Ellipticity dependence of high-order harmonic generation from aligned molecules

Area of Science:

• Atomic, Molecular, and Optical Physics
• Quantum Chemistry
• Nonlinear Optics

Background:

• High-order harmonic generation (HHG) is a key process in strong-field physics, producing high-energy photons.
• Understanding HHG from molecules is crucial for probing molecular electronic structure and dynamics.
• Previous models often simplified molecular complexities, limiting their applicability.

Purpose of the Study:

• To investigate the ellipticity dependence of HHG from aligned N2, O2, and CO2 molecules.
• To explore the influence of molecular alignment, valence orbital characteristics, and recombination interference on HHG.
• To develop and validate a generalized theoretical model for molecular HHG.

Main Methods:

• Experimental measurements of HHG spectra from aligned N2, O2, and CO2 molecules under varying laser ellipticity.
• Theoretical modeling extending the Lewenstein model with an electron acceleration parameter (xi(theta)).
• Incorporation of molecular orbital methods to account for molecular symmetry and electronic structure.

Main Results:

• Ellipticity dependence of HHG is sensitive to molecular alignment and valence orbital symmetry.
• Destructive interference in the electron-hole recombination pathway significantly impacts the ellipticity dependence.
• The generalized theoretical model successfully reproduces the experimental observations.

Conclusions:

• Molecular alignment and orbital symmetry are critical factors governing HHG ellipticity dependence.
• The developed theoretical framework accurately describes HHG in molecules, including interference effects.
• This work provides a more comprehensive understanding of HHG in molecular systems.