Abstract
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.
Highlights
Intense ultrafast-laser irradiation of molecules leads to nonlinear processes that can include multiphoton absorption, impulsive stimulated Raman scattering [1,2], and hyper-Raman fluorescence [3,4]
We show that the relative phase for different values of Q has physical meaning [14]
The strongest high-frequency feature in Fig. 7 is the bright narrow horizontal line at ω ≈ Æ40 × 1012 rad=s. (The data at angular frequencies below 5 × 1012 rad=s correspond to rotational wave packets that evolve over picoseconds and do not concern us here.) This line is associated with impulsive stimulated Raman scattering (ISRS) redistribution among the nearlyevenly-spaced vibrational levels of the ground state of the iodine molecule
Summary
Intense ultrafast-laser irradiation of molecules leads to nonlinear processes that can include multiphoton absorption, impulsive stimulated Raman scattering [1,2], and hyper-Raman fluorescence [3,4]. One prominent nonlinear process excited under these conditions is impulsive stimulated Raman scattering (ISRS) [2], a coherent two-photon redistribution of the initial population of the molecule into an oscillating vibrational wave packet in the ground electronic state [Fig. 1(a)]. This ground-state motion can be tracked through changes to the x-ray scattering pattern [11]. A table at the conclusion of the paper summarizes each nonlinear phenomenon, its measurement method, and when possible, comparisons to theory
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