No abstract

The interference fringes of above-threshold ionization (ATI) spectrum from atoms or molecules have been extensively studied. In this paper, we investigate the ATI of the polyatomic molecule SF6 in IR + XUV two-color laser fields, and find that some interference fringes on the spectrum are from the molecular structure, which is independent of the parameters of the laser field. Based on the frequency-domain theory, we analyze the interference fringes for different orbitals of SF6 molecules in detail. It is found that the orbital of SF6 can be simplified by several terms in the region of high value of momentum, where the destructive interference fringes from these terms may carry the information of the molecular structure. Furthermore, we obtain destructive interference formulas from these simplified orbitals, which may predict the interference fringes on the ATI spectrum. Additionally, we may obtain the information about the bond length of molecules. It will be useful for the study of the ionization spectrum of polyatomic molecules.

The direct above-threshold ionization (ATI) of diatomic molecules in linearly-polarized infrared and extreme ultraviolet (IR+XUV) laser fields is investigated by the frequency-domain theory based on the nonperturbative quantum electrodynamics. The destructive interference fringes on the angle-resolved ATI spectra, which are closely related to the molecular structure, can be well fitted by a simple predictive formula for any alignment of the molecular axis. By comparing the direct ATI spectra for monochromatic and two-color laser fields, we found that the XUV laser field can both raise the ionization probability and the kinetic energy of the ionized electron, while the IR laser field can broaden the energy distribution of the ionized electron. Our results demonstrate that, by using IR+XUV two-color laser fields, the angle-resolved spectra of the direct ATI can image the structural information of molecules without considering the recollision process of the ionized electron.