High-harmonic generation and spherically confined hydrogen atom

Abstract

The dynamics of a hydrogen atom in a spherical box under the action of a strong infrared femtosecond laser is numerically investigated. The spherical box is introduced to model collisions of ionized electrons with neighboring atoms to model their influence on high-order harmonic generation. The physical situation appropriate for such application is considered in detail. The presence of tunneling in the process is investigated. In the strong field limit this consideration is extended including a dressing approach in the calculation. The harmonic spectrum is calculated for a small radius of the sphere assuming a high gas pressure. The intensities of the harmonic lines are reduced and the envelope of the spectrum is strongly modified with respect to the plateau of harmonics. The inclusion of the dressing approach in the calculation can significantly modify this result. The situation is changed if a kicking electric field is added at the moment when ionization probability has local maximum. The electron kinetic energy is drastically increased, and as a consequence of the dynamic Stark shifts in the kicking field, and an unusual electron recombination is possible. The odd harmonics of a very high-order and a somewhat different form of plateau of harmonics appear. The intensities of so obtained single-atom harmonic emission are dramatically enhanced. To check the reliability of the model with an impenetrable spherical box, high-pressure argon gas is also considered in relation to the single atom high-order harmonic generation.