Clocking enhanced ionization of hydrogen molecules using molecular rotational wavepackets

Laser-induced rotational wavepackets of hydrogen molecules have been experimentally observed in real-time by using two sequential 25-fs laser pulses (pump-probe scheme) and a COLTRIMs spectrometer. By measuring the time-dependent yield of the above-threshold dissociation and the enhanced ionization of the molecule, we observed a few-femtosecond time delay in between the two dissociation pathways for both H₂ and D₂. The delay was understood and interpreted by a classical model that considers enhanced ionization and thus additional interaction within the laser pulse. We demonstrate the molecule rotational clock in hydrogen molecule is a straightforward method for timing ultrafast molecular dissociation dynamics.