Angle-resolved spectra of the direct above-threshold ionization of diatomic molecule in IR + XUV laser fields

Abstract

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.

The interference fringes of above-threshold ionization spectrum of SF6 molecules in an IR + XUV laser field

“…In addition, the ATI spectrum present multi-plateau structures, where the width of each plateau in the ATI spectrum decreases as the angle θ f increases. These spectral structures are determined by the energy conservation during the ionization process [39], where the cutoff of each plateau decreases with the angle increasing. More interestingly, we may find that the interference fringes emerge in the high energy region of these spectra, which are attributed to the interference fringes in the density distribution of the molecular orbital shown in figure 3.…”

“…In this work, we consider the ATI process of polyatomic molecules SF 6 in IR + XUV two-color laser fields. The frequency-domain representation of the method for ATI in two-color laser fields is given in [38,39]. Here this method is briefly summarized and applied to a SF 6 molecule system.…”

“…This theory consists of two basic assumptions: (1) the whole system including the laser field and the atoms or molecules can be regarded as an isolated system, which satisfies the law of energy conservation; (2) the laser field is treated as a quantized field. The method has been extended to deal with recollision processes [36][37][38][39][40], which includes HATI, HHG and NSDI (nonsequential double ionization). In particular, Fu et al [40] applied the frequency-domain theory to HHG.…”

Numerical simulations of strong-field processes in momentum space*

“…In addition, the kinetic energy of the photoelectron may be up to 10U p (U p is the ponderomotive energy.) after rescattering from the core [1,2,4,5]. For example, if the laser intensity I = 1 × 10 14 W/cm 2 , wavelength λ = 800 nm, the full width at half maximum (FWHM) of the pulse σ =30 fs.…”

“…after rescattering from the core. [1,2,4,5] For example, if the laser intensity I = 1 × 10 14 W/cm 2 , wavelength λ = 800 nm, the full width at half maximum (FWHM) of the pulse σ = 30 fs, the radial box in real space should be R max = 2617 a.u. to include the backscattering electrons.…”