Epsilon-near-zero substrate-enabled strong coupling between molecular vibrations and mid-infrared plasmons

Area of Science:

• Optics and Photonics
• Chemical Physics
• Materials Science

Background:

• Vibrational strong coupling (VSC) involves strong light-matter interactions between molecular vibrations and optical resonant modes.
• VSC has the potential to modify molecular chemistry and control ground-state chemical reactions.
• Achieving VSC typically requires efficient coupling between molecular vibrations and plasmonic resonances.

Purpose of the Study:

• To realize VSC between organic molecular vibrations and mid-infrared plasmons on metallic antennas.
• To investigate the role of an epsilon-near-zero (ENZ) substrate in facilitating VSC.
• To explore methods for controlling the molecule-plasmon coupling strength.

Main Methods:

• Utilizing quartz as an ENZ substrate to create sharp mid-infrared plasmonic resonances.
• Coupling these plasmonic resonances with the molecular vibrations of polymethyl methacrylate (PMMA).
• Investigating the dependence of coupling strength on PMMA layer thickness and incident light polarization.

Main Results:

• Demonstrated VSC between PMMA molecular vibrations and mid-infrared plasmons on metallic antennas.
• The ENZ substrate enabled high-Q plasmonic resonances (Q factor ~50).
• Coupling strength scaled with the square root of PMMA thickness, reaching the VSC regime at ~300 nm.
• Molecule-plasmon coupling was found to be polarization-dependent.

Conclusions:

• This work presents a novel approach for achieving VSC using metallic antennas and an ENZ substrate.
• The findings offer a new pathway for controlling molecule-plasmon interactions.
• This technique holds promise for enhancing the sensitivity of molecular vibrational spectroscopy.