a variable delay (in the travel-time of the light) to be included in one of the beams.](/Images/godic/202501/14/Fourier_transform_spectrometer0243.png")
Fourier transform spectroscopy is a measurement technique whereby spectra are collected based on measurements of the coherence of a radiative source, using time-domain or space-domain measurements of the electromagnetic radiation or other type of radiation. It can be applied to a variety of types of spectroscopy including optical spectroscopy, infrared spectroscopy (FTIR, FT-NIRS), nuclear magnetic resonance (NMR) and magnetic resonance spectroscopic imaging (MRSI), mass spectrometry and electron spin resonance spectroscopy. There are several methods for measuring the temporal coherence of the light (see: field-autocorrelation), including the continuous wave Michelson or Fourier transform spectrometer and the pulsed Fourier transform spectrograph (which is more sensitive and has a much shorter sampling time than conventional spectroscopic techniques, but is only applicable in a laboratory environment).