Waveform Modulation of High-Order Harmonics Generated from an Atom Irradiated by a Laser Pulse and a Weak Orthogonal Electrostatic Field

The detailed characteristics of the harmonics emission of atoms driven via a linearly polarized laser field combined with an orthogonal, weaker electrostatic field were investigated by numerically solving the time-dependent Schrödinger equation. It was found that the direction of the laser polarization and the polarization of the attosecond light, which is synthesized from the harmonic, can be controlled by the amplitude of the electrostatic field. With the analysis of the spatial distribution of the time-dependent dipole moment and the time-dependent evolution of the electronic wave packet, the control mechanism for the harmonic characters was investigated. The generation of harmonics in the vertical direction of the laser electric field is caused by the breaking of the symmetry of the time wave packet distribution. With this mechanism, we obtained circularly polarized attosecond light.