I.5 -- Invited, VCTP-45
Date: Tuesday, 13 October 2020>
Time: 14:00 - 14:30>
Effect of dynamic core-electron polarization on harmonic process of linear molecules
Cam-Tu Le (1,2)
(1) Atomic Molecular and Optical Physics Research Group, Advanced Institute of Materials Science, Ton Duc Thang University; (2) Faculty of Applied Sciences, Ton Duc Thang University
This talk gives a review of dynamic core-electron polarization (DCEP) effect on the harmonic process of linear molecules. High-order harmonic generation (HHG) which is one of nonlinear phenomena occurring when atoms/molecules subjected to intense ultrashort lasers  has become a powerful tool to probe and control molecular dynamics. In principle, the strong-field processes can be obtained from directly solving the time-dependent Schrodinger equation (TDSE). However, in practical, this method is usually handled by using some schemes such as single-active electron approximation to apply for more-than-two-electron systems. In this framework, we investigate the influence of the DCEP , which is induced by the driving laser, on the HHG stimulated from linear molecules, such as CO – polar molecule and CO 2 – nonpolar molecule. With the few-cycle pulses, the results show that DCEP plays an essential role for the polar molecule CO, it makes the results meet the agreement with experimental and other theoretical results. By investigating the time-dependent ionization rate, we explain completely the DCEP mechanism: it affects the harmonic intensity through the ionization at a specific instant, rather than throughout the whole pulse propagation as understood. Furthermore, based on the instantaneous ionization rate, one can predict the influence of DCEP on the harmonic intensity of polar molecules . Meanwhile, for nonpolar molecules such as CO 2 , the DCEP can affect the harmonic process through a different mechanism – suppressing the distortion of the laser field on the highest occupied molecular orbital (HOMO) during the recombination phase, thus partially recovering the HOMO symmetry . Consequently, this shifts and sharpens the minima in the HHG spectra, which arise from the two-center interference . Furthermore, the influence of DCEP can manifest in case of multicycle pulses in which the DCEP affects the ratio of even-to-odd harmonic intensity emitted from CO due to the degree of symmetry breaking of the molecule-laser system . References:  A. McPherson et al., J. Opt. Soc. Am. B 4, 595 (1987).  B. Zhang, J. Yuan, and Z. Zhao, Phys. Rev. Lett. 111, 163001 (2013).  C.-T. Le, V.-H. Hoang, L.-P. Tran, and V.-H. Le, Phys. Rev. A 97, 043405 (2018).  C.-T. Le, D.-D. Vu, C. Ngo, and V.-H. Le, Phys. Rev. A 100, 053418 (2019).  M. Lein, N. Hay, R. Velotta, J. P. Marangos, and P. L. Knight, Phys. Rev. Lett. 88, 183903 (2002).  N.-L. Phan, C.-T. Le, V.-H. Hoang, V.-H. Le, Phys. Chem. Chem. Phys. 21, 24177 (2019).
Presenter: Le Thi Cam Tu