Odd-even harmonic emission from asymmetric molecules: Identifying the mechanism

We study odd-even high-order harmonic generation (HHG) from oriented asymmetric molecules HeH²⁺ numerically and analytically. The variational method is used to improve the analytical description of the ground-state wave function for the asymmetric system, with which the ground-state-continuum-state transition dipole is evaluated. The comparison between the odd-even HHG spectra and the improved dipoles allows us to identify and clarify the complex generation mechanism of odd-even harmonics from asymmetric molecules, providing deep insights into the relation between the odd-even HHG and the asymmetric molecular orbital.