Uncovering multiple orbitals influence in high harmonic generation from aligned N$_2$

TL;DR

This paper demonstrates that the maximum in high harmonic generation from aligned N₂ molecules at the rotational half-revival is primarily due to the HOMO-1 orbital contribution, especially near the HHG cutoff, influenced by laser intensity.

Contribution

The study uses quantitative rescattering theory with accurate photoionization data to identify HOMO-1's role in HHG from N₂, clarifying the orbital contributions during the process.

Findings

Maximum at half-revival linked to HOMO-1 orbital.

HOMO-1 contribution increases near HHG cutoff.

HOMO-1 importance depends on laser intensity.

Abstract

Recent measurements on high-order harmonic generation (HHG) from N$_2$ aligned perpendicular to the driving laser polarization [B. K. McFarland {\it el al}, Science {\bf 322}, 1232 (2008)] have shown a maximum at the rotational half-revival. This has been interpreted as the signature of the HHG contribution from the molecular orbital just below the highest occupied molecular orbital (HOMO). By using the recently developed quantitative rescattering theory combined with accurate photoionization transition dipoles, we show that the maximum at the rotational half-revival is indeed associated with the HOMO-1 contribution. Our results also show that the HOMO-1 contribution becomes increasingly more important near the HHG cutoff and therefore depends on the laser intensity.