Controlling Vibrational Wave Packet Motion with Intense Modulated Laser Fields

Intense, nonresonant laser fields produce Stark shifts that strongly modify the potential energy surfaces of a molecule. A vibrational wave packet can be guided by this Stark shift if the laser field is appropriately modulated during the wave packet motion. We modulated a 70 fs laser pulse with a period on the time scale of the vibrational motion ($\sim 10\mathrm{f}\mathrm{s}$) by mixing the signal and idler of an optical parametric amplifier. We used ionization of ${\mathrm{H}}_2$ or ${\mathrm{D}}_2$ to launch a vibrational wave packet on the ground state of $\mathrm{H}_2{}^{+}$ or $\mathrm{D}_2{}^{+}$. If the laser intensity was high as the wave packet reached its outer turning point, the Stark shift allowed the molecule to dissociate through bond softening. On the other hand, if the field was small at this critical time, little dissociation was measured. By changing the modulation period, we achieved control of the dissociation yield with a contrast of $90\%$.