Effect of nuclear motion on high-order harmonic generation of H$_2^+$ in intense ultrashort laser pulses

TL;DR

This study explores how nuclear motion influences high-order harmonic generation in H$_2^+$ and D$_2^+$ molecules under ultrashort laser pulses, revealing isotope-dependent differences in harmonic yields and emphasizing the importance of nuclear dynamics.

Contribution

It provides a detailed numerical analysis of nuclear motion effects on HHG in H$_2^+$ and D$_2^+$, highlighting the need to consider multiple factors for accurate interpretation.

Findings

D$_2^+$ generally produces higher harmonic intensities than H$_2^+$ at most orders.

H$_2^+$ can generate more intense harmonics at certain low orders.

Nuclear motion, ionization, and dimensionality are crucial for understanding isotopic effects.

Abstract

High-order harmonic generation is investigated for H$_2^+$ and D$_2^+$ with and without Born-Oppenheimer approximation by numerical solution of full dimensional electronic time-dependent Schr\"{o}dinger equation under 4-cycle intense laser pulses of 800 nm wavelength and $I$=4, 5, 7, 10 $\times 10^{14}$ W$/$cm$^2$ intensities. For most harmonic orders, the intensity obtained for D$_2^+$ is higher than that for H$_2^+$, and the yield difference increases as the harmonic order increases. Only at some low harmonic orders, H$_2^+$ generates more intense harmonics compared to D$_2^+$. The results show that nuclear motion, ionization probability and system dimensionality must be simultaneously taken into account to properly explain the isotopic effects on high-order harmonic generation and to justify experimental observations.