Programme

O.16 -- Oral, VCTP-47

Date: Thursday, 4 August 2022

Time: 16:00 - 16:25

A method for retrieving asymmetricity of polar molecule from high harmonic generation

Kim-Ngan H. Nguyen (1), Ngoc-Loan Phan (2), Cam-Tu Le (3), Van-Hoang Le (2)

(1) Institute of Fundamental and Applied Sciences, Duy Tan University, Ho Chi Minh City, Viet Nam (2) Ho Chi Minh City University of Education, Ho Chi Minh City, Vietnam (3) Ton Duc Thang University, Ho Chi Minh City, Vietnam

High-order harmonic generation (HHG) is a highly non-linear optical phenomenon that can be observed when material interacts with an ultrashort intense laser pulse. HHG contains structural and dynamical information of atoms and molecules. Therefore, HHG is a powerful tool to probe the structure of atoms and molecules; and microscopic dynamics of electron and nuclei. The HHG emission can be understood by the semiclassical three-step model [1]. Accordingly, after propagating in an external electric field, the tunneling electron recombines into the parent ion, leading to the generation of the attosecond bursts with half-cycle time-spacing. For symmetric laser-target systems, generated attosecond bursts are identical (except a $\pi$ change). Considering the asymmetry system, specifically polar molecule in a multicycle laser pulse, attosecond bursts from two opposite sides are distinguished, both amplitude and phase. Therefore, this microscopic information reflects the asymmetry of polar molecules and becomes attractive to be investigated. Especially, the phase difference between two adjacent attosecond bursts in a train has been extracted from experiments in 2012 [2], in which the phase difference is extracted from the experimental even-to-odd harmonic ratio and the calculated amplitude ratio of the two adjacent attosecond bursts. This ratio is computed from the ionization rate and amplitude of recombination dipole whose accuracy strongly depends on the approximated theory level. In this work, firstly, we prove that the amplitude ratio and phase difference are inherent properties of polar molecules. We have tested their stability when changing the laser’s parameter. We found that the intensity imbalance and the phase difference is almost unchanged with various laser’s parameter. Then, we propose a general method to probe the intensity imbalance and the phase difference between two consecutive attosecond bursts from measured HHG data only. In particular, from measured HHG intensity and phase, one can construct the time-frequency spectrogram and directly retrieve the amplitude ratio and phase difference between adjacent attosecond bursts. Using the “numerical experimental” HHG data, we also check the validation of the method. The results show that the method works with high accuracy. Using the “numerical experimental” HHG data, we also check the validation of the method. The results show that the method works with high accuracy. [1] M. Lewenstein, P. Balcou, M. Y. Ivanov, A. L’Huillier, and P. B. Corkum, Phys. Rev.A, vol. 49, 2117, 1994. [2] E. Frumker et al., Phys. Rev. Lett, vol. 109, 233904, 2012.

Presenter: Nguyen Huynh Kim Ngan