Magneto-Plasmonics and Resonant Interaction of Light with Dynamic Magnetisation in Metallic and All-Magneto-Dielectric Nanostructures

Inert gas condensation made bimetallic FeCu nanoparticles – plasmonic response and magnetic ordering

Bimetallic FeCu nanoparticles of narrow size distribution produced by inert gas condensation (IGC) technique exhibit functional plasmonic and magnetic properties and can be considered as a promising system for the development of biosensors.

Acoustic, Phononic, Brillouin Light Scattering and Faraday Wave-Based Frequency Combs: Physical Foundations and Applications

Frequency combs (FCs)-spectra containing equidistant coherent peaks-have enabled researchers and engineers to measure the frequencies of complex signals with high precision, thereby revolutionising the areas of sensing, metrology and communications and also benefiting the fundamental science. Although mostly optical FCs have found widespread applications thus far, in general FCs can be generated using waves other than light. Here, we review and summarise recent achievements in the emergent field of acoustic frequency combs (AFCs), including phononic FCs and relevant acousto-optical, Brillouin light scattering and Faraday wave-based techniques that have enabled the development of phonon lasers, quantum computers and advanced vibration sensors. In particular, our discussion is centred around potential applications of AFCs in precision measurements in various physical, chemical and biological systems in conditions where using light, and hence optical FCs, faces technical and fundamental limitations, which is, for example, the case in underwater distance measurements and biomedical imaging applications. This review article will also be of interest to readers seeking a discussion of specific theoretical aspects of different classes of AFCs. To that end, we support the mainstream discussion by the results of our original analysis and numerical simulations that can be used to design the spectra of AFCs generated using oscillations of gas bubbles in liquids, vibrations of liquid drops and plasmonic enhancement of Brillouin light scattering in metal nanostructures. We also discuss the application of non-toxic room-temperature liquid-metal alloys in the field of AFC generation.

Magneto-Electronic Hydrogen Gas Sensors: A Critical Review

Devices enabling early detection of low concentrations of leaking hydrogen and precision measurements in a wide range of hydrogen concentrations in hydrogen storage systems are essential for the mass-production of fuel-cell vehicles and, more broadly, for the transition to the hydrogen economy. Whereas several competing sensor technologies are potentially suitable for this role, ultra-low fire-hazard, contactless and technically simple magneto-electronic sensors stand apart because they have been able to detect the presence of hydrogen gas in a range of hydrogen concentrations from 0.06% to 100% at atmospheric pressure with the response time approaching the industry gold standard of one second. This new kind of hydrogen sensors is the subject of this review article, where we inform academic physics, chemistry, material science and engineering communities as well as industry researchers about the recent developments in the field of magneto-electronic hydrogen sensors, including those based on magneto-optical Kerr effect, anomalous Hall effect and Ferromagnetic Resonance with a special focus on Ferromagnetic Resonance (FMR)-based devices. In particular, we present the physical foundations of magneto-electronic hydrogen sensors and we critically overview their advantages and disadvantages for applications in the vital areas of the safety of hydrogen-powered cars and hydrogen fuelling stations as well as hydrogen concentration meters, including those operating directly inside hydrogen-fuelled fuel cells. We believe that this review will be of interest to a broad readership, also facilitating the translation of research results into policy and practice.

Phase Change Metasurfaces by Continuous or Quasi-Continuous Atoms for Active Optoelectronic Integration

In recent decades, metasurfaces have emerged as an exotic and appealing group of nanophotonic devices for versatile wave regulation with deep subwavelength thickness facilitating compact integration. However, the ability to dynamically control the wave-matter interaction with external stimulus is highly desirable especially in such scenarios as integrated photonics and optoelectronics, since their performance in amplitude and phase control settle down once manufactured. Currently, available routes to construct active photonic devices include micro-electromechanical system (MEMS), semiconductors, liquid crystal, and phase change materials (PCMs)-integrated hybrid devices, etc. For the sake of compact integration and good compatibility with the mainstream complementary metal oxide semiconductor (CMOS) process for nanofabrication and device integration, the PCMs-based scheme stands out as a viable and promising candidate. Therefore, this review focuses on recent progresses on phase change metasurfaces with dynamic wave control (amplitude and phase or wavefront), and especially outlines those with continuous or quasi-continuous atoms in favor of optoelectronic integration.

All-dielectric magnetic metasurface for advanced light control in dual polarizations combined with high-Q resonances

Nanostructured magnetic materials provide an efficient tool for light manipulation on sub-nanosecond and sub-micron scales, and allow for the observation of the novel effects which are fundamentally impossible in smooth films. For many cases of practical importance, it is vital to observe the magneto-optical intensity modulation in a dual-polarization regime. However, the nanostructures reported on up to date usually utilize a transverse Kerr effect and thus provide light modulation only for p-polarized light. We present a concept of a transparent magnetic metasurface to solve this problem, and demonstrate a novel mechanism for magneto-optical modulation. A 2D array of bismuth-substituted iron-garnet nanopillars on an ultrathin iron-garnet slab forms a metasurface supporting quasi-waveguide mode excitation. In contrast to plasmonic structures, the all-dielectric magnetic metasurface is shown to exhibit much higher transparency and superior quality-factor resonances, followed by a multifold increase in light intensity modulation. The existence of a wide variety of excited mode types allows for advanced light control: transmittance of both p- and s-polarized illumination becomes sensitive to the medium magnetization, something that is fundamentally impossible in smooth magnetic films. The proposed metasurface is very promising for sensing, magnetometry and light modulation applications.

The authors fabricate and investigate the metasurface made of 2D iron-garnet subwavelength nanopillar array on a thin iron-garnet film. It exhibits high quality-factor resonances, leading to a multifold increase in light intensity modulation of the transmitted light with an advantage of P and S polarizations both sensitive to the medium magnetization.

Experimental observation of tunable Wood type resonances in an all-ferrodielectric periodical metasurface

In this Letter, a completely ferrodielectric metasurface consisting of an array of cylinders on a substrate is studied. All structural elements are made of ferrodielectric material. The conditions for the excitation of Wood's anomaly mode, obtained for different geometric parameters of the metasurface, are revealed. By continuously changing the structure parameters, we can change the position of the resonance at the Wood anomaly, thereby setting the position of the resonance at the frequency we need. It is shown that there is a resonant increase in the polarization plane rotation of the transmitted waves at the corresponding resonant frequency of the lattice mode excitation. Such polarization rotation is demonstrated both experimentally and theoretically.

Lab-On-Fiber Technology: A Roadmap toward Multifunctional Plug and Play Platforms

This review presents an overview of the “lab-on-fiber technology” vision and the main milestones set in the technological roadmap to achieve the ultimate objective of developing flexible, multifunctional plug and play fiber-optic platforms designed for specific applications. The main achievements, obtained with nanofabrication strategies for unconventional substrates, such as optical fibers, are discussed here. The perspectives and challenges that lie ahead are highlighted with a special focus on full spatial control at the nanoscale and high-throughput production scenarios. The rapid progress in the fabrication stage has opened new avenues toward the development of multifunctional plug and play platforms, discussed here with particular emphasis on new functionalities and unparalleled figures of merit, to demonstrate the potential of this powerful technology in many strategic application scenarios. The paper also analyses the benefits obtained from merging lab-on-fiber (LOF) technology objectives with the emerging field of optomechanics, especially at the microscale and the nanoscale. We illustrate the main advances at the fabrication level, describe the main achievements in terms of functionalities and performance, and highlight future directions and related milestones. All achievements reviewed and discussed clearly suggest that LOF technology is much more than a simple vision and could play a central role not only in scenarios related to diagnostics and monitoring but also in the Information and Communication Technology (ICT) field, where optical fibers have already yielded remarkable results.

Enhancement of Both Faraday and Kerr Effects with an All-Dielectric Grating Based on a Magneto-Optical Nanocomposite Material

We report on the design, fabrication, and characterization of an all-dielectric one-dimensional (1D) resonant device formed by a silicon nitride grating impregnated by a low-index magneto-optical silica-type matrix. This impregnation is realized through the dipping of the 966 nm periodic template in a sol-gel solution previously doped with CoFe₂O₄ nanoparticles, and able to fill the grating slits. By a proper adjustment of the geometrical parameters of such a photonic crystal membrane, simultaneous excitation of transverse electric (TE) and transverse magnetic (TM) polarization resonances is nearly achieved at 1570 nm. This TE/TM phase-matching situation leads to a fivefold enhancement of the Faraday effect in the resonance area with an increased merit factor of 0.32°. Moreover, the device demonstrates its ability to enhance longitudinal and transverse Kerr effects for the other directions of the applied magnetic field. Taking benefits from the ability of the nanocomposite material to be processed on photonic platforms, and despite its quite low magneto-optical activity compared to classical magnetic materials, this work proves that an all-dielectric 1D device can produce a high magneto-optical sensitivity to every magnetic field directions.

Surface Plasmon Resonance (SPR) to Magneto-Optic SPR

In this editorial, a brief background of the surface plasmon resonance (SPR) principle is discussed, followed by several aspects of magneto-optic SPR (MOSPR) and sensing schemes from the viewpoint of fundamental studies and potential technological applications. New sensitivity metrics are introduced that would allow researchers to compare the performance of SPR and MOSPR-based sensors. Merits of MOSPR over SPR based sensors and challenges faced by MOSPR sensors in terms of their practical use and portability are also considered. The editorial ends with potential new configurations and future prospects. This work is considered highly significant to device engineers, graduate and undergraduate students, and researchers of all levels involved in developing new classes of bio-devices for sensing, imaging, environmental monitoring, toxic gas detection, and surveying applications to name a few.

UV plasmonic properties of colloidal liquid-metal eutectic gallium-indium alloy nanoparticles

Nanoparticles made of non-noble metals such as gallium have recently attracted significant attention due to promising applications in UV plasmonics. To date, experiments have mostly focused on solid and liquid pure gallium particles immobilized on solid substrates. However, for many applications, colloidal liquid-metal nanoparticle solutions are vital. Here, we experimentally demonstrate strong UV plasmonic resonances of eutectic gallium-indium (EGaIn) liquid-metal alloy nanoparticles suspended in ethanol. We rationalise experimental results through a theoretical model based on Mie theory. Our results contribute to the understanding of UV plasmon resonances in colloidal liquid-metal EGaIn nanoparticle suspensions. They will also enable further research into emerging applications of UV plasmonics in biomedical imaging, sensing, stretchable electronics, photoacoustics, and electrochemistry.

Resonant spin wave excitation in magnetoplasmonic bilayers using short laser pulses

In magnetically ordered solids a static magnetic field can be generated by virtue of the transverse magneto-optical Kerr effect (TMOKE). Moreover, the latter was shown to be dramatically enhanced due to the optical excitation of surface plasmons in nanostructures with relatively small optical losses. In this paper we suggest a new method for resonant optical excitation in a prototypical bilayer composed of a noble metal (Au) with grating and a ferromagnetic thin film of yttrium iron garnet (YIG) via a frequency comb. Based on magnetization dynamics simulations we show that for a frequency comb with certain parameters, chosen to be resonant with the spin-wave excitations of YIG, the TMOKE is drastically enhanced, hinting at possible technological applications in optical control of spintronics systems.

Nonreciprocal hybrid magnetoplasmonics

The Faraday effect describes the phenomenon that a magnetized material can alter the polarization state of transmitted light. Interestingly, unlike most light-matter interactions in nature, it breaks Lorentz reciprocity. This exceptional behavior is utilized for applications such as optical isolators, which are core elements in communication and laser systems. While there is high demand for sub-micron nonreciprocal photonic devices, the realization of such systems is extremely challenging as conventional magneto-optic materials only provide weak magneto-optic response within small volumes. Plasmonics could be a key to overcome this hurdle in the future: over the last years there have been several lines of work demonstrating that different types of metallic nanostrutures can be utilized to greatly enhance the magneto-optic response of conventional materials. In this review we give an overview over the state of the art in the field and highlight recent developments on hybrid plasmonic Faraday rotators. Our discussions are mainly focused on the visible and near-infrared wavelength regions and cover both experimental realizations as well as analytical descriptions. Special attention will be paid to recent developments on hybrid plasmonic thin film systems consisting of gold and europium chalcogenides.

Giant enhancement of Faraday rotation due to electromagnetically induced transparency in all-dielectric magneto-optical metasurfaces

In this Letter we introduce a new class of Fano-resonant all-dielectric metasurfaces for enhanced, high figure of merit magneto-optical response. The metasurfaces are formed by an array of magneto-optical bismuth-substituted yttrium iron garnet nano-disks embedded into a low-index matrix. The strong field enhancement in the magneto-optical disks, which results in over an order of magnitude enhancement of Faraday rotation, is achieved by engineering two (electric and magnetic) resonances. It is shown that while enhancement of rotation also takes place for spectrally detuned resonances, the resonant excitation inevitably results in stronger reflection and low figure of merit of the device. We demonstrate that this can be circumvented by overlapping electric and magnetic resonances of the nanodisks, yielding a sharp electromagnetically induced transparency peak in the transmission spectrum, which is accompanied by gigantic Faraday rotation. Our results show that one can simultaneously obtain a large Faraday rotation enhancement along with almost 100% transmittance in an all-dielectric metasurface as thin as 300 nm. A simple analytical model based on coupled-mode theory is introduced to explain the effects observed in first-principle finite element method simulations.

Electric-current-induced unidirectional propagation of surface plasmon-polaritons

Nonreciprocity and one-way propagation of optical signals are crucial for modern nanophotonic technology, and typically achieved using magneto-optical effects requiring large magnetic biases. Here we suggest a fundamentally novel approach to achieve unidirectional propagation of surface plasmon-polaritons (SPPs) at metal-dielectric interfaces. We employ a direct electric current in metals, which produces a Doppler frequency shift of SPPs due to the uniform drift of electrons. This tilts the SPP dispersion, enabling one-way propagation, as well as zero and negative group velocities. The results are demonstrated for planar interfaces and cylindrical nanowire waveguides.

Preparation of High Mechanical Performance Nano-Fe₃O₄/Wood Fiber Binderless Composite Boards for Electromagnetic Absorption via a Facile and Green Method

Fe₃O₄/wood fiber composites are prepared with a green mechanical method using only distilled water as a solvent without any chemical agents, and then a binderless composite board with high mechanical properties is obtained via a hot-press for electromagnetic (EM) absorption. The fibers are connected by hydrogen bonds after being mechanically pretreated, and Fe₃O₄ nanoparticles (NPs) are attached to the fiber surface through physical adsorption. The composite board is bonded by an adhesive, which is provided by the reaction of fiber composition under high temperature and pressure. The Nano-Fe₃O₄/Fiber (NFF) binderless composite board shows remarkable microwave absorption properties and high mechanical strength. The optional reflection loss (RL) of the as-prepared binderless composite board is -31.90 dB. The bending strength of the NFF binderless composite board is 36.36 MPa with the addition of 6% nano-Fe₃O₄, the modulus of elasticity (MOE) is 6842.16 MPa, and the internal bond (IB) strength is 0.81 MPa. These results demonstrate that magnetic nanoparticles are deposited in binderless composite board by hot pressing, which is the easiest way to produce high mechanical strength and EM absorbers.

Tunable Magneto-Optical Kerr Effects of Nanoporous Thin Films

Magnetoplasmonics, combining magnetic and plasmonic functions, has attracted increasing attention owing to its unique magnetic and optical properties in various nano-architectures. In this work, Ag, CoFeB and ITO layers are fabricated on anodic aluminum oxide (AAO) porous films to form hybrid multi-layered nanoporous thin films by magnetron sputtering deposition process. The designed nanostructure supports localized surface plasmon resonance (LSPR) and tunable magneto-optical (MO) activity, namely, the sign inversion, which can be controlled by AAO porous film geometry (pore diameter and inter-pore spacing) flexibly. The physical mechanism of this special MO phenomena is further analyzed and discussed by the correlation of Kerr rotation and electronic oscillations controlled by the surface plasmon resonance that is related to the nanoporous structure.

Strong Magneto-Optical Response of Nonmagnetic Organic Materials Coupled to Plasmonic Nanostructures

Plasmonic nanoparticles (PNPs) can significantly modify the optical properties of nearby organic molecules and thus present an attractive opportunity for sensing applications. However, the utilization of PNPs in conventional absorption, fluorescence, or Raman spectroscopy techniques is often ineffective due to strong absorption background and light scattering, particularly in the case of turbid solutions, cell suspensions, and biological tissues. Here we show that nonmagnetic organic molecules may exhibit magneto-optical response due to binding to a PNP. Specifically, we detect strong magnetic circular dichroism signal from supramolecular J-aggregates, a representative organic dye, upon binding to silver-coated gold nanorods. We explain this effect by strong coupling between the J-aggregate exciton and the nanoparticle plasmon, leading to the formation of a hybrid state in which the exciton effectively acquires magnetic properties from the plasmon. Our findings are fully corroborated by theoretical modeling and constitute a novel magnetic method for chemo- and biosensing, which (upon adequate PNP functionalization) is intrinsically insensitive to the organic background and thus offers a significant advantage over conventional spectroscopy techniques.

Magneto-Optical Response of Cobalt Interacting with Plasmonic Nanoparticle Superlattices

The magneto-optical Kerr effect is a striking phenomenon whereby the optical properties of a material change under an applied magnetic field. Though promising for sensing and data storage technology, these properties are typically weak in magnitude and are inherently limited by the bulk properties of the active magnetic material. In this work, we theoretically demonstrate that plasmonic thin-film assemblies on a cobalt substrate can achieve tunable transverse magneto-optical (TMOKE) responses throughout the visible and near-infrared (300-900 nm). In addition to exhibiting wide spectral tunability, this response can be varied in sign and magnitude by changing the plasmonic volume fraction (1-20%), the composition and arrangement of the assembly, and the shape of the nanoparticle inclusions. Of particular interest is the newly discovered sensitivity of the sign and intensity of the TMOKE spectrum to collective metallic plasmonic behavior in silver, mixed silver-gold, and anisotropic superlattices.

Plasmonic nanoantenna hydrophones

Ultrasound is a valuable biomedical imaging modality and diagnostic tool. Here we theoretically demonstrate that a single dipole plasmonic nanoantenna can be used as an optical hydrophone for MHz-range ultrasound. The nanoantenna is tuned to operate on a high-order plasmon mode, which provides an increased sensitivity to ultrasound in contrast to the usual approach of using the fundamental dipolar plasmon resonance. Plasmonic nanoantenna hydrophones may be useful for ultrasonic imaging of biological cells, cancer tissues or small blood vessels, as well as for Brillouin spectroscopy at the nanoscale.

Anisotropic Nanoantenna-Based Magnetoplasmonic Crystals for Highly Enhanced and Tunable Magneto-Optical Activity

We present a novel concept of a magnetically tunable plasmonic crystal based on the excitation of Fano lattice surface modes in periodic arrays of magnetic and optically anisotropic nanoantennas. We show how coherent diffractive far-field coupling between elliptical nickel nanoantennas is governed by the two in-plane, orthogonal and spectrally detuned plasmonic responses of the individual building block, one directly induced by the incident radiation and the other induced by the application of an external magnetic field. The consequent excitation of magnetic field-induced Fano lattice surface modes leads to highly tunable and amplified magneto-optical effects as compared to a continuous film or metasurfaces made of disordered noninteracting magnetoplasmonic anisotropic nanoantennas. The concepts presented here can be exploited to design novel magnetoplasmonic sensors based on coupled localized plasmonic resonances, and nanoscale metamaterials for precise control and magnetically driven tunability of light polarization states.