## Wikipedia - Indice di rifrazione refractive index, $$n$$

https://doi.org/10.1351/goldbook.R05240
The ratio of the speed of light in vacuum to that in a given medium.
Sources:
Green Book, 2nd ed., p. 30 [Terms] [Book]
PAC, 1996, 68, 957. (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 989 [Terms] [Paper]