Complicated high-order harmonic generation due to the falling edge of a trapezoidal laser pulse

TL;DR

This paper investigates how the falling edge of trapezoidal laser pulses affects high-order harmonic generation in H$_2^+$, revealing redshifts and spectral complexities that depend on pulse duration and nuclear motion.

Contribution

It demonstrates that the falling edge of trapezoidal pulses causes spectral redshifts and complexities in HHG, which are distinguishable when considering pulse duration and nuclear dynamics.

Findings

Redshift and spectral complexity occur at the falling edge of trapezoidal pulses.

These effects can be mitigated by adjusting pulse duration and nuclear motion considerations.

Spectral features are linked to electronic and vibrational state interferences.

Abstract

High-order harmonic generation (HHG) is investigated for H$_2^+$ and its isotopomers under seven- and ten-cycle trapezoidal laser pulses at 800 nm wavelength and $I$=4$\times 10^{14}$ W$/$cm$^2$ intensity. We solved numerically full-dimensional electronic time-dependent Schr\"{o}dinger equation with and without the Born-Oppenheimer approximation. We show that the HHG at the falling edge of a trapezoidal laser pulse can result in redshift and complexity on the total HHG spectrum which can be removed by considering different laser pulse duration and nuclear motion not possible for sin$^2$ and Gaussian laser pulses. We resolve the redshifts and complexities of the HHG spectra into different electronic and vibrational states and their interferences.