absorption index

symbol: $k$
synonym: imaginary refractive index
https://doi.org/10.1351/goldbook.08220
Imaginary part of the complex refractive index describing absorption of electromagnetic radiation.
Source:
PAC, 2021, 93, 647. (Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)) on page 650 [Terms] [Paper]