Quantum theory of photon emission during strong-laser-field-induced ionization
D. B. Milošević
Abstract
We formulate a quantum theory of photon emission during strong-laser-field-induced ionization and show that such photons can be emitted in a single-step process. The probability of this process is many orders of magnitude higher than that of the well-known high-order harmonic generation, which is a three-step process. We analyzed photon emission for various wavelengths and intensities of the laser field and found that the probability of photon emission is maximal for energies near 5 eV and that it can be shifted to higher energies for higher intensity. For a bichromatic linearly polarized laser field the photon emission rate can be controlled with the relative phase between the field components and can be one order of magnitude higher than in the monochromatic case. For circular laser polarization the rate of photon emission is lower than for the linear one and it depends on the emitted photon direction (it is much lower if the emitted photon polarization is perpendicular to the laser-field polarization plane). For the counterrotating bicircular field the rate is much higher than for the corotating bicircular field, monochromatic circularly and linearly polarized fields, and bichromatic linearly polarized field. The rate is the highest for orthogonally polarized two-color field for the relative phase $\ensuremath{\pi}/2$.