Spanning Strong to Weak Normal Mode Coupling between Vibrational and Fabry–Pérot Cavity Modes through Tuning of Vibrational Absorption Strength

Abstract

Designing coupled vibrational-cavity polariton systems to modify chemical reaction rates and paths requires an understanding of how this coupling depends on system parameters (i.e., absorber strength, modal distribution, and vibrational absorber and cavity line widths). Here, we evaluate the impact of absorption coefficient and cavity design on normal mode coupling between a Fabry–Perot cavity and a molecular vibration. For a vibrational band of urethane in a polymer matrix, the coupling strength increases with its concentration so that the system spans the weak and strong coupling regimes. The experimentally determined Rabi splitting values are in excellent agreement with an analytical expression derived for classical coupled oscillators that includes no fitting parameters. Also, the cavity mode profile is altered through choice of mirror type, with metal mirrors resulting in stronger confinement and thus coupling, while dielectric stack mirrors provide higher transmission for a given cavity quality fact...