optical spectroscopy

The study of systems by the electromagnetic radiation with which they interact or that they produce. By convention, spectroscopic properties are expressed in terms of @W06659@ in vacuo, not the @W06659@ within the medium being studied.
PAC, 1985, 57, 105. (Names, symbols, definitions and units of quantities in optical spectroscopy (Recommendations 1984)) on page 107 [Terms] [Paper]