double-beam spectrometer

https://doi.org/10.1351/goldbook.08241
Spectrometer in which beams of electromagnetic radiation from the source reach the detector via two paths, one through the sample and the other through a reference.
Notes:
  1. The radiant power in each beam is measured at each wavenumber.
  2. The output of a double-beam spectrometer is termed a double-beam spectrum. The ordinate of a double-beam spectrum is related to the radiant power that reaches the detector in the sample beam divided by that in the reference beam. The spectrum has a flat baseline where the sample does not absorb.
  3. The reference is usually a material having the same composition as the sample but lacking the analyte.
Source:
PAC, 2021, 93, 647. (Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)) on page 656 [Terms] [Paper]