We study pump–probe spectroscopy of Rb vapor. Absorption spectra are presented for a weak probe beam in a room temperature vapor subject to a strong counter propagating pump beam of identical frequency. The importance of hyperfine pumping in the formation of the sub-Doppler spectrum is explained. For typical experimental parameters we clarify why the standard designation of “saturated absorption” spectroscopy is a misnomer. In contrast to saturated absorption, the details of the transient solution are crucial and hyperfine pumping leads to a modification of the absorption for detunings of many tens of natural linewidths from resonance.
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Smith et al. (2004) studied this question.