Laser-induced collisional energy transfer: experimental study of the spectral profile

We report a measurement of the excitation spectrum of the laser-induced collisional energy transfer process for the Eu-Sr system in the weak-field regime. The measurement has been performed in a detuning range extending up to 85 cm-1 in the static wing, providing a wider check of existing theoretical models. The frequency resolution of the measurement (0.1 cm-1) was suitable for a quantitative study of the core of the line spectrum, where a comparison with the results of numerical calculations based on an effective three-level model gives complete evidence for a cooperative decay from the Sr(5p2)1D2 final level.