Measurement of the atom-surface van der Waals interaction by transmission spectroscopy in a wedged nanocell

We demonstrate a method for measuring atom-surface interactions using transmission spectroscopy of thermal vapors confined in a wedged nanocell. The wedged shape of the cell allows complementary measurements of both the bulk atomic vapor and atoms close to surfaces experiencing strong van der Waals atom-surface interaction. These are used to tightly constrain the dipole-dipole collisional parameters of a theoretical model for transmission spectra that accounts for atom-surface interactions, cavity effects, collisions with the surface of the cell, and atomic motion. We illustrate this method on a cesium vapor in a sapphire cell, demonstrating that even the weakest of the van der Waals atom-surface interaction coefficients - for ground-state alkali atom transitions - can be determined with a very good precision. This result paves the way towards a precise quantitative characterization of atom-surface interactions in a wide range of atom-based nanodevices.