Pure Even Harmonic Generation from Oriented CO in Linearly Polarized Laser Fields

Area of Science:

• Quantum Optics
• Molecular Physics
• Nonlinear Optics

Background:

• High harmonic generation (HHG) typically produces spectra with odd-order harmonics.
• Pure even harmonic generation has been a long-sought but unachieved experimental goal.
• Previous HHG studies focused on atomic or non-polar molecular systems.

Purpose of the Study:

• To investigate the generation of pure even harmonic spectra.
• To explore the role of molecular orientation and permanent dipole moments in HHG.
• To identify conditions for achieving even-harmonic-only emission.

Main Methods:

• Utilized time-dependent density-functional theory (TDDFT) for simulations.
• Employed oriented carbon monoxide (CO) molecules.
• Simulated interactions with linearly polarized laser fields.

Main Results:

• Successfully generated spectra containing only even harmonics.
• Observed pure even harmonic generation when CO molecular axis is perpendicular to laser polarization.
• Demonstrated that polarization of generated harmonics is perpendicular to laser polarization.

Conclusions:

• Pure even harmonic generation is achievable in oriented molecules with permanent dipoles.
• The phenomenon arises from dipole acceleration due to the permanent dipole moment.
• This effect is applicable to various systems with permanent dipoles, including bulk crystals and polyatomic molecules.