On the Nonlinear Excitation of Phononic Frequency Combs in Molecules

TL;DR

This paper proposes a theoretical method to generate phononic frequency combs in polar molecules like CO by exploiting their permanent dipole moments, opening new possibilities in molecular science.

Contribution

It introduces a novel approach for creating phononic combs in molecules using rovibronic excitation and permanent dipole moments, expanding the scope beyond mechanical resonators.

Findings

Demonstrated the role of permanent dipole moments in phononic comb generation

Showed that rovibronic excitation can produce PFCs without electronic excitation

Extended phononic comb concepts from mechanical systems to molecular systems

Abstract

The mechanical analog of optical frequency combs, phononic frequency combs (PFCs), has recently been demonstrated in mechanical resonators via nonlinear coupling among multiple phonon modes. However, for exciting phononic combs in molecules, the requisite strong nonlinear couplings need not be readily present. To overcome this limitation, this paper introduces an alternative route for the generation of phononic combs in polar molecules. Theoretically, we investigated the radiation and phononic spectra generated from CO molecule possessing relatively large permanent dipole moment with density matrix formalism. By considering rovibronic excitation of the ground-state CO molecule while avoiding the electronic excitation, the contribution of the permanent dipole moment and electric dipole polarizability to the creation of PFCs is demonstrated and distinguished. The finding could motivate the possible extension of combs to molecular systems to offer new avenues in molecular sciences.