Seminar by Assoc. Prof. Dr. Phan Thi Ngoc Loan and MSc. Nguyen Thi Hien

On September 19, 2024, the lectures from Assoc. Prof. Dr.  Phan Thi Ngoc Loan, MSc. Nguyen Thi Hien  takes place in the meeting Room C

Assoc. Prof. Dr. Phan Thi Ngoc Loan presents about "Multielectron effects in high harmonic generation: from frequency shift to odd-even intensity modulation"

Abstract:

Fully comprehending the manifestations of multielectron effects in high-order harmonic generation (HHG) is essential to studying and extracting information about the core electrons. A prominent manifestation of the multielectron effect is the multielectron polarization (MEP) of the core electrons. Recently published studies have demonstrated the MEP effects on the intensity of the HHG spectra and, more specifically, the even-to-odd ratio, i.e., the ratio between the intensities of the even and adjacent odd harmonics. However, besides the HHG intensity, another important aspect of HHG spectra is the harmonic frequency. The question is whether the MEP affects this feature and whether there is any relation between the MEP effects on the even-to-odd ratio and on the harmonic frequency.

MSc. Nguyen Thi Hien presents about " Imprints of multielectron polarization effects in odd-even harmonic generation from CO molecules"

Abstract: 

Dynamic core-electron polarization (DCeP) is a correction to the single-active electron (SAE) approximation by considering a response of the core electrons to the time-dependent laser field. Despite being initially construed as a perturbative correction, in some cases especially atoms and molecules with large polarizabilities, DCeP can qualitatively alter predictions produced by the bare SAE theory. In this study, we unambiguously demonstrate the nonperturbative role of DCeP in the resolved odd-even high-order harmonic generation (HHG) of the CO molecule. In particular, we find that the even-to-odd ratio, i.e., the ratio between the harmonic intensities of even order and average of the two adjacent odd orders, changes by as much as one order of magnitude when DCeP is included, making the theoretically predicted values remarkably consistent with the experimental ones. This strong manifestation allows us to verify the DCeP role in HHG by experimental data. Furthermore, our analysis of the harmonic time profile shows that this agreement is not an artifact of the numerical method but reflects relevant physics, establishing that DCeP must be incorporated into the standard framework for strong-field physics.