Abstract
This paper develops an optical method to probe ultrafast electron correlations, based on bielliptical high harmonic generation. The authors use ab-initio numerical results to show that, with this approach, correlations are imprinted on the harmonic emission spectra, appear in a wide energy range, and persist far from any material resonant behavior.
Highlights
Many-body interactions play a significant role in the behavior of many atomic, molecular, and solid systems
Local density approximation (LDA) and Perdew-Burke-Ernzerhof (PBE) XC functionals lead to very different high harmonic generation (HHG) spectra from aligned CO, suggesting that there might be a breakdown of the local density approximation (LDA) in strongly driven CO
This result conceptually proves that extensions to multidimensional spectroscopy might enhance sensitivity to probing correlations. (ii) In Appendix 7 we find that for aligned CO, the ellipticity response of bielliptical HHG is as useful for probing correlations as the intensity-based response, which can be further utilized for ultrafast spectroscopy
Summary
Many-body interactions play a significant role in the behavior of many atomic, molecular, and solid systems. We find that the structure of the spectrograms is sensitive to the level of theory used in calculations, and even though corrections due to e-e interactions are generally small, they are qualitative and systematic, i.e., causing generic effects such as shifting of spectrogram peaks and changing their relative intensities These spectral signatures arise over wide energy ranges and in systems far from exhibiting multielectronic resonances. We demonstrate this phenomenon by performing ab initio calculations on several atomic (Ar, Kr, Xe) and molecular (carbon monoxide, CO) systems with varying levels of theory, showing that the spectrogram structure changes with different choices of exchange-correlation (XC) functionals in time-dependent density functional theory (TDDFT), and with the inclusion/exclusion of dynamical e-e interactions. The source of this sensitivity is investigated and found to be electrostatic e-e repulsion in atoms, while in molecules it arises from laser excitations of ultrafast correlations
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