Role of Rotational Wave Packets in Strong Field Experiments

Complex revival features of rotational wave packets are obtained from the interplay of a molecular rotational distribution and a measured physical observable. The analysis of the measured temporal behavior can be used to retrieve either one or both quantities. We show here the first observation of high order fractional revival (up to $1/12$ in ${\mathrm{CO}}_2$) using time-of-flight measurements of ion yields leading to the information required for full reconstruction of the rotational wave packet. We further show via an analysis of higher order fractional revivals in high harmonic generation that new information on the participating ionic channels can be clearly identified, showing the general implication of our results.

Figure 1

(Top) Temporal evolution of the $⟨{\cos }^2\theta ⟩$ observable of a molecular rotational wave packet in units of rotational period. The corresponding probability density of alignment is illustrated at specific times. (Bottom) Angular shape of the rotational probability density including the Jacobian $\sin \theta$ plotted in black (dashed line) at the specific times depicted by letters on top. The red solid line is a retrieval of the probability density from a simulated experiment (see text) obtained from a sample of angles shown by black crosses.

Figure 2

Pump-probe scheme for measuring the rotational distribution of impulsively aligned ${\mathrm{CO}}_2$ molecules. See text for details. Inset: Typical measured time-of-flight spectrum.

Figure 3

Left: Measured fragment yields as a function of pump (alignment) and probe (Coulomb explosion) delay in red. Black dashed lines: Simulated behavior using Eq. (4) and extracted collection angle (see Table 1). Right: Zoom over the blue rectangles. The vertical dashed blue line highlight the position of the $1/8$ revival while the dash-dotted magenta one shows the $1/12$.

Figure 4

Simulated high harmonic yield (31st harmonic of the 800 nm light) from the three first orbitals of aligned ${\mathrm{CO}}_2$ molecules as a function of pump probe delay. (Top) Evolution over a rotational period for $\alpha =0^{\circ }$. (Bottom) Zoom over the rectangle for $\alpha =0^{\circ }$, 20°, 40°, and 90°. The vertical green dashed line highlights the position of the $1/8$ revival.