Fig. 1: Strong coupling of a gold (Au) nanoslit array coated with a squaraine-based J-aggregated thin film (ProSQ-C16, SQ).
From: Plasmon mediated coherent population oscillations in molecular aggregates
a Experimental geometry. The nanoslit sample is illuminated with a phase-locked pair of pump pulses, separated by the coherence time \(\tau\) at incidence angle \(\theta\). The pump-induced change in sample reflectivity is monitored by a probe pulse with the same incidence angle and time-delayed by the waiting time T. b Linear reflectivity of a 10-nm J-aggregated film of ProSQ-C16 squaraine molecules (inset) on a gold surface. c Experimental, reflective two-dimensional electronic (2DES) spectrum of the film on a flat gold surface at \(T=0\) fs. Bottom: Cross section along the detection energy for excitation at 1.591 eV showing the characteristic dispersive line shape of the J-aggregate exciton. Inset: One-quantum (\(\left|X\right\rangle\)) and two-quantum (\(\left|{XX}\right\rangle\)) excitations contributing to the 2DES exciton peak. d Waiting time dynamics at the maximum (red) and minimum (blue) of the 2DES exciton peak, showing incoherent relaxation dynamics on a 100-fs time scale. e Angle-resolved linear reflectivity spectra reveal the dispersion relations of upper (UP) and lower (LP) polaritons together with an angle-independent peak of “uncoupled” excitons (X). f Finite-difference time domain (FDTD) simulation of the angle-resolved reflectivity.
