Programme

P.108 -- Posters, VCTP-50

Date: Thursday, 7 August 2025

Time: 08:30 - 10:00

Effects of laser parameters on orbital competition in high-order harmonic generation from hydrogen cyanide

Duong D. Hoang-Trong (1,2), Thanh Tran (3), Doan-An Trieu (4,5), Hien T. Nguyen (6), Van-Hoang Le (3), and Ngoc-Loan Phan (3)

(1) Simulation in Materials Science Research Group, Science and Technology Advanced Institute, Van Lang University, Ho Chi Minh City, Vietnam (2) Faculty of Applied Technology, School of Technology, Van Lang University, Ho Chi Minh City, Vietnam (3) Ho Chi Minh City University of Education, 280 An Duong Vuong Street, Ward 4, District 5, Ho Chi Minh City 72711, Vietnam (4) Institute of Fundamental and Applied Sciences, Duy Tan University, Ho Chi Minh City 700000, Vietnam (5) Faculty of Natural Sciences, Duy Tan University, Da Nang City 550000, Vietnam (6) Tay Nguyen University, Buon Ma Thuot City 63161, Vietna

Recent advances in laser technology have led to the discovery of various strong-field nonlinear phenomena, such as above-threshold ionization (ATI), high-energy ATI (HATI), nonsequential double ionization (NSDI), and high-order harmonic generation (HHG). These effects enable ultrafast imaging and tracking of electronic dynamics in atoms and molecules, necessitating accurate theoretical models to interpret the underlying mechanisms. A widely used and computationally feasible approach involves solving the time-dependent Schrödinger equation (TDSE) within the single active electron (SAE) approximation. Prior studies often attribute HHG signals predominantly to the highest occupied molecular orbital (HOMO), while neglecting the role of lower-lying orbitals. However, emerging evidence reveals the significance of multielectron effects, notably the contribution of HOMO-1 and its interaction with HOMO, which can manifest as observable changes in HHG spectra. In this work, we investigate the multiorbital contributions to HHG in hydrogen cyanide (HCN) molecules, focusing on the competition between HOMO and HOMO-1 under varying laser parameters. By numerically solving the TDSE using an SAE model that incorporates the orbital energies and permanent dipoles of both orbitals, we systematically examine how pulse duration, intensity, and wavelength affect their respective contributions. Our results show that the dominance of HOMO or HOMO-1 is not fixed but varies strongly with laser intensity and pulse duration, while remaining comparatively stable with respect to wavelength. Specifically, longer pulses and higher intensities enhance the role of HOMO-1, leading to suppression of HOMO contributions and shaping the overall HHG spectrum. Time-frequency analyses of the harmonics reveal that these dependencies originate from differences in the ionization probabilities and recombination dipole moments of the orbitals under changing field conditions. These findings underscore the importance of laser parameter selection when using HHG to probe multielectron dynamics and inner-valence orbital effects in asymmetric molecules.

Presenter: Hoàng Trọng Đại Dương