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Seminar khoa học 21/2/2023

Vào 8:00 ngày 21 tháng 2 năm 2023, PGS.TS Phan Thị Ngọc Loan (Trường Đại học Sư phạm TP. Hồ Chí Minh) sẽ báo cáo về "Effects of Dynamic Core-Electron Polarization on High-Order Harmonic Generation from Multielectron Molecules".

Địa điểm: Phòng họp C


PGS Loan bắt đầu trình bày:

PGS. Loan bắt đầu trình bày

In the past few decades, the nonlinear laser-interaction has attracted unprecedented advances in both experimental and theoretical studies. The simplest model is popularly used, called single-active electron (SAE) approximation, where the core electrons are frozen but not the outermost electron. However, the SAE theory significantly deviates from the experimental observation for atoms and molecules with large polarizability; thus, its validation needs to be reconsidered.

The core-electron polarization is, in fact, large in a strong laser field, raising a question about the DCeP role. A recent study on the harmonic process has demonstrated the DCeP effect on the dynamic minimum of HHG from CO molecule [1]; however, a comprehensive investigation of the DCeP impact in different aspects of HHG is still desirable. 

Our recent studies show that the DCeP strongly affects different characteristics of HHG emitted from CO2 and CO molecules in a linearly polarized laser pulse. Firstly, we indicate that the DCeP can shift and sharpen the structural minima in the HHG from CO2 molecules [2]. Then, we demonstrate the significant DCeP effect on the intensity and shape of HHG from CO molecules at harmonics near the cutoff [3]. Finally, we find out that the DCeP dramatically modifies the even-to-odd ratio, i.e., the ratio between the intensities of the even and the average of the two adjacent odd orders [4,5]. The discrepancy between the two cases of including and neglecting DCeP is especially large, as much as one order. This strong effect of DCeP makes the simulated even-to-odd ratio nicely matches the available experimental data [6,7]. In Ref. [5], we also find out the DCeP impact on the harmonic phase besides the harmonic intensity found in previous studies [1,3,4].

It is natural to ask whether the DCeP effects on different aspects of HHG have the same origin. This report systematically discusses the physical underlying of DCeP imprints in HHG by considering each step of harmonic generation according to the three-step model. We show that the DCeP effect on HHG not only originates from the ionization and recombination steps but also from the propagation one. The propagation step influences the phase of harmonic bursts whose coherence dramatically impacts harmonic intensity. A further electron trajectories analysis is adopted to detect which step plays an essential role in the DCeP effect on harmonic generation. It is indicated that depending on the laser parameter, the weight of each step is differently contributed to the DCeP effect on HHG.


Buổi seminar bắt đầu

[1]    B. Zhang et al., Phys. Rev. A 90, 035402 (2014).
[2]    C.-T. Le et al., Phys. Rev. A 100, 053418 (2019).
[3]    C.-T. Le et al., Phys. Rev. A 97, 043405 (2018).
[4]    N.-L. Phan et al., Phys. Chem. Chem. Phys. 21, 24177 (2019).
[5]    H.T. Nguyen et al., Phys. Rev. A 105, 023106 (2022).
[6]    E. Frumker et al., Phys. Rev. Lett. 109, 233904 (2012).
[7]    P.M. Kraus et al., Phys. Rev. Lett. 113, 023001 (2014)