Orbital-resolved calculations of two-center interferences in linear triatomic molecules

Abstract

We perform ab initio calculations of high-harmonic spectroscopy (HHS) of two-center interference phenomena in oriented carbon dichalcogen molecules, using time-dependent density functional theory (TDDFT). We show that, by resolving the harmonic response into contributions from individual Kohn-Sham orbitals, we can extract target-specific characteristics for both the spectral amplitude and phase. We also discuss that this extraction is predicated on a careful analysis and normalization of the harmonic spectrum. Finally, we present field-free scattering calculations that mimic the recollision step in high-order harmonic generation and allow the calculation of recombination dipole matrix elements without explicitly calculating the scattering states of a molecule. We show that the orbital-resolved TDDFT HHS results and results based on our field-free scattering calculations are in very good agreement with each other.

Investigation of Interferences in Carbon Dioxide through Multidimensional Molecular-Frame High-Harmonic Spectroscopy

“…We select the HHG short trajectories, otherwise obtained in measurements through macroscopic effects, by using a complex absorbing potential at the edges of the box. Finally, we compute the HHS spectral amplitude and phase from the Fourier transform of the total or HOMO channel dipole signal, like in Hamer et al 36 We compare the results of the TDDFT HHS simulations with field-free scattering calculations, also presented in Hamer et al 36 The scattering simulations mimic the scattering step in the HHG process without explicitly calculating the scattering states of the molecule. This approach is based on releasing an electron moving within the DFT potential of the ground state, and then calculating the dipole signal from the ensuing dynamics.…”

Characterizing Particle-Like Charge Migration Dynamics with High-Harmonic Sideband Spectroscopy

“…In order to describe both the high-harmonic generation (HHG) and charge-migration (CM) processes, we use grid-based time-dependent density-functional theory (TDDFT) [25] with a local density approximation exchangecorrelation functional [26][27][28][29] and an average-density self-interaction correction [30] within Octopus [31,32]. Following the blueprint of [37], we put the BrC 4 H molecule at the center of the simulation box with the x axis parallel to the laser-polarization direction. We then vary molecular orientation by rotating the target inside that box.…”

“…For harmonic computations, we use a combination of A mid-infrared (MIR) field, with a peak intensity of 6 × 10 13 W/cm 2 , and a weak attosecond pulse train (APT) [36] consisting of the 9 th -to-17 th odd harmonics and having 2% of the MIR field amplitude. The timing of the APT, 0.08 optical cycles after the extrema of the MIR electric field, is set to enhance short trajectories [36,37]. Finally, we ramp up the MIR+APT field with a sin 2 envelope for two full optical cycles (followed by a constant-amplitude envelope), and control its delay ∆ with respect to the initiation of the CM dynamics.…”

“…We control both the laser frequency ω L and the delay between the MIR pulse and the initiation of the CM. To select the short-trajectory contribution that is usually observed in HHG measurements [34,35], we use a combination of a weak attosecond-pulse-train ionizationseed synchronized with the MIR [36] and a simulation box which is scaled to the quiver radius in the laser polarization direction [24,37]. Finally, we compute harmonic spectra from the total dipole acceleration in the direc-tion of the laser polarization.…”

“…Specifically, we perform a multi-cycle HHG-calculation as described above for several different delays spanning a half laser cycle. Then we collate the delay-dependent response from individual laser half-cycles [37] to obtain a time-resolved HHG yield that has both sub-cycle resolution and lasts long enough to resolve the CM-induced beating. In an experiment, this would correspond to using a short CEP-stabilized generation pulse with a controllable delay relative to the initiation of the CM, and scanning the delay with subcycle resolution over several laser cycles.…”