United States

An optical microcavity is an interesting tool to study light-matter interaction, e.g. the coupling of a quantum emitter to the optical field in a microcavity. The coupling rate is a measure of the interaction strength between the quantum emitter and cavity mode, and can be used to differentiate between weak or strong coupling.1 
Here, we demonstrate a strongly coupled hybrid system consisting of a thin molecular film of TDBC J-aggregate inside an optical sub-wavelength microresonator coupled to a second microresonator. This hybrid structure combines strong coupling of purely optical modes with strong light-matter interaction.2 The coupling strength and damping of the hybrid system can be tuned by the optical microresonator modes, the lateral position of the TDBC film in the microresonator, and the TDBC concentration in the film. The design of the coupled microresonators allows tuning the resonance of one microcavity across the other, which enables to study the dispersion of the strongly coupled system without tilting of the sample.3 The Rabi splitting of the molecule/cavity hybrid system depends on the position and the number of coherently coupled molecules in the coupled microresonator.2,4 We illustrate this dependence by adjusting the position of TDBC thin film in the coupled microresonator and by reducing the number of molecules by photobleaching. Finally, we will show that the transmission spectrum of the coupled system can be theoretically modeled by coupled damped harmonic oscillators and find an excellent agreement between experiment and theory. 


AIPP Photonics in Chemical Physics

Combining optical strong mode coupling with polaritonic coupling in a λ/2 Fabry Pérot microresonator

tbdc j-aggregate

fabry pérot microresonator

strong coupling

spectroscopy

The 65th Annual Conference on Magnetism and Magnetic Materials (MMM 2020) was held in a virtual form. The COVID-19 pandemic, with its associated uncertainty about international travel and the ability to gather in large groups, meant that the Steering Committee decided to cancel the face-to-face meeting that had been planned in Palm Beach, Florida November 2-6, 2020.

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MMM 2020

poster

The field of photonics, broadly defined, ranges from basic physical work on lasers and ultrashort laser pulses to applications in healthcare, communications, and materials. With its increasingly diverse disciplines and subdisciplines, photonics has become a key component in modern society. The scientific program consists of cross-disciplinary researchers, including chemists, physicists, and engineers, in both theory and experimentation. These researchers will discuss this rapidly expanding field and cover topics that address the latest advances in photonics related research and debate the current needs and priorities, as well as the emerging areas.

To access the AIPP Photonics in Chemical Physics conference, [please remember to register.  ](https://services.aip.org/AIPPHorizons/?confID=3351210)

The field of photonics, broadly defined, ranges from basic physical work on lasers and ultrashort laser pulses to applications in healthcare, communications, and materials. With its increasingly diverse disciplines and subdisciplines, photonics has become a key component in modern society. 

Controlling light-matter interaction with molecular vibrations in mid-infrared resonators offers exciting new research opportunities in chemistry and physics [1]. Laboratory implementations use standard materials, operate at room temperature, and use traditional fabrication and detection techniques, yet they have deeply challenged our fundamental understanding on the connections between cavity quantum electrodynamics and chemistry. We have developed rigorous microscopic quantum theory to describe the optical and chemical properties of realistic molecular vibrations in infrared cavity resonators with non-perturbative light-matter interaction [2,3]. We can successfully describe the linear and nonlinear spectra of vibrational polaritons [4]—hybrid vibration-cavity eigenstates– and realistically study the dissociation dynamics of cavity-coupled molecular bonds under non-adiabatic conditions [5]. The role of symmetry of the ground state electronic density with respect to nuclear displacements in the dynamics of vibrational polaritons is discussed, and future applications of these systems for the generation of THz quantum light are suggested.

Strong light-matter coupling with molecular vibrations in infrared resonators

Donor-bridge-acceptor systems based on boron dipyrromethene (BODIPY) are attractive candidates for bio-imagining and sensing applications because of their sensitivity to temperature, micro-viscosity and solvent polarity. The optimization of the properties of such molecular sensors requires detailed knowledge of the relation between the structure and the photophysical behavior in different environments. In this work, we have investigated the excited-state dynamics of three acceptor-donor-acceptor molecules based on benzodithiophene and BODIPY in solvents of different polarities using a combination of ultrafast spectroscopy and DFT-based electronic structure calculations. Transient absorption spectra show that upon photoexcitation an initial excited species with an induced absorption band in the near-infrared regime is formed independently of the solvent polarity. The subsequent photophysical processes strongly depend on the solvent polarity. In non-polar toluene, this initial excited state undergoes a structural relaxation leading to a delocalized state with partial charge transfer character, while in the more polar tetrahydrofuran a fully charge-separated state is formed. The results clearly show how factors such as donor-acceptor distance and restricted rotational motion by steric hindrance can be used to tune the excited state photophysics to optimize such systems for specific applications.

Excited state dynamics of BODIPY-based acceptor–donor–acceptor systems: a combined experimental and computational study

Effects of electron-vibrational interaction in equilibrium and hot polariton luminescence in microcavities

We found that the time-resolved photoluminescence (TRPL), probed from the imperfection-free CH3NH3PbBr3 crystal bulk, is characterized by a two-stage model (Fig. 1a) that indicates excited phase evolution. Each stage decays following mono-exponential function, and reprents rapid thermal dissociation of the initially generated electron-hole (e-h) pairs and the steady decay of the subsequently formed e-h plamas, respectively. The buffering region (shadowed in red) in between represents the evolving from the dissociated electrons and holes toward the metastable e-h plasmas, similar to previous observations.2 Droplet characters shown by the exciting power threshold (PT) and optically hysteresis are observed (Fig. 1b) for the the largely red-shifted bulk emission with asymmetric spectral line-shape that extends far toward lower energies (inset, Fig. 1a). At certain exciting intensity, the luminescence approached from a more intense exciting power is greater than that reached by in the forward way. We realized and confirmed the occurrence of e-h liquid (EHL) which–most likely–is a cloud of droplets in CH3NH3PbBr3. This not only betters our understanding on halide perovskites but also promotes the search for room-temeprature EHL.3



Excited phase evolution and electron-hole droplets in CH3NH3PbBr3 crystal

Stepwise two-photon absorption (2PA) processes are becoming an important technique because it can achieve high reductive photochemical reactions with visible and near infrared light and intensity-gated high spatiotemporal selectivity with much lower power thresholds than those of the simultaneous 2PA. However, excited states generated by stepwise 2PA (higher excited states and excited states of transient species) are so short-lived that the efficiency for the stepwise 2PA induced photochemical reactions is usually quite low, which limits the versatility for this technique. Here, we demonstrated that the electron of the higher excited state can be efficiently extracted in a nanohybrid of organic molecules and wide bandgap semiconductor nanocrystals (NCs).1 Using perylene bisimide (PBI)-coordinated CdS NCs as a model compound, we demonstrated that the electron of the higher excited state of PBI generated by stepwise 2PA can be extracted to the conduction band of CdS NCs with a quantum yield of ∼0.5–0.7. Moreover, the extracted electron survives at the conduction band of CdS NCs over nanoseconds, which is more than hundred times longer than the lifetime of the higher excited state of PBI. This method can be applied to other organic molecules and larger wide bandgap semiconductors, and therefore, will expand the versatility for the photochemical reactions utilizing the short-lived excited states.

Green and far-red-light induced electron injection from perylene bisimide to wide-bandgap semiconductor nanocrystals with stepwise two-photon absorption process

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