# Precise determination of excitation energies in condensed-phase molecular systems based on exciton-polariton measurements

## TL;DR

This paper introduces a method to accurately determine excitation energies in condensed-phase molecular systems by measuring polaritons formed through strong coupling with an optical cavity, accounting for environmental thermal fluctuations.

## Contribution

It presents a novel approach using exciton-polariton measurements to precisely determine excitation energies, including analysis of environmental effects on polariton linewidths.

## Key findings

- Power scaling law relates polariton linewidth to molecule number.
- Environmental thermal fluctuations influence polariton properties.
- Method improves accuracy of excitation energy measurements.

## Abstract

The precise determination of the excitation energies in condensed-phase molecular systems is important for understanding system-environment interactions as well as for the prerequisite input data of theoretical models used to study the dynamics of the system. The excitation energies are usually determined by fitting of the measured optical spectra that contain broad and unresolved peaks as a result of the thermally random dynamics of the environment. Herein, we propose a method for precise energy determination by strongly coupling the molecular system to an optical cavity and measuring the energy of the resulting polariton. The effect of thermal fluctuations induced by the environment on the polariton is also investigated, from which a power scaling law relating the polariton's linewidth to the number of molecules is obtained. The power exponent gives important information about the environmental dynamics.