The Michelson interferometer scheme used in Fourier transform infrared (FTIR) spectrometers is based on Fourier beam splitters and compensators. FTIR spectrometers are typically based on Michelson interferometers, where one mirror is movable. Two mirrors are located on the two arms of the interferometer and oriented perpendicular to each other. The beam splitter is placed at the vertex of a right angle and oriented at a 45 ° angle relative to each mirror. The light transmitted to the beam splitter is divided into two parts (ideally 50%/50%), which further propagate to the two arms and reflect off the mirror. The beam reflected once from the beam splitter (the upper beam in the figure) must also pass through there and return through a tilted compensation plate to compensate for the other beam actually passing through the beam splitter three times instead of once. Scan a movable mirror at a certain distance to generate an interference pattern of two beams reaching the detector.