Erratum: “An undergraduate measurement of radiative broadening in atomic vapor” [Am. J. Phys. 80, 740 (2012)]

The assertion in our recent Apparatus and Demonstration Note¹ that “the six Doppler-free peaks observed in the saturated absorption spectrum (SAS) of ⁸⁵Rb have an identical linewidth” is incorrect. In a multi-level atom, such as ⁸⁵Rb, optical pumping effects cause additional population removal from excited states. This leads to saturation intensities significantly lower than those expected from two-level theory that assumes, as we did in Ref. 1, that the saturation intensity is 1.64 mW/cm² for all three transitions and their three crossover peaks. For each transition, except the $Fg=3↔Fe=4$ transition, the effective saturation intensity is lower than the two-level value. Equation (1) in Ref. 1 shows that lowering the effective saturation intensity broadens the linewidth. Evaluating these effective saturation intensities is beyond the scope of the original Note, although it is worth noting that the role of...