Sub-pulselength time resolution of bond softening and Coulomb explosion using polarization control of laser-induced alignment

Two 50 fs laser pulses with orthogonal laser E-fields are superposed with a time delay of less than the pulse duration, producing a single peaked pulse with a continuously varying ratio between the horizontal and vertical laser E-fields, Since the ejection angle of H+ fragments in the multiphoton dissociative ionization of H-2 is dependent upon the laser polarization, this technique can be used to resolve events on a sub-pulse timescale. Using focused intensities of about 5 x 10(14) W cm(-2), the results show that Coulomb explosion of H-2 occurs primarily on the rising edge of the pulse. Bond-softening peaks, however, are associated with the falling edge, in agreement with the earlier notion that only then can enhanced ionization at the critical internuclear separation be avoided. The surprisingly small energy spread of the bond-softening peaks, as observed in a recent high-resolution study, can be explained in a consistent manner.