Alignment dependence of high harmonics contributed from HOMO and HOMO-1 orbitals of N₂molecules

Abstract

Characteristics of high harmonics generated from aligned N2 molecules were investigated by rotating the molecules with respect to the polarization of harmonic generation pulses. The high harmonics in the plateau and the cutoff regions showed distinctive behaviour, which could be explained from the calculation of transition dipole moments between recolliding electron and multi-orbitals of N2 molecule consisting of the highest occupied molecular orbital (HOMO) and the lower-lying orbital below HOMO (HOMO-1). It was also observed that the angular dependence of harmonics from aligned molecules with respect to the polarization of harmonic generation pulses was closely related to the geometrical structure of molecular orbitals, and that the harmonic in the transition region from the plateau to the cutoff was influenced comparably by both HOMO and HOMO-1. These results confirmed that high harmonic generation and molecular structure were closely linked.