Probing collision effects in the confined environment of a nanocell

The collisional effects in nanocell spectroscopy are investigated. Experiments performed on the well-resolved Cs D₁ line (894 nm), have enabled a simultaneous comparison of λ/2 and λ/4 thickness for various densities. Because nanocell spectroscopy, when performed under normal incidence irradiation, allows a sub-Doppler resolution owing to the velocity-selection operated by the transient regime of optical interaction, the pressure behaviour of the various hyperfine components can be studied individually. Considerable differences are found to occur for the pressure-induced shift, as already observed through selective reflection (SR) spectroscopy on the Cs D₂ line.