Xue-Fei Pan

Asymmetric spatial distribution in the high-order harmonic generation of a H2 + molecule controlled by the combination of a mid-infrared laser pulse and a terahertz field

The control of the spatial distribution in the high-order harmonic generation (HHG) of a H2 + molecule is theoretically investigated by the combination of a mid-infrared laser pulse and a terahertz (THz) field. We use a THz pulse to steer the electron motion, and the numerical results show that the cutoff of the harmonic from the recombination of the electron with the nucleus along the negative-z direction is enhanced and the case along the positive-z direction is suppressed when a THz field is added. The underlying physical mechanism is illustrated by the semi-classical three step model and the ionization probability. The time-frequency analysis further demonstrates the asymmetric spatial distribution in a HHG controlled by adding a THz field.

Carrier envelope phase effect on the spatial distribution of high-order harmonic generation in asymmetric molecule*

The spatial distribution in high-order harmonic generation（HHG） from the asymmetric diatomic molecule He H2+ is investigated by numerically solving the non-Born–Oppenheimer time-dependent Schr?dinger equation（TDSE）. The spatial distribution of the HHG spectra shows that there is little contribution in HHG around the geometric center of two nuclei（z = 1.17 a.u.） and the equilibrium internuclear position of the H nucleus（z = 3.11 a.u.）. We demonstrate the carrier envelope phase（CEP） effect on the spatial distribution of HHG in a few-cycle laser pulse. The HHG process is investigated by the time evolution of the electronic density distribution. The time–frequency analysis of HHG from two nuclei in HeH2+ is presented to further explain the underlying physical mechanism.The spatial distribution in high-order harmonic generation (HHG) from the asymmetric diatomic molecule HeH2+ is investigated by numerically solving the non-Born–Oppenheimer time-dependent Schrodinger equation (TDSE). The spatial distribution of the HHG spectra shows that there is little contribution in HHG around the geometric center of two nuclei (z = 1.17 a.u.) and the equilibrium internuclear position of the H nucleus (z = 3.11 a.u.). We demonstrate the carrier envelope phase (CEP) effect on the spatial distribution of HHG in a few-cycle laser pulse. The HHG process is investigated by the time evolution of the electronic density distribution. The time–frequency analysis of HHG from two nuclei in HeH2+ is presented to further explain the underlying physical mechanism.

Controlling the contributions to high-order harmonic generation from different nuclei of N2 with an orthogonally polarized two-color laser field*

The generation of high-order harmonic and the attosecond pulse of the N-2 molecule with an orthogonally polarized two-color laser field are investigated by the strong-field Lewenstein model. We show that the control of contributions to high-order harmonic generation (HHG) from different nuclei is realized by properly selecting the relative phase. When the relative phase is chosen to be phi= 0.4 pi, the contribution to HHG from one nucleus is much more than that from another. Interference between two nuclei can be suppressed greatly; a supercontinuum spectrum of HHG appears from 40 eV to 125 eV. The underlying physical mechanism is well explained by the time-frequency analysis and the semi-classical three-step model with a finite initial transverse velocity. By superposing several orders of harmonics, an isolated attosecond pulse with a duration of 80 as can be generated.

Spectral redshift of high-order harmonics by adding a weak pulse in the falling part of the trapezoidal laser pulse

We investigate the spectral redshift of high-order harmonics of the H2 + (D2 +) molecule by numerically solving the non-Born–Oppenheimer time-dependent Schrodinger equation (TDSE). The results show that the spectral redshift of high-order harmonics can be observed by adding a weak pulse in the falling part of the trapezoidal laser pulses. Comparing with the H2 + molecule, the shift of high-order harmonic generation (HHG) spectrum for the D2 + molecule is more obvious. We employ the spatial distribution in HHG and time-frequency analysis to illustrate the physical mechanism of the spectral redshift of high-order harmonics.

High-order harmonic generation of CO2 with different vibrational modes in an intense laser field*

We apply the strong-field Lewenstein model to demonstrate the high-order harmonic generation of CO2 with three vibrational modes (balance vibration, bending vibration, and stretching vibration) driven by an intense laser field. The results show that the intensity of harmonic spectra is sensitive to molecular vibrational modes, and the high harmonic efficiency with stretching vibrational mode is the strongest. The underlying physical mechanism of the harmonic emission can be well explained by the corresponding ionization yield and the time–frequency analysis. Finally, we demonstrate the attosecond pulse generation with different vibrational modes and an isolated attosecond pulse with a duration of about 112 as is generated.