Modulation of the amplitude of a beam of
electromagnetic radiation; by the movement of a moving mirror in a rapid scan Fourier-transform spectrometer or by a mechanical chopper in other spectrometers.
Source:
PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 738 (https://doi.org/10.1515/pac-2019-0203)