Direct Observation of Atomic Energy Level Shifts in Two-Photon Absorption

Abstract

We report direct observation of optically induced shifts of atomic energy levels in sodium vapor that occur in two-photon absorption. These shifts must be considered in high-resolution two-photon spectroscopy. Two cw dye laser beams of different frequencies and propagating in opposite directions are utilized to obtain high-resolution spectra. The intensity and frequency dependence of the level shifts are examined.