Intensities of hyperfine components in saturation spectroscopy

A theory is presented for the intensities of hyperfine components in saturation spectroscopy. We use a diagrammatic approach to nonlinear processes to derive closed-form formulas for the intensities of recoil doublets and of Doppler-generated level crossings. We discuss the influence of the terms introduced by hyperfine coherences in saturation spectroscopy. We also demonstrate spectroscopic stability when the hyperfine splittings are negligible. A catalog of simple formulas is given in view of applications to current spectroscopy and is illustrated by recent examples, including Doppler-free polarization spectroscopy. The extension to other sub-Doppler techniques such as two-photon Doppler-free spectroscopy is outlined.