Recently the effect of the relative phase φ in a high-intensity (∼1014 W/cm2) two-color (bichromatic) CW laser with frequencies ω and 2ω on the high-order harmonic generation (HHG) was studied within the framework of the non-Hermitian quantum mechanics (NHQM) [Phys Rev A 2004, 69, 043404/1]. Here we emphasize the study of symmetries in bichromatic HHG spectra within the framework of the conventional Hermitian QM, and in particular by taking the duration of the laser pulse into consideration (an effect that has not been included in the non-Hermitian studies due to the time asymmetry problem in NHQM). The phase dependence of HHG and intense-field ionization probability in a 1D Xe atom with symmetric field-free potential and symmetric initial wave function were studied numerically and analytically. From simulations based on a single-particle response it can be seen that the HHG spectra is symmetric with respect to inversion in the relative phase between the two colors φ only if ionization is forbidden in the system and the laser pulse is an adiabatic one. The HHG spectra is symmetric with respect to a π-shift in φ whenever the laser pulse is an adiabatic one, either for bound or open (ionized) systems. The ionization probability is symmetric both to inversion or π-shift in φ the component probabilities (right- and left-ionization probabilities) have the same φ-dependence, up to a shift of π.
- Atoms in bichromatic strong laser pulses
- High order harmonics
- Nonlinear phenomenon
- Photo-induced ionization