Ultrafast vibrational excitation transfer on resonant antenna lattices revealed by two-dimensional infrared spectroscopy

Abstract

High-quality lattice resonances in arrays of infrared antennas operating in an open-cavity regime form polariton states by means of strong coupling to molecular vibrations. We studied polaritons formed by carbonyl stretching modes of (poly)methyl methacrylate on resonant antenna arrays using femtosecond 2DIR spectroscopy. At a normal incidence of excitation light, doubly-degenerate antenna-lattice resonances (ALR) form two polariton states: a lower polariton and an upper polariton. At an off-normal incidence geometry of the 2DIR experiments, the ALR degeneracy is lifted and, consequently, the polariton energies are split. We spectrally resolved and tracked the time-dependent evolution of a cross-peak signal associated with the excitation of reservoir states and the unidirectional transfer of the excess energy to lower polaritons. Bi-exponential decay of the cross-peak suggests that a reversible energy exchange between the bright and dark lower polaritons occurs with a characteristic transfer time of ~200 fs. The cross-peak signal further decays within ~800 fs, which is consistent with the relaxation time of the carbonyl stretching vibration and with the dephasing time of the ALR. An increase in the excitation pulse intensity leads to saturation of the cross-peak amplitude and to a modification of the relaxation dynamics. Using quantum-mechanical modelling, we found that kinetic scheme that captures all the experimental observations implies that only the bright lower polariton accepts the energy from the reservoir, suggesting that transfer occurs via a mechanism involving dipole-dipole interaction. Efficient reservoir-to-polariton transfer can play an important role in developing novel room-temperature quantum optical devices in the mid-infrared wavelength region.

Molecular Vibrational Polariton Dynamics: What Can Polaritons Do?

“…After the first report of the ultrafast IR pump–probe study of MVPs by Dunkelberger, Owrutsky, and co-workers and inspired by theoretical works, our group collaborated with the Naval Research Laboratory group to implement 2D IR spectroscopy to study polariton dynamics. , We showed that 2D IR spectroscopy has unique capabilities to resolve dark modes from polariton states. This method has since been adopted to study pure polaritonic responses and polaritons in open cavity systems. − …”

“…This method has since been adopted to study pure polaritonic responses and polaritons in open cavity systems. 52 − 54 …”

Role of Raman Modes in Polariton Relaxation Process

“…5 Ultrafast spectroscopy of polaritons provides a unique window to reveal how energy of polariton states redistributes into molecular modes and influences the chemistry. Significant works using pump-probe and two-dimensional infrared (2D IR) spectroscopy 6,7 have shown that polaritons can open new pathways for inter-and intra-molecular vibrational energy transfer 8 , as well as hinder isomerization events 9 . Furthermore, results from our group previously showed that for W(CO)6 based MVPs, excited LP and UP underwent different dynamics: UP decayed rapidly and exponentially to the first excited state of dark modes, while LP first transferred to an intermediate state before relaxing to the first excited dark modes, which manifested as an initial rise and then a decay.…”

Vibrational Polaritons in Disordered Molecular Ensembles

“…Experimentally, an open cavity was constructed with a high-quality antenna-lattice resonance (ALR) of the half-wavelength infrared antenna array, 38 , 39 where individual dipolar antenna resonances couple to the in-plane lattice diffraction order. 40 , 41 Unlike the commonly used Fabry–Perot-style optical cavities, in our experiments, the optical extinction occurs only at the ALR frequency while the nearby spectral region remains transparent, thus allowing direct spectroscopic access both to the polaritons and to the reservoir transitions.…”

“…Experimentally, an open cavity was constructed with a high-quality antenna-lattice resonance (ALR) of the half-wavelength infrared antenna array, , where individual dipolar antenna resonances couple to the in-plane lattice diffraction order. , Unlike the commonly used Fabry–Perot-style optical cavities, in our experiments, the optical extinction occurs only at the ALR frequency while the nearby spectral region remains transparent, thus allowing direct spectroscopic access both to the polaritons and to the reservoir transitions . A 3 × 3 mm nearly defect-free antenna array was fabricated by means of electron-beam lithography on a CaF 2 window. − The gold antennas (dimensions of 0.75 × 0.2 × 0.07 μm) were arranged in a rectangular lattice with a longitudinal period (along the antenna axis) of D L = 1.35 μm and a transverse period of D T = 3.8 μm, as shown in Figure a (inset).…”