Interference in two-channel two-photon ionization

Dana Z. Anderson, N. B. Baranova, Chris H. Greene +1 more

Min Liu, Yingchun Guo, Bingbing Wang

Using the frequency-domain theory, we investigate the above-threshold ionization (ATI) process of an atom in two-color laser fields. When both photon energies of the two-color laser fields are much smaller than the atomic ionization threshold, the ATI spectrum depends on the angle between the two lasers' polarization directions. While when the photon energy of one laser is comparable with or larger than the atomic ionization threshold, the ATI spectrum is independent of the angle, and only several dips appear at certain angles. By analyzing the contributions of different quantum channels, we find that, for the case that both frequencies of the two color lasers are low, the quantum interferences between the channels are strong, and hence the spectrum changes with the angle between the two lasers' polarization directions. While for the case that the frequency of one of the two color lasers is high, the contributions of the channels to the ATI spectrum decrease dramatically with increasing channel order, hence the interferences between the channels disappear, and the ATI spectrum has a step-like structure, which is independent of the angle between the two lasers' polarizations. These results can shed light on the study of the corresponding relation between classical and quantum mechanisms of the matter–laser interaction in high-frequency laser fields.

Andreas Becker, Jing Su, Hongcheng Ni +1 more

P. L. Knight

Yongfang Li

The phenomenon of ionization interference is studied with partial-wave expansion method through the particle population of the ionized state.Considering the interaction between splitted levels in the fine structure,the result of numerical simulation of the population in the state of ionization is given by n π pulses(n is integer or half-integer),and using proper approximate treatment,the analytic expressions of the particle population affected by the coherence in the ionized state is obtained.The results show that in the process of two-channel ionization,there is not only coherence between two waves,but also the modulation of coupling toward ionization.

Natalia E. Karapanagioti, D. Xenakis, Dimitrios Charalambidis +1 more

We report the observation of coherent control of the ionization rate in four-photon resonant, five-photon ionization schemes in Kr and Xe. The intermediate resonance is excited via different interfering channels involving four-photon absorption of the fundamental laser frequency ( ionization) as well as one third harmonic and one fundamental frequency photon absorption ( excitation), a particular aspect of the scheme being that interference occurs at a virtual level. By varying the relative phase of the two electromagnetic fields, a large modulation depth has been observed which is due to the chosen non-linear excitation scheme. In the Xe excitation experiment the interference between the different channels could be additionally probed through the modulation of the third-harmonic signal.