Attosecond pulse generation via multicolor beam superposition in the over-barrier ionization regime

Based on coherent superposition of multicolor continuous wave beams, high order harmonics and attosecond pulse generation from a hydrogen molecular ion (HMI), H-2(+), with different internuclear distances, R, are studied. Driving pulse intensity was taken to be 400 TW cm(-2), which can ionize an H-2(+) ion with R > R-b = 2.4 a.u. over the barrier. It is seen that cutoff harmonic with respect to R decreases until the over barrier ionization threshold, R-b, then becomes almost uniform to the end of R = 10 a.u. whereas it is almost constant with respect to the spectral width of the beams, Delta omega. Besides attosecond pulse intensity increases versus R, and decreases with respect to Delta omega so that the most intense attosecond pulses can be generated from HMIs with R >= 5 a.u. via the pulses by Delta omega <= 0.03 a.u. Attosecond pulse durations were insensitive to both Delta omega and R.