Control of electron transfer and high harmonic generation in the linear triatomic system at large internuclear distances with short intense laser fields

Abstract

We numerically investigate high order harmonic generation (HHG) in the one electron linear H+– molecular system at large internuclear distances R = α and πα/2, where α is the ponderomotive radius, using ultra-short (two-cycles) intense (I > 1014 W cm −2) 800 nm laser pulses linearly polarized along the internuclear axis. We obtain the HHG spectra by solving exactly, in the Born–Oppenheimer approximation, the 3D time-dependent Schrodinger equation (TDSE). At large internuclear distances R, HHG spectra are obtained with an energy cut-off larger than the atomic maximum of I p + 3.17U p, where U p is the ponderomotive energy and I p is the ionization potential. The extended cut-off is shown to be related to the nature of electron transfer, whose direction is shown to depend critically on the absolute carrier envelope phase (CEP) of the ultrashort pulse. Constructive and destructive interferences in the HHG spectrum of coherent superpositions of electronic states in the H+– system are interpreted in terms of multiple electron trajectories from a time series analysis. Efficiencies of HHG are considerably enhanced by refocusing of the ionized electron trajectories with the neighbouring ion thus probing perturbative response of non-ionized electrons to few cycle intense laser pulses on attosecond time scales.