Ionization rates and harmonic generation for H interacting with laser pulses of lambda=1064 nm and peak intensities in the range 2x10(13)-2x10(14)W cm(-2)

We applied the state-specific expansion approach (SSEA) to the solution of the time-dependent Schrodinger equation describing the interaction of H with laser pulses of lambda = 1064 nm and peak intensities I-0 = 2 x 10(13), 6 x 10(13), 1 x 10(14) and 2 x 10(14) W cm(-2), and computed ionization rates and high-order harmonic spectra. For the first three cases, our results are compared with those of Krause and co-workers (Krause J L, Schafer K J and Kulander K C 1992 Phys. Rev. A 45 4998) who employed the grid method. Whereas for I-0 = 1 x 10(14) W cm(-2) convergence difficulties were reported for the grid method, no such difficulties were found for the SSEA. Given this fact, we tackled the problem of computing the harmonic spectrum for I-0 = 2 x 10(14) W cm(-2), the most difficult case treated thus far. This spectrum shows a cut-off at the 65th harmonic (3.17 U-p + I-p) and an extended plateau containing low-intensity harmonics up to the 181st. The ionization rate is 1.7 x 10(13) s(-1) while at the end of the pulse 19.5% of the system is in the 1s ground state and 2.6% in the bound states up to n = 20, l = 19.