Ji-Gen Chen

Complex dynamics of correlated electrons in molecular double ionization by an ultrashort intense laser pulse

With a semiclassical quasistatic model we achieve insight into the complex dynamics of two correlated electrons under the combined influence of a two-center Coulomb potential and an intense laser field. The model calculation is able to reproduce experimental data of nitrogen molecules for a wide range of laser intensities from the tunneling to the over-the-barrier regime, and predicts a significant alignment effect on the ratio of double over single ion yield. The classical trajectory analysis allows us to unveil subcycle molecular double ionization dynamics.

Probing dynamic interference in high-order harmonic generation from long-range molecular ion: Bohmian trajectory investigation

Using Bohmian trajectory (BT) method, we investigate the dynamic interference in high-order harmonic generation from diatomic molecular ions. It is demonstrated that the main characteristics of the molecular harmonic spectrum can be well reproduced by only two BTs which are located at the two ions. This happens because these two localized trajectories can receive and store the whole collision information coming from all of the other re-collision trajectories. Therefore, the amplitudes and frequencies of these two trajectories represent the intensity and frequency distribution of the harmonic generation. Moreover, the interference between these two trajectories shows a dip in the harmonic spectrum, which reveals the molecular structure information.

Accurate prediction of interference minima in linear molecular harmonic spectra by a modified two-center model*

We demonstrate that the interference minima in the linear molecular harmonic spectra can be accurately predicted by a modified two-center model. Based on systematically investigating the interference minima in the linear molecular harmonic spectra by the strong-field approximation (SFA), it is found that the locations of the harmonic minima are related not only to the nuclear distance between the two main atoms contributing to the harmonic generation, but also to the symmetry of the molecular orbital. Therefore, we modify the initial phase difference between the double wave sources in the two-center model, and predict the harmonic minimum positions consistent with those simulated by SFA.

Chirp-free isolated attosecond pulse generation from an atom irradiated by a fundamental terahertz pulse synchronizing an infrared laser pulse.

We theoretically study high-order harmonic generation (HHG) and attosecond pulses from an atom irradiated synchronically by a terahertz (THz) pulse and an infrared laser pulse. For the HHG spectrum from the THz pulse alone and the combined pulse, an apparent peak-valley structure appears the platform region. Specially, for the periodic structure generated by an atom under the action of the combined pulse is originated from the interference between the electrons ionized at different instants in the laser field, which undergo many recollision and return to the core at the same time. Therefore, continuum harmonics with few chirps from the interference enhancement region can be achieved, which result in a chirp-free isolated attosecond pulse.