Understanding Of Light-matter Interaction Research Articles

Intensity-Dependent Optical Response of 2D LTMDs Suspensions: From Thermal to Electronic Nonlinearities.

The nonlinear optical (NLO) response of photonic materials plays an important role in the understanding of light-matter interaction as well as pointing out a diversity of photonic and optoelectronic applications. Among the recently studied materials, 2D-LTMDs (bi-dimensional layered transition metal dichalcogenides) have appeared as a beyond-graphene nanomaterial with semiconducting and metallic optical properties. In this article, we review most of our work in studies of the NLO response of a series of 2D-LTMDs nanomaterials in suspension, using six different NLO techniques, namely hyper Rayleigh scattering, Z-scan, photoacoustic Z-scan, optical Kerr gate, and spatial self-phase modulation, besides the Fourier transform nonlinear optics technique, to infer the nonlinear optical response of semiconducting MoS2, MoSe2, MoTe2, WS2, semimetallic WTe2, ZrTe2, and metallic NbS2 and NbSe2. The nonlinear optical response from a thermal to non-thermal origin was studied, and the nonlinear refraction index and nonlinear absorption coefficient, where present, were measured. Theoretical support was given to explain the origin of the nonlinear responses, which is very dependent on the spectro-temporal regime of the optical source employed in the studies.

A construct modelling approach to characterize chemistry students’ understanding of the nature of light

ABSTRACT Across science disciplines, light is a common tool for measuring, characterizing, and catalysing molecules and molecular processes. Despite the ubiquity of light-based tools, little research has been done to investigate how students understand light and light–matter interactions (LMI). This topic is typically first introduced in first-year undergraduate chemistry courses where students initially encounter the quantum nature of light and matter. How students make sense of this content and transition from classical concepts to quantum concepts is relatively unknown. To gain further insight on how students develop quantum-level conceptions about light, we use a construct modelling approach. This approach is best suited to capture progressions in student understanding. In this study, we begin to model students’ understanding of LMI by first developing a model for the nature of light. Two sets of qualitative interviews were conducted about the particulate nature of light and the wave nature of light. Analysis of interviews resulted in four construct maps, which can provide information to instructors and researchers about the variation in student understanding of the nature of light. Findings from this study have implications for how quantum chemistry is introduced at the postsecondary level.

The emergence of macroscopic currents in photoconductive sampling of optical fields

Photoconductive field sampling enables petahertz-domain optoelectronic applications that advance our understanding of light-matter interaction. Despite the growing importance of ultrafast photoconductive measurements, a rigorous model for connecting the microscopic electron dynamics to the macroscopic external signal is lacking. This has caused conflicting interpretations about the origin of macroscopic currents. Here, we present systematic experimental studies on the signal formation in gas-phase photoconductive sampling. Our theoretical model, based on the Ramo–Shockley-theorem, overcomes the previously introduced artificial separation into dipole and current contributions. Extensive numerical particle-in-cell-type simulations permit a quantitative comparison with experimental results and help to identify the roles of electron-neutral scattering and mean-field charge interactions. The results show that the heuristic models utilized so far are valid only in a limited range and are affected by macroscopic effects. Our approach can aid in the design of more sensitive and more efficient photoconductive devices.

Universal Theory of Light Scattering of Randomly Oriented Particles: A Fluctuational-Electrodynamics Approach for Light Transport Modeling in Disordered Nanostructures.

Disordered nanostructures are commonly encountered in many nanophotonic systems, from colloid dispersions for sensing to heterostructured photocatalysts. Randomness, however, imposes severe challenges for nanophotonics modeling, often constrained by the irregular geometry of the scatterers involved or the stochastic nature of the problem itself. In this Article, we resolve this conundrum by presenting a universal theory of averaged light scattering of randomly oriented objects. Specifically, we derive expansion-basis-independent formulas of the orientation-and-polarization-averaged absorption cross section, scattering cross section, and asymmetry parameter, for single or a collection of objects of arbitrary shape. These three parameters can be directly integrated into traditional unpolarized radiative energy transfer modeling, enabling a practical tool to predict multiple scattering and light transport in disordered nanostructured materials. Notably, the formulas of average light scattering can be derived under the principles of fluctuational electrodynamics, allowing the analogous mathematical treatment to the methods used in thermal radiation, nonequilibrium electromagnetic forces, and other associated phenomena. The proposed modeling framework is validated against optical measurements of polymer composite films with metal-oxide microcrystals. Our work may contribute to a better understanding of light–matter interactions in disordered systems, such as plasmonics for sensing and photothermal therapy, photocatalysts for water splitting and CO2 dissociation, photonic glasses for artificial structural colors, and diffuse reflectors for radiative cooling, to name just a few.

Anisotropic optical responses of layered thallium arsenic sulfosalt gillulyite

Multi-element two-dimensional (2D) materials hold great promise in the context of tailoring the physical and chemical properties of the materials via stoichiometric engineering. However, the rational and controllable synthesis of complex 2D materials remains a challenge. Herein, we demonstrate the preparation of large-area thin quaternary 2D material flakes via mechanical exfoliation from a naturally occurring bulk crystal named gillulyite. Furthermore, the anisotropic linear and nonlinear optical properties including anisotropic Raman scattering, linear dichroism, and anisotropic third-harmonic generation (THG) of the exfoliated gillulyite flakes are investigated. The observed highly anisotropic optical properties originate from the reduced in-plane crystal symmetry. Additionally, the third-order nonlinear susceptibility of gillulyite crystal is retrieved from the measured thickness-dependent THG emission. We anticipate that the demonstrated strong anisotropic linear and nonlinear optical responses of gillulyite crystal will facilitate the better understanding of light-matter interaction in quaternary 2D materials and its implications in technological innovations such as photodetectors, frequency modulators, nonlinear optical signal processors, and solar cell applications.

Polarization-dependent optical responses in natural 2D layered mineral teallite

Multi-element layered materials enable the use of stoichiometric variation to engineer their optical responses at subwavelength scale. In this regard, naturally occurring van der Waals minerals allow us to harness a wide range of chemical compositions, crystal structures and lattice symmetries for layered materials under atomically thin limit. Recently, one type of naturally occurring sulfide mineral, ternary teallite has attained significant interest in the context of thermoelectric, optoelectronic, and photovoltaic applications, but understanding of light-matter interactions in such ternary teallite crystals is scarcely available. Herein, polarization-dependent linear and nonlinear optical responses in mechanically exfoliated teallite crystals are investigated including anisotropic Raman modes, wavelength-dependent linear dichroism, optical band gap evolution, and anisotropic third-harmonic generation (THG). Furthermore, the third-order nonlinear susceptibility of teallite crystal is estimated using the thickness-dependent THG emission process. We anticipate that our findings will open the avenue to a better understanding of the tailored light-matter interactions in complex multi-element layered materials and their implications in optical sensors, frequency modulators, integrated photonic circuits, and other nonlinear signal processing applications.

Simulation of Solar Cells with Integration of Optical Nanoantennas.

The evolution of nanotechnology has provided a better understanding of light-matter interaction at a subwavelength scale and has led to the development of new devices that can possibly play an important role in future applications. Nanoantennas are an example of such devices, having gained interest in recent years for their application in the field of photovoltaic technology at visible and infrared wavelengths, due to their ability to capture and confine energy of free-propagating waves. This property results from a unique phenomenon called extraordinary optical transmission (EOT) where, due to resonant behavior, light passing through subwavelength apertures in a metal film can be transmitted in greater orders of magnitude than that predicted by classical theories. During this study, 2D and 3D models featuring a metallic nanoantenna array with subwavelength holes coupled to a photovoltaic cell are simulated using a Finite Element Tool. These models present with slight variations between them, such as the position of the nanoantenna within the structure, the holes’ geometry and the type of cell, in order to verify how its optical response is affected. The results demonstrate that the coupling of nanoantennas to solar cells can be advantageous and improve the capture and absorption of radiation. It is concluded that aperture nanoantennas may concentrate radiation, meaning that is possible to tune the electric field peak and adjust absorption on the main layers. This may be important because it might be possible to adjust solar cell performance to the global regions’ solar spectrum by only adjusting the nanoantenna parameters.

Stimulated Chiral Light-Matter Interactions in Biological Microlasers.

Chiral light-matter interactions have emerged as a promising area in biophysics and quantum optics. Great progress in enhancing chiral light-matter interactions have been investigated through passive resonators or spontaneous emission. Nevertheless, the interaction between chiral biomolecules and stimulated emission remains unexplored. Here we introduce the concept of a biological chiral laser by amplifying chiral light-matter interactions in an active resonator through stimulated emission process. Green fluorescent proteins or chiral biomolecules encapsulated in Fabry-Perot microcavity served as the gain material while excited by either left-handed or right-handed circularly polarized pump laser. Owing to the nonlinear pump energy dependence of stimulated emission, significant enhancement of chiral light-matter interactions was demonstrated. Detailed experiments and theory revealed that a lasing dissymmetry factor is determined by molecular absorption dissymmetry factor at its excitation wavelength. Finally, chirality transfer was investigated under a stimulated emission process through resonance energy transfer. Our findings elucidate the mechanism of stimulated chiral light-matter interactions, providing better understanding of light-matter interaction in biophysics, chiral sensing, and quantum biophotonics.

Gauge freedom, quantum measurements, and time-dependent interactions in cavity QED

The interaction between the electromagnetic field inside a cavity and natural or artificial atoms has played a crucial role in developing our understanding of light-matter interaction, and is central to various quantum technologies. Recently, new regimes beyond the weak and strong light-matter coupling have been explored in several settings. These regimes, where the interaction strength is comparable (ultrastrong) or even higher (deep-strong) than the transition frequencies in the system, can give rise to new physical effects and applications. At the same time, they challenge our understanding of cavity QED. When the interaction strength is so high, fundamental issues like the proper definition of subsystems and of their quantum measurements, the structure of light-matter ground states, or the analysis of time-dependent interactions are subject to ambiguities leading to even qualitatively distinct predictions. The resolution of these ambiguities is also important for understanding and designing next-generation quantum devices that will exploit the ultrastrong coupling regime. Here we discuss and provide solutions to these issues.

Manipulating the light-matter interaction in a topological photonic crystal heterostructure.

We theoretically and numerically investigate the ligh-matter interaction in a classic topological photonic crystal (PhC) heterostructure, which consists of two opposite-facing 4-period PhCs spaced by a dielectric layer. Due to the excitation of topological edge mode (TEM) at the interface of the two PhCs, the strong coupling between incident light and TEM produces a high quality resonance peak, which can be applied to many optical devices. As a refractive index sensor, it achieves a sensitivity of 254.5 nm/RIU and a high figure of merit (> 250), which is superior to many previously reported sensors. We further study the coupling between photons and excitons by replacing the pure dielectric layer with the J-aggregates doped layer. By tuning the thickness of the doped layer and the angle of incident light, the dispersive TEM can efficiently interact with the molecular excitons to form a hybrid mode with TEM-like or exciton-like components, showing interesting energy transfer characteristics and flexible modulation characteristics. This work may be helpful for a better understanding of light-matter interactions in a topological PhC heterostructure, and achieve potential applications in related optical devices.

Designer Bloch plasmon polariton dispersion in grating-coupled hyperbolic metamaterials

Hyperbolic metamaterials (HMMs) represent a novel class of fascinating anisotropic plasmonic materials, supporting highly confined propagating plasmon polaritons in addition to surface plasmon polaritons. However, it is very challenging to tailor and excite these modes at optical frequencies by prism coupling because of the intrinsic difficulties in engineering non-traditional optical properties with artificial nanostructures and the unavailability of high refractive index prisms for matching the momentum between the incident light and the guided modes. Here, we report the mechanism of excitation of high-k Bloch-like Plasmon Polariton (BPPs) modes with ultrasmall modal volume using a meta-grating, which is a combined structure of a metallic diffraction grating and a type II HMM. We show how a 1D plasmonic grating without any mode in the infrared spectral range, if coupled to a HMM supporting high-k modes, can efficiently enable the excitation of these modes via coupling to far-field radiation. Our theoretical predictions are confirmed by reflection measurements as a function of angle of incidence and excitation wavelength. We introduce design principles to achieve a full control of high-k modes in meta-gratings, thus enabling a better understanding of light-matter interaction in this type of hybrid meta-structures. The proposed spectral response engineering is expected to find potential applications in bio-chemical sensors, integrated optics and optical sub-wavelength imaging.

Coherent interaction between free electrons and a photonic cavity.

Advances in the research of interactions between ultrafast free electrons and light have introduced a previously unknown kind of quantum matter, quantum free-electron wavepackets1-5. So far, studies of the interactions of cavity-confined light with quantum matter have focused on bound electron systems, such as atoms, quantum dots and quantum circuits, which are considerably limited by their fixed energy states, spectral range and selection rules. By contrast, quantum free-electron wavepackets have no such limits, but so far no experiment has shown the influence of a photonic cavity on quantum free-electron wavepackets. Here we develop a platform for multidimensional nanoscale imaging and spectroscopy of free-electron interactions with photonic cavities. We directly measure the cavity-photon lifetime via a coherent free-electron probe and observe an enhancement of more than an order of magnitude in the interaction strength relative to previous experiments of electron-photon interactions. Our free-electron probe resolves the spatiotemporal and energy-momentum information of the interaction. The quantum nature of the electrons is verified by spatially mapping Rabi oscillations of the electron spectrum. The interactions between free electrons and cavity photons could enable low-dose, ultrafast electron microscopy of soft matter or other beam-sensitive materials. Such interactions may also open paths towards using free electrons for quantum information processing and quantum sensing. Future studies could achieve free-electron strong coupling6,7, photon quantum state synthesis8 and quantum nonlinear phenomena such as cavity electro-optomechanics9.

Experimental and Theoretical Observation of Photothermal Chirality in Gold Nanoparticle Helicoids.

Single-particle spectroscopy is central to the characterization of plasmonic nanostructures and understanding of light-matter interactions in chiral nanosystems. Although chiral plasmonic nanostructures are generally characterized by their circular differential extinction and scattering, single-particle absorption studies can extend our understanding of light-matter interactions. Here, we introduce an experimental observation of photothermal chirality which originated from circular differential absorption of chiral plasmonic nanostructures. Using luminescence ratio thermometry, we identify the optical and photothermal handedness and an absolute temperature difference of 6 K under the right and left circularly polarized light. We observe a circular differential extinction parameter (gext) of -0.13 in colloidally prepared gold helicoids and compare our findings with numerical simulations using finite element methods. The simulated data showed that circular differential absorption and the maximum temperature of a small cluster of helical nanoparticles are polarization-dependent. We observed an intensity-dependent photothermal g-factor from chiral helicoids that decreases slightly at higher temperatures. We also measure a range of optical g-factors from several gold helicoids, which are attributed to the heterogeneity of helicoids in nanoparticles during synthesis. The principles of differential photothermal response of chiral nanomaterials and heat generation described here can be potentially used for thermal photocatalysis, energy conversion, and electronic applications.

An exploration of chemistry students’ conceptions of light and light-matter interactions in the context of the photoelectric effect

ABSTRACT Light is used ubiquitously across science and engineering to explore, characterise, understand matter, and catalyse processes. Relative to its utility in science and engineering, very little research has been conducted on how students develop an understanding of light-matter interactions, especially at the quantum level, which is necessary to understand many modern applications. To begin addressing this gap, we present results from a cross-sectional qualitative investigation of postsecondary chemistry students’ conceptions of light and light-matter interactions in the context of the photoelectric effect. A knowledge analysis of the interviews resulted in a model of students’ understanding that consisted of three distinct levels of knowledge. These levels were distinct from each other based on the features of students’ cognitive structure and treatment of wave-particle duality. The lowest level reasoning constructed fragmented explanations and relied on intuition; and described light behaviour as only a wave or a particle. In contrast, the highest level reasoning coordinated observations and inferences to construct mechanistic explanations of the photoelectric effect; and described light behaviour as both wave and particle. These results provide a starting point for characterising how students conceptually transition from the classical, macroscopic view to the quantum view.

Selective excitation and enhancement of multipolar resonances in dielectric nanospheres using cylindrical vector beams

Resonant excitation and manipulation of complex interactions among two or more resonances in high-index dielectric nanostructures provide great opportunities for engineering novel optical phenomena and applications. However, difficulties often arise when interpreting the observed spectra because of the overlap of the broad resonances contributed by many factors such as particle size, shape, and background index. Therefore, selective excitation of resonances that spectrally overlap with each other provides a gateway towards an improved understanding of the complex interactions. Here, we demonstrate selective excitation and enhancement of multipolar resonances of silicon nanospheres using cylindrical vector beams (CVBs) with different diameters of nanospheres and numerical apertures (NAs) of the excitations. By combining single particle spectroscopy and electrodynamic simulations, we show that the radially polarized beam can selectively excite the electric multipoles, whereas the azimuthally polarized beam can selectively excite the magnetic multipoles even though multipolar resonances are convoluted together due to their spectral overlap. Moreover, focusing the CVBs with high NA can lead to a dominant longitudinal polarization of the electric or magnetic field. We show that the enhanced longitudinal polarization with increasing NA of the radially and azimuthally polarized beams can selectively enhance the electric and magnetic multipolar resonances, respectively. Our approach can be used as a spectroscopy tool to enhance and identify multipolar resonances leading to a better understanding of light-matter interactions in other dielectric nanostructures as well as serve as a first step toward excitation of dark mode and Fano resonances in dielectric oligomers by breaking the symmetry of the nanostructures.

Atomically Thin Nonlinear Transition Metal Dichalcogenide Holograms.

Nonlinear holography enables optical beam generation and holographic image reconstruction at new frequencies other than the excitation fundamental frequency, providing pathways toward unprecedented applications in optical information processing and data security. So far, plasmonic metasurfaces with the thickness of tens of nanometers have been mostly adopted for realizing nonlinear holograms with the potential of on-chip integration but suffering from low conversion efficiency and high absorption loss. Here, we report a nonlinear transition metal dichalcogenide (TMD) hologram with high conversion efficiency and atomic thickness made of only single nanopatterned tungsten disulfide (WS2) monolayer, for producing optical vortex beams and Airy beams as well as reconstructing complex holographic images at the second harmonic (SH) frequency. Our concept of nonlinear TMD holograms paves the way toward not only the understanding of light-matter interactions at the atomic level but the integration of functional TMD-based devices with atomic thickness into the next-generation photonic circuits for optical communication, high-density optical data storage, and information security.

Optical Transmission of an Atomic Vapor in the Mesoscopic Regime.

By measuring the transmission of near-resonant light through an atomic vapor confined in a nanocell we demonstrate a mesoscopic optical response arising from the nonlocality induced by the motion of atoms with a phase coherence length larger than the cell thickness. Whereas conventional dispersion theory-where the local atomic response is simply convolved by the Maxwell-Boltzmann velocity distribution-is unable to reproduce the measured spectra, a model including a nonlocal, size-dependent susceptibility is found to be in excellent agreement with the measurements. This result improves our understanding of light-matter interaction in the mesoscopic regime and has implications for applications where mesoscopic effects may degrade or enhance the performance of miniaturized atomic sensors.

Theoretical and experimental investigation of haze in transparent aerogels.

Haze in optically transparent aerogels severely degrades the visual experience, which has prevented their adoption in windows despite their outstanding thermal insulation property. Previous studies have primarily relied on experiments to characterize haze in aerogels, however, a theoretical framework to systematically investigate haze in porous media is lacking. In this work, we present a radiative transfer model that can predict haze in aerogels based on their physical properties. The model is validated using optical characterization of custom-fabricated, highly-transparent monolithic silica aerogels. The fundamental relationships between the aerogel structure and haze highlighted in this study could lead to a better understanding of light-matter interaction in a wide range of transparent porous materials and assist in the development of low-haze silica aerogels for high-performance glazing units to reduce building energy consumption.

Transient Optical Characteristics of Broad Absorption Band Excitons Modulated by Micro-cavity

The understanding of light-matter interaction within micro-cavity lays the basic groundwork for many future photon-related technologies and applications. We prepared low quality metal-insulator-metal(MIM) micro-cavity consisting massive two-level broad absorption band dye(Nile Red) excitons, which randomly dispersed in SU-8 polymer negative resist matrix and measured their optical characteristics. New binate transmission peaks with large energy separation(so-called Rabi-splitting phenomenon) and their angular anti-crossing behavior in con-sequence of the interaction between dye excitons and confined photons were observed. It was also confirmed that the separated energy can be tuned by changing the doped exciton concentrations. Time-resolved transient absorption measurements showed that such an interaction is indeed a coherent one but rather a strong coupling one and one can modulate such a coherent mechanism by easily adjusting the detuning between dye excitons and confined cavity photons. This work may provide a comprehensive and deep understanding for such massive broad absoprtion band excitons-doped MIM micro-cavities and represent a further step to realize optical cavity-modulated devices in future.

Multi-mode ultra-strong coupling in circuit quantum electrodynamics

With the introduction of superconducting circuits into the field of quantum optics, many experimental demonstrations of the quantum physics of an artificial atom coupled to a single-mode light field have been realized. Engineering such quantum systems offers the opportunity to explore extreme regimes of light-matter interaction that are inaccessible with natural systems. For instance the coupling strength g can be increased until it is comparable with the atomic or mode frequency ωa,m and the atom can be coupled to multiple modes which has always challenged our understanding of light-matter interaction. Here, we experimentally realize a transmon qubit in the ultra-strong coupling regime, reaching coupling ratios of g/ωm = 0.19 and we measure multi-mode interactions through a hybridization of the qubit up to the fifth mode of the resonator. This is enabled by a qubit with 88% of its capacitance formed by a vacuum-gap capacitance with the center conductor of a coplanar waveguide resonator. In addition to potential applications in quantum information technologies due to its small size, this architecture offers the potential to further explore the regime of multi-mode ultra-strong coupling.