Two-photon evanescent-wave spectroscopy of alkali-metal atoms

The two-photon spectrum of sodium atoms, excited by two counterpropagating evanescent waves, is investigated both experimentally and theoretically. Su b-Doppler linewidths an observed, which are quantitatively reproduced by a rigorous theoretical approach that takes into account optical pumping and t ransit time broadening due to the translational motion of the arriving and departing atoms through the evanescent-wave fields. The velocity distributi on of the atoms desorbing from the surface is found to obey a cosine law, w hich has a significant influence on the observed line shapes. [S1050-2947(9 9)09407-X].