Softening of the ${\mathrm{H}}_2^{+}$ molecular bond in intense laser fields

We report a new kind of multiphoton dissociation in intense laser fields. ${\mathrm{H}}_2^{+}$ molecular ions were formed in above-threshold ionization of ${\mathrm{H}}_2$ gas by intense 532-nm, 100-ps laser pulses. Observations suggest that multiphoton couplings soften the molecular bond, resulting in dissociation at laser intensities over 50 TW/${\mathrm{cm}}^2$. The ion-dissociation spectra have multiple peaks caused by multiphoton transitions during dissociation of ${\mathrm{H}}_2^{+}$.