Einstein coefficients, cross sections, f values, dipole moments, and all that

TL;DR

This paper reviews the relationships among key parameters describing optical transition strengths in atoms and molecules, emphasizing their application to light-matter interactions and highlighting common pitfalls in their interpretation.

Contribution

It provides a comprehensive review and clarification of the relationships among Einstein coefficients, cross sections, f values, and dipole moments, correcting misconceptions from earlier literature.

Findings

Clarified relationships among optical transition parameters

Highlighted common pitfalls in parameter interpretation

Updated foundational understanding of light-atom/molecule interactions

Abstract

The relationships among various parameters describing the strength of optical transitions in atoms and molecules are reviewed. The application of these parameters to the description of the interaction between nearly monochromatic, directional light beams and atoms and molecules is given careful attention. Common pitfalls in relating these parameters are pointed out. This is a revised (February, 2002) version of a paper that originally appeared in Am. J. Phys. 50, 982-986 (1982).