Characterizing multiphoton excitation using time-resolved X-ray scattering

Molecular iodine was photoexcited by a strong 800 nm laser, driving several channels of multiphoton excitation. The motion following photoexcitation was probed using time-resolved X-ray scattering, which produces a scattering map $S(Q,\tau )$. Temporal Fourier transform methods were employed to obtain a frequency-resolved X-ray scattering signal $\tilde{S}(Q,\omega )$. Taken together, $S(Q,\tau )$ and $\tilde{S}(Q,\omega )$ separate different modes of motion, so that mode-specific nuclear oscillatory positions, oscillation amplitudes, directions of motions, and times may be measured accurately. Molecular dissociations likewise have a distinct signature, which may be used to identify both velocities and dissociation time shifts, and also can reveal laser-induced couplings among the molecular potentials.