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Features of the van der Waals Interaction on the Cesium $6S_{1/2} \rightarrow 7P_{3/2}$ Transition in an Optical Nanocell

We report the first experimental study of the influence of a dielectric surface on the transmission spectrum of cesium atoms for the $6S_{1/2} \rightarrow 7P_{3/2}$ ($D_2$) transition in vapor cells with thicknesses in the range $50$-$250\,$nm. The measurements were performed using a homemade optical nanocell filled with atomic cesium and featuring a wedge-shaped gap between the inner surfaces of sapphire windows. For atom-surface distances below approximately $300$\,nm, a significant red shift of the atomic transition frequency is observed due to van der Waals (vdW) interactions with the dielectric surface. An additional red shift arises at high vapor pressures owing to Cs-Cs interactions, with a measured contribution of $15$\,MHz/Torr, which must be accounted for in order to correctly determine the vdW coefficient $C_3$. By recording transmission spectra of the nanocell at different thicknesses, we determine for the first time the vdW coefficient for the Cs $6S_{1/2} \rightarrow 7P_{3/2}$ transition, obtaining values in the range $C_3 \sim 2- 20$\,kHz\,$μ$m$^3$. These results are of interest for fundamental studies of atom-surface interactions and are also relevant for the development of miniature sensors based on atomic vapors, in particular compact frequency references exploiting atomic transitions in the blue spectral region.