Strong field ionization yields in linear and asymmetric top molecules (Vol. 43 No. 2)
Total ionization yield of field-free aligned OCS (blue triangles, <cos2θ2d> = 0.84) and adiabatically aligned OCS molecules (red squares, <cos2θ2d> = 0.90) as a function of the angle between the polarization axes of the alignment and probe pulses (dashed curves are included to guide the eye). The ionization yield is modeled using standard MO-ADK (solid magenta) and Stark-shift-modified MO-ADK (solid green). Both calculations assume <cos2θ2d> = 0.90.
Ionization is a ubiquitous process when atoms and molecules are exposed to strong laser fields from femtosecond (fs) laser pulses. For molecules the understanding of how the direction of the electric field from the laser, with respect to the molecular orientation, influences ionization represents a particularly important point. Here we present a joint experimental and theoretical study on the orientational dependence of ionization of carbonyl sulphide (OCS), benzonitrile and naphthalene molecules by an intense linearly polarized laser pulse. Experimentally this is achieved by fixing the spatial orientation, by laser-based methods, of the molecules prior to the ionization event. For naphthalene and benzonitrile, the orientational dependence of the ionization yield agrees well with the calculated results, in particular, we observe that ionization is maximized when the probe laser is polarized along the most polarizable molecular axis. For OCS maximum ionization yield occurs when the probe is perpendicular to the internuclear axis, which is at odds with the calculated results.
Our findings suggest that the orientational dependence of the total ionization yields in linearly polarized fields is not only determined by the ionization rate but re-scattering of the released electron on the parent ion, left behind, must also be accounted for. This possesses new challenges for future theoretical modeling.
Orientation-dependent ionization yields from strong-field ionization of fixed-in-space linear and asymmetric top molecules
J. L. Hansen, L. Holmegaard, J. H. Nielsen, H. Stapelfeldt, D. Dimitrovski and L. B. Madsen, J. Phys. B: At. Mol. Opt. Phys. 45, 015101 (2012)
[Abstract]
