Jacquinot stop

synonym: J-stop
https://doi.org/10.1351/goldbook.08628
Aperture in the optics of a Fourier-transform spectrometer, typically between the source and the interferometer, designed to be the limiting aperture when no other optical element such as the detector serves this purpose.
Source:
PAC, 2021, 93, 647. (Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)) on page 752 [Terms] [Paper]