High-harmonic generation and periodic level crossings: time profile and control

Faria, C. Figueira de Morisson; Rotter, I

High-harmonic generation and periodic level crossings: time profile and control

Authors

Description

We investigate high-harmonic generation in closed systems, using the two-level atom as a simplified model. By means of a windowed Fourier transform of the time-dependent dipole acceleration, we extract the main contributions to this process within a cycle of the driving field. We show that the patterns obtained can be understood by establishing a parallel between the two-level atom and the three-step model. In both models, high-harmonic generation is a consequence of a three-step process, which involves either the continuum and the ground state, or the adiabatic states of the two-level Hamiltonian. The knowledge of this physical mechanism allows us to manipulate the adiabatic states, and consequently the harmonic spectra, by means of a bichromatic driving field. Furthermore, using scaling laws, we establish sharp criteria for the invariance of the physical quantities involved. Consequently, our results can be extended to a broader parameter range, as for instance those characteristic of solid-state systems in strong fields.
17 pages revtex, 15 figures (ps and eps files); figs. 1, 4, 6, 7, 10, 12 and 14 have been compressed due to memory problems