Two-Photon Near-Resonance Light Scattering from an Atomic Level

We have studied the time-resolved spectra, the energy-resolved spectra, and the total intensity of light emission induced by near-resonance two-photon excitation to the $4{}_{}{}^2{}_{}{}^{}D_{\frac{3}{2}}^{}{}_{}{}^{}$ and $4{}_{}{}^2{}_{}{}^{}D_{\frac{5}{2}}^{}{}_{}{}^{}$ levels of Na over the detuning range $-7\mathrm{} {\mathrm{cm}}^{-1\mathrm{}}<~\Delta <~7 {\mathrm{cm}}^{-1\mathrm{}}$. The time-resolved spectra of Na perturbed by Ar exhibit a fast adiabatic component and a slow resonance-fluorescence component. The cross section for phase-shifting, $T_2$-type collisions in this atomic system is $\sigma =110\mathrm{}\pm 20$ ${\mathrm{\AA }}^2$.