Sub-Doppler extra-lines in the vicinity of the 388 nm line of Cs: A signature for dimer photoassociation in a thermal vapour ?

The paper reports on the observation of extra sub-Doppler resonance in the vicinity of the third resonance line of Cs (6Srarr8P) at 388 nm (6S_1/2rarr8P_3/2) and 389 nm (6S_1/2rarr8P_1/2), when saturated absorption spectroscopy is usually expected to provide a frequency reference in the analysis of other physical processes. All the extra-lines that were detected were located inside the Doppler width, with supplementary components appearing when increasing the irradiating intensities. These observations help to rule out the possibility to explain these observations by a resonant nonlinear optical process, as may occur in the presence of nonlinear processes involving two resonant beams, and mixing- up resonant absorption (or gain) with dispersion. A noticeable difference with photo-association performed with cold atoms is that here, in spite of a velocity-selection induced by saturated absorption, this process is only operated along a single velocity-axis, so that the interaction time between the two atoms that associate is expected to remain extremely short.