Quantum State Reconstruction of a Rotational Wave Packet Created by a Nonresonant Intense Femtosecond Laser Field

We have experimentally determined the amplitudes and phases of a rotational wave packet in an adiabatically cooled benzene molecule, created by a nonresonant intense femtosecond laser field. In this wave-packet reconstruction, the initial wave packet is further interfered by a replica of the first laser pulse, and the resultant modulation in population is observed in a state-resolved manner. Though several states with different nuclear-spin modifications are populated in the initial condition, a single wave packet created from one of them (with $J=0$) is specifically reconstructed. Phase shifts characteristic of stepwise Raman excitation beyond the perturbative regime are experimentally identified.

Figure 1

Population of the $J_K=0_0$ state $|B_{0,0}(\tau ){|}^2$ in benzene molecules after double-pulse excitation, plotted against the delay $\tau$ between the two pulses. The ${}^{r}R_0(0)$ transition is used for probing the population. The black dots represent the observed value, and the red (or gray) line is the results from a least-squares fitting. The population was normalized against the value observed without the pump pulses.

Figure 2

Final population $A_J^2$ and phase ${\delta }_J$. (a) Retrieved from the observed data and (b) calculated by solving TDSE. The initial state is $|0,0,0⟩$.

Figure 3

(a) laser intensity dependence of ${\delta }_{J+2}-{\delta }_J$ calculated for a rotational WP of benzene created from the $|0,0,0⟩$ initial state. The laser pulse duration is fixed to 70 fs. (b) Experimentally derived ${\delta }_{J+2}-{\delta }_J$ plotted against $J$, along with the corresponding calculated ones for $10\mathrm{TW}/{\mathrm{cm}}^2$. Error bars for the experimental values denote one standard of deviation in the least-squares fitting.