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Modified relaxation dynamics and coherent energy exchange in coupled vibration-cavity polaritons

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ABSTRACT

Coupling vibrational transitions to resonant optical modes creates vibrational polaritons shifted from the uncoupled molecular resonances and provides a convenient way to modify the energetics of molecular vibrations. This approach is a viable method to explore controlling chemical reactivity. In this work, we report pump–probe infrared spectroscopy of the cavity-coupled C–O stretching band of W(CO)6 and the direct measurement of the lifetime of a vibration-cavity polariton. The upper polariton relaxes 10 times more quickly than the uncoupled vibrational mode. Tuning the polariton energy changes the polariton transient spectra and relaxation times. We also observe quantum beats, so-called vacuum Rabi oscillations, between the upper and lower vibration-cavity polaritons. In addition to establishing that coupling to an optical cavity modifies the energy-transfer dynamics of the coupled molecules, this work points out the possibility of systematic and predictive modification of the excited-state kinetics of vibration-cavity polariton systems.

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Experimental schematic and frequency-domain spectra.(a) Schematic of sample comprising two dielectric mirrors separated by a PTFE spacer and filled with the solution of interest. (b) Dispersion of the infrared transmission of a cavity filled with 10 mM W(CO)6 in hexane. The pink line corresponds to the position of the infrared-active C–O stretch at 1,983 cm−1. (c) Red points are the measured intensity of the probe pulse transmitted through the cavity in b, showing the UP and LP bands separated by the effective splitting. Blue trace is the Fourier transform infrared spectrum of W(CO)6 without cavity coupling (5 mM solution in a 25 μm cell comprising CaF2 windows), dominated by the C–O stretch absorption at 1,983 cm−1.
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f1: Experimental schematic and frequency-domain spectra.(a) Schematic of sample comprising two dielectric mirrors separated by a PTFE spacer and filled with the solution of interest. (b) Dispersion of the infrared transmission of a cavity filled with 10 mM W(CO)6 in hexane. The pink line corresponds to the position of the infrared-active C–O stretch at 1,983 cm−1. (c) Red points are the measured intensity of the probe pulse transmitted through the cavity in b, showing the UP and LP bands separated by the effective splitting. Blue trace is the Fourier transform infrared spectrum of W(CO)6 without cavity coupling (5 mM solution in a 25 μm cell comprising CaF2 windows), dominated by the C–O stretch absorption at 1,983 cm−1.

Mentions: Vibration-cavity polaritons may be formed by placing a strong vibrational absorber between two closely spaced mirrors that form a FP cavity (shown schematically in Fig. 1a). For this work, the cavity resonance is angle-tuned through the triply degenerate antisymmetric C–O stretching band (α∼70,000 M−1 cm−1 at 1,983 cm−1) of W(CO)6 in hexane. The full dispersion of the molecule-loaded cavity (Fig. 1b) displays cavity modes that disperse with angle and anti-crossings as the cavity modes tune through resonance with the C–O stretching band (horizontal pink line). Multiple cavity modes are visible due to the cavity's long pathlength (L=25 μm) and relatively narrow free spectral range (150 cm−1). Longer cavities and higher-order modes yield the same coupling as first-order cavities (L=λ/2n, n=1) if the absorber concentration is the same2829. The normal-mode splitting is the minimum separation between the polariton modes and depends on the absorber concentration1529. Transient measurements, discussed below, are performed at the angle of strongest coupling except where noted otherwise. Figure 1c shows the transmission spectrum of the sample at the angle of strongest coupling for a 10 mM solution of W(CO)6 within a FP cavity. The two transmission features correspond to the upper- (UP, 1,994 cm−1) and lower-polariton (LP, 1,970 cm−1) branches, and are separated by the effective splitting, Ω=24 cm−1 in this case.


Modified relaxation dynamics and coherent energy exchange in coupled vibration-cavity polaritons
Experimental schematic and frequency-domain spectra.(a) Schematic of sample comprising two dielectric mirrors separated by a PTFE spacer and filled with the solution of interest. (b) Dispersion of the infrared transmission of a cavity filled with 10 mM W(CO)6 in hexane. The pink line corresponds to the position of the infrared-active C–O stretch at 1,983 cm−1. (c) Red points are the measured intensity of the probe pulse transmitted through the cavity in b, showing the UP and LP bands separated by the effective splitting. Blue trace is the Fourier transform infrared spectrum of W(CO)6 without cavity coupling (5 mM solution in a 25 μm cell comprising CaF2 windows), dominated by the C–O stretch absorption at 1,983 cm−1.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5121416&req=5

f1: Experimental schematic and frequency-domain spectra.(a) Schematic of sample comprising two dielectric mirrors separated by a PTFE spacer and filled with the solution of interest. (b) Dispersion of the infrared transmission of a cavity filled with 10 mM W(CO)6 in hexane. The pink line corresponds to the position of the infrared-active C–O stretch at 1,983 cm−1. (c) Red points are the measured intensity of the probe pulse transmitted through the cavity in b, showing the UP and LP bands separated by the effective splitting. Blue trace is the Fourier transform infrared spectrum of W(CO)6 without cavity coupling (5 mM solution in a 25 μm cell comprising CaF2 windows), dominated by the C–O stretch absorption at 1,983 cm−1.
Mentions: Vibration-cavity polaritons may be formed by placing a strong vibrational absorber between two closely spaced mirrors that form a FP cavity (shown schematically in Fig. 1a). For this work, the cavity resonance is angle-tuned through the triply degenerate antisymmetric C–O stretching band (α∼70,000 M−1 cm−1 at 1,983 cm−1) of W(CO)6 in hexane. The full dispersion of the molecule-loaded cavity (Fig. 1b) displays cavity modes that disperse with angle and anti-crossings as the cavity modes tune through resonance with the C–O stretching band (horizontal pink line). Multiple cavity modes are visible due to the cavity's long pathlength (L=25 μm) and relatively narrow free spectral range (150 cm−1). Longer cavities and higher-order modes yield the same coupling as first-order cavities (L=λ/2n, n=1) if the absorber concentration is the same2829. The normal-mode splitting is the minimum separation between the polariton modes and depends on the absorber concentration1529. Transient measurements, discussed below, are performed at the angle of strongest coupling except where noted otherwise. Figure 1c shows the transmission spectrum of the sample at the angle of strongest coupling for a 10 mM solution of W(CO)6 within a FP cavity. The two transmission features correspond to the upper- (UP, 1,994 cm−1) and lower-polariton (LP, 1,970 cm−1) branches, and are separated by the effective splitting, Ω=24 cm−1 in this case.

View Article: PubMed Central - PubMed

ABSTRACT

Coupling vibrational transitions to resonant optical modes creates vibrational polaritons shifted from the uncoupled molecular resonances and provides a convenient way to modify the energetics of molecular vibrations. This approach is a viable method to explore controlling chemical reactivity. In this work, we report pump–probe infrared spectroscopy of the cavity-coupled C–O stretching band of W(CO)6 and the direct measurement of the lifetime of a vibration-cavity polariton. The upper polariton relaxes 10 times more quickly than the uncoupled vibrational mode. Tuning the polariton energy changes the polariton transient spectra and relaxation times. We also observe quantum beats, so-called vacuum Rabi oscillations, between the upper and lower vibration-cavity polaritons. In addition to establishing that coupling to an optical cavity modifies the energy-transfer dynamics of the coupled molecules, this work points out the possibility of systematic and predictive modification of the excited-state kinetics of vibration-cavity polariton systems.

No MeSH data available.


Related in: MedlinePlus