Minimum structure of high-harmonic spectra from aligned O_(2) and N_(2) molecules

We experimentally investigated the high-order harmonic generation(HHG)from aligned O_(2) and N_(2) molecules in a linearly polarized laser field,and presented the dependence of the harmonic spectrum on the driving laser intensity and molecular alignment angle.The minimum position of HHG of O_(2) varies with changing the laser intensity,which is caused by multi-orbital interference.However,the location of the observed minimum structure in N_(2) harmonic spectrum remained unchanged upon changing the laser intensity.The mechanism of the spectral minimum for N_(2) case is regarded as a Cooperlike minimum in HHG associated with the molecular electronic structure.This work indicates that harmonic spectroscopy can effectively uncover information about molecular structure and electron dynamics.

S-matrix study on alignment dependence of single ionization of molecular ions with different active orbitals

The single ionization rate of the diatomic molecular ion H2^＋ with different active orbitals in an intense field is studied by using S-matrix theory. Our results show that the orientation-dependent single ionization probability of H2^＋ is greatly dependent on the symmetry and the electron density distribution of its initial states, and it can be used to identify the excited state of the molecular ion in the dissociation process.

Nonsequential double ionization of the aligned hydrogen molecule in strong field

This paper studies the nonsequential double ionization （NSDI） process of diatomic molecules aligned parallel and perpendicular to an intense linearly polarized laser field by using a three-dimensional semiclassical model. With this model, it achieves insight into the ion momentum distribution under the combined influence of a two-centre Coulomb potential and an intense laser field, and this result shows the significant influence of molecular alignment on the ratio between double and single ionization rate. Careful investigations show that the NSDI process for different alignment molecules has a close relation to the laser intensity and the different bounding electron distribution has a significant influence on the final ion momentum distribution.

High-order Harmonic Generation of Aligned Acetylene in Elliptically Polarized Strong Laser Fields

We perform an experimental study on high-order harmonic generation （HHG） of aligned acetylene molecules induced by a 35-fs 800-nm strong laser field, by using a home-built HHG spectrometer. It is observed that the molecular HHG probability declines with in- creasing the laser ellipticity, which is in consistence with the deduction fl＇om the well-known tunneling-plus-rescattering scenario. By introducing a weak felntosecond laser pulse to non- adiabatically align the molecules, we investigated the molecular orbital efl）ct on the HHG in both linearly and elliptically polarized driving laser fields. The results show that the harmonic intensity is maximum for the molecular axis aligned perpendicularly to the laser electric field. It indicates that both the highest occupied molecular orbitals （HOMO） and HOMO-1 contribute to the strong-field HHG of acetylene molecules. Our study should pave the way for understanding the interaction of molecules with ultrafast strong laser fields.