Abstract

The understanding of high-order harmonic generation processes has improved tremendously in the last year, with the two-step semi-classical approximation developed by Corkum and by Kulander et al. [1]. In a high-intensity low-frequency regime, the generation of harmonics occurs through the following process : the electron first tunnels out the barrier of the atomic potential lowered by the intense field. It is then accelerated in the laser field. If its trajectory encounters the nucleus, harmonics can be emitted, following the electron’s recombination to the ground state. A quantum-mechanical theory which recovers and justifies these semi-classical ideas has been formulated by Lewenstein et al. [2]. In addition, this approach, which is analytical to a large extent, allows for a rather simple computation of the harmonic components of the dipole moment. Consequently, it can be easily used as an input to the integration of propagation equations [3], to simulate experimental conditions. In this contribution, we apply this theory to two different problems (1) the study of the spatial coherence (amplitude and phase) of the harmonics, (2) the dependence of the polarization and rotation angle of the harmonics on the ellipticity and intensity of the incident laser field. We compare with experimental results [4,5].

© 1994 Optical Society of America