Mie Resonances Research Articles

Ultra‐Pure Chiral Third Harmonic Generation Enabled by Mie‐Resonant Dielectric Dimer

AbstractTailoring chiroptical responses at the nanoscale is crucial for on‐chip compact polarization manipulation and enantiomer sensing. Efficient chiral second and third harmonic generation has been successfully demonstrated from bulk materials to metamaterials. Here, pronounced linear and nonlinear circular dichroisms are obtained by rotating a dielectric nanocylinder dimer. It is revealed that the giant chiroptical effects originate from multipolar Mie resonances on the dimer, especially the magnetic dipole resonance. The calculated nonlinear g‐factor can reach −1.975 in the visible regime, indicating an ultra‐pure chiral third harmonic generation in the ultraviolet band. The presented results open new horizons for enhancing and modulating the linear and nonlinear chiroptical responses of nanostructures and can find potential applications in lasing and sensing.

Visual identification of silver ornament by the structural color based on Mie scattering of ZnO spheres

Structural colors originated from Mie scattering of dielectric spheres can be regulated by the coupling effect between them and substrates. Here a rapid visual identification method of silver ornaments was proposed by the coupling effect of ZnO spheres with them. Both simulation and experimental results proved that, by coupling with different metal substrates, the Mie resonance scattering peaks of ZnO spheres with dimeter of 700 nm showed different degrees of redshift, which lead to different structural color appeared when ZnO spheres deposited on different metal surfaces with a similar appearance. A red structural color was displayed on the surface of the real silver ornament and a yellow-green structural color was shown on the surface of the cupronickel ornament. This method is quite simple and low-cost because it only needs to spray the dispersion of ZnO spheres on the ornament surface. Due to the mild chemical properties of the ZnO, covering and erasing ZnO spheres on the surface of silver would not corrode the silver ornament. Finally, an atomizer method was used for portable and daily testing. This work opens new perspectives on the visual identification of silver.

Design and analysis of chiral and achiral metasurfaces with the finite element method.

The rise of metasurfaces to manipulate the polarization states of light motivates the development of versatile numerical methods able to model and analyze their polarimetric properties. Here we make use of a scattered-field formulation well suited to the Finite Element Method (FEM) to compute the Stokes-Mueller matrix of metasurfaces. The major advantage of the FEM lies in its versatility and its ability to compute the optical properties of structures with arbitrary and realistic shapes, and rounded edges and corners. We benefit from this method to design achiral, pseudo-chiral, and chiral metasurfaces with specific polarimetric properties. We compute and analyze their Mueller matrices. The accuracy of this method is assessed for both dielectric and metallic scatterers hosting Mie and plasmonic resonances.

Acoustic coherent perfect absorption based on a PT symmetric coupled Mie resonator system

Parity-time (PT) symmetric coupled resonator systems have exhibited intriguing and unexpected properties in optics and electronics. Here, we extend it to acoustics and report a coupled Mie resonators (MRs) system respecting PT symmetry. The system is constructed with two parallel waveguides connected by an aperture and two MRs placed symmetrically at both sides of the aperture. Instead of using active elements or complex refractive index modulation without gain, we exploit the incident waves of the waveguide as an effective gain so that PT symmetry with balanced loss and gain is realized by only passive materials. Coherent perfect absorption (CPA), which can completely absorb the in-phase excitations with the same intensity provided from two opposite directions, is observed in the PT symmetric phase and at the exceptional point but not in the broken phase. In addition, by varying the relative phase between the two incident waves, the coherent absorption can be tuned from CPA to zero. Our design may provide a flexible platform to research PT symmetry in acoustics and may have applications in tunable noise control, acoustic modulators, and switches.

Optical Bistability in Nanosilicon with Record Low Q-Factor.

We demonstrated optical bistability in an amorphous silicon Mie resonator with a size of ∼100 nm and Q-factor as low as ∼4 by utilizing photothermal and thermo-optical effects. We not only experimentally confirmed the steep intensity transition and the hysteresis in the scattering response from silicon nanocuboids but also established a physical model to numerically explain the underlying mechanism based on temperature-dependent competition between photothermal heating and heat dissipation. The transition between the bistable states offered particularly steep superlinearity of scattering intensity, reaching an effective nonlinearity order of ∼100th power over excitation intensity, leading to the potential of advanced optical switching devices and super-resolution microscopy.

Dielectric light-trapping nanostructure for enhanced light absorption in organic solar cells

Dielectric scatterers where Mie resonances can be excited in both electric and magnetic modes have emerged as a promising candidate for efficient light trapping (LT) in thin-film solar cells. We present that light absorption in organic solar cells (OSCs) can be significantly enhanced by a front-sided incorporation of a core–shell nanostructure consisting of a high-refractive-index dielectric nanosphere array conformally coated with a low-refractive-index dielectric layer. Strong forward light scattering of the all-dielectric LT structure enables the absorption in an organic semiconductor to be remarkably boosted over a broad range of wavelengths, which is attributed to interference of a simultaneous excitation of the electric and magnetic dipole resonant modes. The OSC with the LT structure shows the short-circuit current density (Jsc) of 28.23 mA/cm2, which is 10% higher than that of a flat OSC. We also explore how the LT structure affects scattering cross-sections, spectral multipole resonances, and far-field radiation patterns. The approach described in this work could offer the possibility for the improvement of characteristic performances of various applications, such as other thin-film solar cells, photodiodes, light-emitting diodes, and absorbers.

Laser heating of ferroelectric cubes for tunable electromagnetic properties in metamaterials

In this experimental study, we demonstrate the feasibility of a thermally tunable, resonant dielectric microwave metasurface based on sub-wavelength Mie resonances of ferroelectric dielectric cubes (Calcium titanate, CaTiO3) in which the temperature of the meta-atoms can be locally and dynamically controlled by heating with an optical laser beam over a large range of temperatures and, consequently, values of the dielectric constant of the cube and corresponding resonance frequency of the meta-atoms. This avoids any interference of otherwise necessary heating elements or power supply wires with the propagation of the microwave signal and can be made spatially addressable. The concept scales at least to the THz domain. This contactless approach opens up an alternative avenue to tunability and active control of metamaterials.

Optical Super‐Resonances in Mesoscale Dielectric Cenosphere: Giant Magnetic Field Generations

AbstractResonant light scattering by mesoscale dielectric spheres has received enormous attention and found many interesting applications. The recently emerged field of Mesotronics provides novel opportunities for wavelength‐scaled optics and new fundamental aspects are still being uncovered. It has recently been demonstrated that high‐order Mie resonances can be excited in homogeneous low‐dissipation mesoscale dielectric spheres, leading to the generation of intense magnetic fields. This article describes a simple and effective way to drastically enhance the superresonance effect. Proof‐of‐principle results for the first time show that yet one more novel phenomenon of increasing the intensity of the magnetic field without changing the resonant Mie size parameter of the sphere by introducing an air cavity. In such a dielectric cenosphere (from two Greek words “kenos”‐hollow and “sphaira”‐sphere), by correct choice of the air cavity size, it is possible to increase the intensity of the electromagnetic fields at the poles of the sphere by an order of magnitude due to increasing of the amplitude of resonant partial wave coefficient.

Lattice Mie resonances and emissivity enhancement in mid-infrared iron pyrite metasurfaces.

High-refractive-index antennas with characteristic dimensions comparable to wavelength have a remarkable ability to support pronounces electric and magnetic dipole resonances. Furthermore, periodic arrangements of such resonant antennas result in narrow and strong lattice resonances facilitated by the lattice. We design iron pyrite antennas operating in the mid-infrared spectral range due to the material's low-energy bandgap and high refractive index. We utilize Kirchhoff's law, stating that emissivity and absorptance are equal to each other in equilibrium, and we apply it to improve the thermal properties of the iron pyrite metasurface. Through the excitation of collective resonances and manipulation of the antenna lattice's period, we demonstrate our capacity to control emissivity peaks. These peaks stem from the resonant excitation of electric and magnetic dipoles within proximity to the Rayleigh anomalies. In the lattice of truncated-cone antennas, we observe Rabi splitting of electric and magnetic dipole lattice resonances originating from the antennas' broken symmetry. We demonstrate that the truncated-cone antenna lattices support strong out-of-plane magnetic dipole lattice resonances at oblique incidence. We show that the truncated-cone antennas, as opposed to disks or cones, facilitate a particularly strong resonance and bound state in the continuum at the normal incidence. Our work demonstrates the effective manipulation of emissivity peaks in iron pyrite metasurfaces through controlled lattice resonances and antenna design, offering promising avenues for mid-infrared spectral engineering.

Multipole engineering by displacement resonance: a new degree of freedom of Mie resonance

The canonical studies on Mie scattering unravel strong electric/magnetic optical responses in nanostructures, laying foundation for emerging meta-photonic applications. Conventionally, the morphology-sensitive resonances hinge on the normalized frequency, i.e. particle size over wavelength, but non-paraxial incidence symmetry is overlooked. Here, through confocal reflection microscopy with a tight focus scanning over silicon nanostructures, the scattering point spread functions unveil distinctive spatial patterns featuring that linear scattering efficiency is maximal when the focus is misaligned. The underlying physical mechanism is the excitation of higher-order multipolar modes, not accessible by plane wave irradiation, via displacement resonance, which showcases a significant reduction of nonlinear response threshold, sign flip in all-optical switching, and spatial resolution enhancement. Our result fundamentally extends the century-old light scattering theory, and suggests new dimensions to tailor Mie resonances.

1D Sb2S3 with Strong Mie Resonance Toward Highly‐Sensitive Polarization‐Discriminating Photodetection and Its Application in High‐Temperature‐Proof Imaging and Dual‐Channel Communications

AbstractHigh‐speed and sensitive UV–Vis photodetectors have been constructed based on a typical 1D van der Waals material, antimony sulfide (Sb2S3). Impressively, the Sb2S3 nanowire photodetector demonstrates pronounced photosensitivity exhibiting a remarkable on/off ratio of ≈2800 under a power density of 318 mW cm−2. In addition, a high responsivity, an outstanding detectivity, and a short response/recovery time of 270 A W−1, 4.37 × 1013 Jones, and 10/12 ms are achieved. The competitive photosensitivity is associated with the intrinsic Mie resonance of the Sb2S3 nanowire, which is conducive to enhancing the coupling of the Sb2S3 photosensitive channel with incident light. By virtue of the unique 1D structural nature in both intrinsic and extrinsic perspectives, the Sb2S3 nanowire photodetectors manifest distinct polarization‐discriminating photoresponse with the optimal dichroic ratio reaching ≈7.2. Moreover, the Sb2S3 nanowire photodetectors demonstrate stable photoresponse from room temperature to 160 °C, and these nanodevices are durable against long‐term high‐temperature heating treatment at up to 300 °C. Taking advantage of the excellent thermal robustness, high‐temperature‐proof optoelectronic imaging and dual‐channel optical communication applications are demonstrated based on low‐dimensional van der Waals materials. On the whole, this study provides a new option for an advanced multifunctional optoelectronic system in extreme working environments.

Broadband and strength-switchable circular dichroism in a Ge2Sb2Te5-based metasurface.

Circular dichroism (CD) is highly required in the applications of biological detection and analytical chemistry. In this paper, we achieved a giant, broadband, and strength-switchable CD effect in a quadruple z-shaped G e 2 S b 2 T e 5 (GST) metasurface. At the amorphous state of GST (a-GST), the giant CD reaches 0.92 and the width of the absorption >0.80 is about 100nm. The giant and broadband CD originates from polarization selective excitations of Mie resonances and the coupling between subunit resonators. With the transition from a-GST to crystalline GST, CD could be dynamically switched from 0.92 to 0.05. The GST-based metasurfaces with giant and wide-range switching CD will promote the development of active chiral devices.

Visible Mie resonances in dielectric hollow spheres: Principle, regulation, and applications

AbstractDielectric nanostructures have recently been frequently employed as building blocks for photonic structures due to their advantages, including low energy dissipation, good chemical stability, and distinct resonant properties compared to plasmonic nanostructures. One of the most important principles that governs the optical property of dielectric nanoparticles is Mie resonance, which highly depends on dielectric property, size, morphology, and assembly structures of the nanoparticles as well as the surrounding environment. Among diverse types of Mie‐resonant nanoparticles, hollow spheres are particularly attractive as they can reduce multiple scattering and elongates the mean free path of the light passing through, which results in enhanced Mie resonance compared to solid particles and benefits a broad range of applications including structural color and beyond. This article aims at reviewing the recent development of Mie‐resonant hollow spheres from aspects starting from a brief theoretical introduction of Mie resonance in hollow spheres, principles for regulation of the resonances, followed by common strategies for synthesis, and recent advances in applications of Mie‐resonant hollow spheres. Remarks on the challenges and future opportunities in this area will also be presented.

Light scattering features induced by residual layers in dielectric dewetted nanoparticles

All-dielectric, sub-micrometric particles obtained through solid state dewetting of thin SiGe-films have been shown to support Mie resonances together with a high-quality monocrystalline composition and atomically smooth facets. Recently, a precise study on the impact given by the effective complex morphology of a SiGe dewetted nanoparticle to the Mie scattering properties has been provided and carried on through a novel experimental technique called Dark-field Scanning Optical Microscopy. In this work, by means of the same experimental technique and numerical simulations of light scattering, we show how the presence of a pedestal enriched with silicon placed under the SiGe-nanoparticle results in a sharp peak at high energy in the total scattering cross-section. Exploiting a tilted illumination to redirect scattered light, we are able to discriminate the spatial localization of the pedestal-induced resonance. Our results contribute to extending the practical implementations of dewetted Mie resonators in the field of light scattering directionality, sensing applications and show further engineering options beyond the simple isolated-island case.

Tunable Mie resonance in complex-shaped gadolinium niobate

Nanoscale particles described by Mie resonance in the UV–vis–NIR region are in high demand for optical applications. Controlling the shape and size of these particles is essential, as it results in the ability to control the wavelength of the Mie resonance peak. In this work, we study the extensive scattering properties of gadolinium niobate particles with complex bar- and cube-like shapes in the UV–vis–NIR region. We perform our experimental analysis by characterizing the morphology and extinction spectra, and our theoretical study by implementing a Mie scattering model for a distribution of spherical particles. We can accurately model the size distribution and extinction spectra of complex shaped particles and isolate the contribution of aggregates to the extinction spectra. We can separate the contributions of dipoles, quadrupoles, and octupoles to the Mie resonances for their respective electric and magnetic parts. Our results show that we can tune the broad Mie resonance peak in the extinction spectra by the nanoscale properties of our system. This behavior can aid in the design of lasing and luminescence-enhanced systems. These dielectric gadolinium niobate submicron particles are excellent candidates for light manipulation on the nanoscale.

Epitaxially Grown Silicon Nanowires with a Gold Molecular Adhesion Layer for Core/Shell Structures with Compact Mie and Plasmon Resonances.

Noble-metal plasmonic nanostructures have attracted much attention because they can support deep-subwavelength optical resonances, yet their performance tends to be limited by high Ohmic absorption losses. In comparison, high-index dielectric materials can support low-loss optical resonances but do not tend to yield the same subwavelength optical confinement. Here, we combine these two approaches and examine the dielectric-plasmonic resonances in dielectric/metal core/shell nanowires. Si nanowires were grown epitaxially from (111) substrates, and direct deposition of Au on these structures by physical vapor deposition yielded nonconformal Au islands. However, by introduction of a molecular adhesion layer prior to deposition, cylindrical Si/Au core/shell nanostructures with conformal metal shells were successfully fabricated. Examining these structures as optical cavities using both optical simulations and experimental extinction measurements, we found that the structures support Mie resonances with quality factors enhanced up to ∼30 times compared with pure dielectric structures and plasmon resonances with optical confinement enhanced up to ∼5 times compared with pure metallic structures. Interestingly, extinction spectra of both Mie and plasmon resonances yield Fano line shapes, whose manifestation can be attributed to the combination of high quality factor resonances, Mie-plasmon coupling, and phase delay of the background optical field. This work demonstrates a bottom-up synthetic method for the production of freestanding, cylindrically symmetric semiconductor/metal core/shell nanowires that enables the efficient trapping of light on deep-subwavelength length scales for varied applications in photonics and optoelectronics.

Unveiling Local Optical Properties Using Nanoimaging Phase Mapping in High-Index Topological Insulator Bi2Se3 Resonant Nanostructures.

Topological insulators are materials characterized by an insulating bulk and high mobility topologically protected surface states, making them promising candidates for future optoelectronic and quantum devices. Although their electronic properties have been extensively studied, their mid-infrared (MIR) properties and prospective photonic capabilities have not been fully uncovered. Here, we use a combination of far-field and near-field nanoscale imaging and spectroscopy to study chemical vapor deposition-grown Bi2Se3 nanobeams (NBs). We extract the MIR optical constants of Bi2Se3, revealing refractive index values as high as n ∼ 6.4, and demonstrate that the NBs support Mie resonances across the MIR. Local near-field reflection phase mapping reveals domains of various phase shifts, providing information on the local optical properties of the NBs. We experimentally measure up to 2π phase-shift across the resonance, in excellent agreement with finite-difference time-domain simulations. This work highlights the potential of Bi2Se3 for quantum circuitry, nonlinear generation, high-Q metaphotonics, and photodetection.

Observation of Room-Temperature Exciton-Polariton Emission from Wide-Ranging 2D Semiconductors Coupled with a Broadband Mie Resonator.

Two-dimensional exciton-polaritons in monolayer transition metal dichalcogenides (TMDs) exhibit practical advantages in valley coherence, optical nonlinearities, and even bosonic condensation owing to their light-emission capability. To achieve robust exciton-polariton emission, strong photon-exciton couplings are required at the TMD monolayer, which is challenging due to its atomic thickness. High-quality (Q) factor optical cavities with narrowband resonances are an effective approach but typically limited to a specific excitonic state of a certain TMD material. Herein, we achieve on-demand exciton-polariton emission from a wide range of TMDs at room temperature by hybridizing excitons with broadband Mie resonances spanning the whole visible spectrum. By confining broadband light at the TMD monolayer, our one type of Mie resonator on different TMDs enables enhanced light-matter interactions with multiple excitonic states simultaneously. We demonstrate multi-Rabi splittings and robust polaritonic photoluminescence in monolayer WSe2, WS2, and MoS2. The hybrid system also shows the potential to approach the ultrastrong coupling regime.

Circularly Polarized Scattering Radiation From a Silicon Nanosphere

AbstractA dielectric nanosphere with orthogonal electric dipole (ED) and magnetic dipole (MD) Mie resonances can be a nanoantenna radiating circularly polarized light in specific directions if the amplitudes and the phase relations are properly designed. First, theoretical calculations show that a silicon nanosphere illuminated with a linearly polarized plane wave radiates circularly polarized light at the wavelength in between the ED and MD resonances if the refractive index of a surrounding medium (nm) is ≈1.3; the ellipticity of the scattered light can be >0.99 when nm is in a 1.19–1.35 range. Size‐purified silicon nanospheres suspended in water (nm = 1.33) are then prepared, and the angle‐ and circular‐polarization‐resolved scattering spectra are studied. It is experimentally demonstrated that circularly polarized light is radiated in specific directions under linearly polarized plane wave illumination. The results also show that the wavelength of the radiation of circularly polarized light can be controlled in the whole visible range by controlling the silicon nanosphere diameter in 100–200 nm range.

Understanding the Formation Mechanisms of Silicon Particles from the Thermal Disproportionation of Hydrogen Silsesquioxane.

Crystalline silicon particles sustaining Mie resonances are readily obtained from the thermal processing of hydrogen silsesquioxane (HSQ). Here, the mechanisms involved in silicon particle formation and growth from HSQ are investigated through real-time in situ analysis using an environmental transmission electron microscope and X-ray diffractometer. The nucleation of Si nanodomains is observed starting around 1000 °C. For the first time, a highly mobile intermediate phase is experimentally observed, thus demonstrating a previously unknown growth mechanism. At least two growth processes occur simultaneously: the coalescence of small particles into larger particles and growth mode by particle displacement through the matrix toward the HSQ grain surface. Postsynthetic characterization by scanning electron microscopy further supports the latter growth mechanism. The gaseous environment employed during synthesis impacts particle formation and growth under both in situ and ex situ conditions, impacting the particle yield and structural homogeneity. Understanding the formation mechanisms of particles provides promising pathways for reducing the energy cost of this synthetic route.