Molecular hydrogen ion (H${{}_2}^{+}$) dissociation paths of bond softening (BS) and above threshold dissociation (ATD) are investigated exploiting few-cycle chirped laser pulses. 7-fs laser pulses are temporally broadened in a controlled way by the imposed positive chirp covering the range 7–55 fs. The dissociation of the H${{}_2}^{+}$ molecules via the BS and ATD paths is then systematically monitored as a function of the pulses duration in conditions of equal H${{}_2}^{+}$ yield. The experimental data show distinctive characteristics both in the energy dissociation spectral structure as well as in the yield as the pulse duration broadens. The interpretation of our experimental findings is supported by ab initio calculations based on the H${{}_2}^{+}$ dissociation time-dependent Schrödinger equation (TDSE) in a strong laser field, thus shedding light into the details of the underlying dissociation dynamics involving few-cycle pulses. The results are also analyzed within the Floquet picture discussing certain limits of its applicability. Finally, our experimental findings show strong molecular alignment for durations longer than 20 fs.

• Received 14 July 2012

DOI:https://doi.org/10.1103/PhysRevA.86.043428