Michelson interferometer
The first implementation of a/LCI used a Michelson interferometer, the same model used in the famous Michelson–Morley experiment. The Michelson interferometer splits one beam of light into two paths, one reference path and one sampling path, and recombines them again to produce a waveform resulting from interference. The difference between the reference beam and the sampling beam thus reveal the properties of the sample in the way it scatters light.