Abstract

High-order harmonic generation (HHG) of a strong laser field can provide a coherent short pulse of an extreme-ultraviolet (XUV) region. By using such a short XUV pulse, one can perform a time-resolved spectroscopy of tracing the ultrafast dynamics at a highly excited state including ion states. The molecular hydrogen ion H₂⁺ is a suitable system to demonstrate experimentally to trace a temporal evolution of wavepacket [1-3]. In the previous reports, either the Coulomb explosion of H₂²⁺ or the dissociation through the first electronic excited state 2pσ_u of H₂⁺ had been selected to the probe scheme for observation of the vibrational wavepacket (VWP) evolution. When the H₂⁺ in the 1sσ_g sate will be excited to the second electronic excited state 2pσ_u, the photoexcitation energy of 10 eV or higher is required. In the present work, we investigated the VWP dynamics of H₂⁺ by the XUV pump and probe time-resolved spectroscopy using short HHG pulses. We observed the time-dependent internuclear distance of H₂⁺ in the 1sσ_g state by using the multicolor probe pulse, which is one of the unique features of HHG pulse.

© 2014 Japan Society of Applied Physics, Optical Society of America