Relation between the propagation directions,
\(k_{\rm{i}}\),
\(k_{\rm{s}}\), and the polarization directions,
\(p_{\rm{i}}\),
\(p_{\rm{s}}\), of the incident and scattered radiation, usually expressed in terms of laboratory-fixed or crystal-fixed Cartesian axes.
Note:
A common notation, due to Porto, is \(k_{\rm{i}}(p_{\rm{i}}\,p_{\rm{s}})k_{\rm{s}}\).
Source:
PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 763 (https://doi.org/10.1515/pac-2019-0203)