internal reflection element

https://doi.org/10.1351/goldbook.08624
Transparent or semi-transparent material of high refractive index that carries infrared radiation to a sample in internal reflection and attenuated total reflection measurements.
Note:
The sample is mounted in optical contact with the element.
Source:
PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 751 (https://doi.org/10.1515/pac-2019-0203)