Ionization rates and harmonic generation for H interacting with laser pulses of and peak intensities in the range -

Abstract

We applied the state-specific expansion approach (SSEA) to the solution of the time-dependent Schrödinger equation describing the interaction of H with laser pulses of λ = 1064 nm and peak intensities I0 = 2 x 1013, 6 x 1013, 1 x 1014 and 2 x 1014 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 I0 = 1 x 1014 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 I0 = 2 x 1014 W cm-2, the most difficult case treated thus far. This spectrum shows a cut-off at the 65th harmonic (3.17 Up + Ip) and an extended plateau containing low-intensity harmonics up to the 181st. The ionization rate is 1.7 x 1013 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.