Theoretical exploration of harmonic emission and attosecond pulse generation from H-2(+) in the presence of terahertz pulse

Harmonic generation spectra from H-2(+) molecule ion driven by the chirped pulse combined with a terahertz (THz) pulse have been theoretically investigated by numerically solving the non-Born-Oppenheimer time-dependent Schrodinger equation (NBO-TDSE). The results show that with the introduction of the chirp, the harmonic cutoff is extended, resulting in a smooth supercontinuum. Further, when the initial vibrational state is prepared as v = 3, and by properly adding a THz controlling pulse, the harmonic yield is enhanced by almost six orders of magnitude compared with the single chirped pulse case. Quantum analyses are shown to explain the harmonic extension and enhancement. Furthermore, through the investigation of the isotopic effect, we find that more intense harmonics are generated in the lighter nucleus. Finally, by properly superposing the harmonics, a series of intense 35 as XUV pulses can be obtained, which are almost six orders of magnitude improvement in comparison with the single chirped pulse case