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The study of spin–orbit coupling (SOC) of light is crucial to explore the light–matter interactions in sub-wavelength structures. By designing a plasmonic lattice with chiral configuration that provides parallel angular momentum and spin components, one can trigger the strength of the SOC phenomena in photonic or plasmonic crystals. Herein, we explore the SOC in a plasmonic crystal, both theoretically and experimentally. Cathodoluminescence (CL) spectroscopy combined with the numerically calculated photonic band structure reveals an energy band splitting that is ascribed to the peculiar spin–orbit interaction of light in the proposed plasmonic crystal. Moreover, we exploit angle-resolved CL and dark-field polarimetry to demonstrate circular-polarization-dependent scattering of surface plasmon waves interacting with the plasmonic crystal. This further confirms that the scattering direction of a given polarization is determined by the transverse spin angular momentum inherently carried by the SP wave, which is in turn locked to the direction of SP propagation. We further propose an interaction Hamiltonian based on axion electrodynamics that underpins the degeneracy breaking of the surface plasmons due to the spin–orbit interaction of light. Our study gives insight into the design of novel plasmonic devices with polarization-dependent directionality of the Bloch plasmons. We expect spin–orbit interactions in plasmonics will find much more scientific interests and potential applications with the continuous development of nanofabrication methodologies and uncovering new aspects of spin–orbit interactions.

Correlative electron-photon spectroscopy without a laser The multidisciplinary ERC Starting Grant project “Quantum Coherent Control: Self-Interference of Electron Beams with Nanostructures (NanoBeam)” combines experiments and simulations to develop scanning electron microscopes into a practical tool for probing electron dynamics at the nanoscale, opening new vistas for nanotechnology and materials science.

Nature physics 19(6), 869 - 876 (2023). doi:10.1038/s41567-023-01954-3, Ultrafast photon–electron spectroscopy in electron microscopes commonly requires ultrafast laser setups. Photoemission from an engineered electron source is used to generate pulsed electrons, interacting with a sample excited by the laser pulse at a known time delay. Thus, developing an ultrafast electron microscope demands the exploitation of extrinsic laser excitations and complex synchronization schemes. Here we present an inverse approach to introduce internal radiation sources in an electron microscope based on cathodoluminescence spectroscopy. Our compact method is based on a sequential interaction of the electron beam with an electron-driven photon source and the investigated sample. Such a source in an electron microscope generates phase-locked photons that are mutually coherent with the near-field distribution of the swift electron. We confirm the mutual frequency and momentum-dependent correlation of the electron-driven photon source and sample radiation and determine a degree of mutual coherence of up to 27%. With this level of mutual coherence, we were able to perform spectral interferometry with an electron microscope. Our method has the advantage of being simple, compact and operating with continuous electron beams. It will open the door to local photon–electron correlation spectroscopy of quantum materials, single-photon systems and coherent exciton–polaritonic samples with nanometre resolution., Published by Nature Publishing Group, Basingstoke

Increasing body mass index can have negative effects on employees' ability to work and increase the risk of accidents and occupational injuries and the risk of death. The aim of this study was to examine the effect of 12 week a selected aerobic exercise program on body composition, lipid profile, and working ability of employees involved overweight and obese. In this semi-experimental study with pre-test, post-test design and control group, 65 overweight employees were selected by purposive sampling method and randomly assigned to exercise and control groups. Then aerobic exercise program three sessions per week and each session 65-50 minutes, was performed for 12 weeks for the experimental group. The control group did not have such an intervention. Body composition indices, workability index and, lipid profile were measured before and after the training protocol for both groups. Data were analyzed using the covariance test (ANCOVA). The results showed that aerobic exercise significantly reduced body composition indices, including (fat percentage, body mass index, waist to pelvic ratio) and total cholesterol, triglyceride, low-density lipoprotein (LDL) the exercise group compared with the control group. The levels of high-density lipoprotein (HDL) and the ability to work index of the exercise group also increased (P

Electron beams in electron microscopes are efficient probes of optical near-fields, thanks to spectroscopy tools like electron energy-loss spectroscopy and cathodoluminescence spectroscopy. Nowadays, we can acquire multitudes of information about nanophotonic systems by applying space-resolved diffraction and time-resolved spectroscopy techniques. In addition, moving electrons interacting with metallic materials and optical gratings appear as coherent sources of radiation. A swift electron traversing metallic nanostructures induces polarization density waves in the form of electronic collective excitations, i.e., the so-called plasmon polariton. Propagating plasmon polariton waves normally do not contribute to the radiation; nevertheless, they diffract from natural and engineered defects and cause radiation. Additionally, electrons can emit coherent light waves due to transition radiation, diffraction radiation, and Smith-Purcell radiation. Some of the mechanisms of radiation from electron beams have so far been employed for designing tunable radiation sources, particularly in those energy ranges not easily accessible by the state-of-the-art laser technology, such as the THz regime. Here, we review various approaches for the design of coherent electron-driven photon sources. In particular, we introduce the theory and nanofabrication techniques and discuss the possibilities for designing and realizing electron-driven photon sources for on-demand radiation beam shaping in an ultrabroadband spectral range to be able to realize ultrafast few-photon sources. We also discuss our recent attempts for generating structured light from precisely fabricated nanostructures. Our outlook for the realization of a correlative electron-photon microscope/spectroscope, which utilizes the above-mentioned radiation sources, is also described.

Inelastic interaction of free-electrons with optical near fields has recently attracted attention for manipulating and shaping free-electron wavepackets. Understanding the nature and the dependence of the inelastic cross section on the polarization of the optical near-field is important for both fundamental aspects and the development of new applications in quantum-sensitive measurements. Here, we investigate the effect of the polarization and the spatial profile of plasmonic near-field distributions on shaping free-electrons and controlling the energy transfer mechanisms, but also tailoring the electron recoil. We particularly show that polarization of the exciting light can be used as a control knop for disseminating the acceleration and deceleration path ways via the experienced electron recoil. We also demonstrate the possibility of tailoring the shape of the localized plasmons by incorporating specific arrangements of nanorods to enhance or hamper the transversal and longitudinal recoils of free-electrons. Our findings open up a route towards plasmonic near-fields-engineering for the coherent manipulation and control of slow electron beams for creating desired shapes of electron wavepackets.

ACS photonics 9(7), 2473 - 2482 (2022). doi:10.1021/acsphotonics.2c00586, Transition-metal dichalcogenides with their exciton-dominated optical behavior emerge as promising materials for realizing strong light–matter interactions in the visible range and at ambient conditions. When these materials are combined with metals, the energy confining ability of plasmon polaritons in metals below the diffraction limit allows for further enhancing and tailoring the light–matter interaction due to the formation of plexcitons in hybrid metal-TMDC structures at the interface. Herein, we demonstrate that the coupling between quasi-propagating plasmons in plasmonic crystals and excitons in WSe2 provides a multioscillator playground for tailoring the band structure of plasmonic crystal structures and results in emerging flat bands. The cathodoluminescence spectroscopy and angle-resolved measurements combined with the numerically calculated photonic band structure confirm a strong exciton–plasmon coupling, leading to significant changes in the band diagram of the hybrid lattice and the ability to tailor the band diagram via strong coupling. The hybrid plexcitonic crystal structures investigated here sustain optical waves with remarkably low group velocities. These results could be used for designing tunable slow-light structures based on the strong coupling effect and pave the way for plexcitonic topological photonic structures., Published by ACS, Washington, DC

Relativistic electron beams create optical radiation when interacting with tailored nanostructures. This phenomenon has been so far used to design grating-based and holographic electron-driven photon sources. It has been proposed recently that such sources can be used for hybrid electron- and light-based spectroscopy techniques. However, this demands the design of a thin-film source suitable for electron-microscopy applications. Here, we present a mesoscopic structure composed of an array of nanoscale holes in a gold film which is designed using transformation optics and delivers ultrashort chirped electromagnetic wave packets upon 30–200 keV electron irradiation. The femtosecond photon bunches result from coherent scattering of surface plasmon polaritons with hyperbolic dispersion. They decay by radiation in a broad spectral band which is focused into a 1.5 micrometer beam waist. The focusing ability and broadband nature of this photon source will initiate applications in ultrafast spectral interferometry techniques., There is growing interest in designing platforms for coherent electron-driven photon sources for hybrid light and electron spectroscopy. Here the authors demonstrate generation of coherent broadband ultrashort light pulses upon electron irradiation to nanostructured gold plated film.

Pre-diabetes is defined as an increase in blood glucose levels above normal, but not to the extent that it is considered diabetes. One way to control the progression of diabetes is to eat a healthy diet and exercise. Accordingly, the aim of this study was to investigate the effect of combined exercise and coffee consumption on fasting blood sugar and middle-aged pre diabetic men. In this study, 44 overweight middle-aged men with (body mass index of 28.3 ± 2.8 kg / m2) were purposefully selected and randomly divided into four groups of 11: Exercise Combination, coffee consumption, combined exercise + coffee consumption and control group were divided. Pre-test and post-test groups including weight, body mass index, percentage of fasting fat and blood glucose were measured 24 hours before and after the project. The training groups then performed the training protocol for 8 weeks, three sessions per minute and 90 minutes each session. The coffee and exercise + coffee group consumed 10 grams of coffee every other day. Data were analyzed using covariance test and significance level of 0.05. The results showed a significant decrease in body mass index, fat percentage and serum concentration of fasting blood glucose in the exercise groups compared to the control group (P> 5%). This study showed that combined exercise with coffee can be effective in controlling fasting blood sugar and abdominal obesity.

Dipole selection rules underpin much of our understanding in characterization of matter and its interaction with external radiation. However, there are several examples where these selection rules simply break down, for which a more sophisticated knowledge of matter becomes necessary. An example, which is increasingly becoming more fascinating, is macroscopic toroidization (density of toroidal dipoles), which is a direct consequence of retardation. In fact, dissimilar to the classical family of electric and magnetic multipoles, which are outcomes of the Taylor expansion of the electromagnetic potentials and sources, toroidal dipoles are obtained by the decomposition of the moment tensors. This review aims to discuss the fundamental and practical aspects of the toroidal multipolar moments in electrodynamics, from its emergence in the expansion set and the electromagnetic field associated with it, the unique characteristics of their interaction with external radiations and other moments, to the recent attempts to realize pronounced toroidal resonances in smart configurations of meta-molecules. Toroidal moments not only exhibit unique features in theory but also have promising technologically relevant applications, such as data storage, electromagnetic-induced transparency, unique magnetic responses and dichroism.

We study the interaction of swift electrons with laser and solids using a numerical approach, and specifically show that low-energy electrons can be used to map the time-resolved response of a Fermi gas.

International audience; Dynamic toroidal dipoles, a distinguished class of fundamental electromagnetic sources, receive increasing interest and participate in fascinating electrodynamic phenomena and sensing applications. As described in the literature, the radiative nature of dynamic toroidal dipoles is sometimes confounded, intermixing with static toroidal dipoles and plasmonic dark modes. Here, we elucidate this issue and provide proof-of-principle experiments exclusively on the radiation behavior of dynamic toroidal moments. Optical toroidal modes in plasmonic heptamer nanocavities are analyzed by electron energy loss spectroscopy and energy-filtered transmission electron microscopy supported by finite-difference time-domain numerical calculations. Additionally, their corresponding radiation behaviors are experimentally investigated by means of cathodoluminescence. The observed contrasting behaviors of a single dynamic toroidal dipole mode and an antiparallel toroidal dipole pair mode are discussed and elucidated. Our findings further clarify the electromagnetic properties of dynamic toroidal dipoles and serve as important guidance for the use of toroidal dipole moments in future applications.

In this chapter, criteria for existence of propagating optical modes which are transversely bound at the interface of two materials are studied. In particular, quite general cases are considered, where the materials involved are assumed to be anisotropic, but also demonstrating magneto-electric effects. Moreover, surface states of two-dimensional materials like topological insulators and graphene are also modeled via consideration of a conductivity sheet existing at the interface. A characteristic equation for obtaining the propagation constant of generalized interface modes is presented. Furthermore, optical modes sustained by a thin film of anisotropic materials with magneto-electric effect and topological surface states are also investigated. It is shown that interface modes supported by such a system are hybrid in nature, and can be further decomposed into the well-known classes of transverse magnetic and electric modes, only at the absence of magneto-electric effect. Although the formulations driven here are mathematically abstract, they can be used to investigate polaritons in van der Waal materials, hyperbolic materials, and topological insulators.

Toroidal moments have recently attracted attentions as an individual class of moments, by expanding the vector potential and decomposing the third component into toroidal moments and magnetic quadrupoles. Toroidal moments sustain peculiar time-space symmetry relations and are known as hybrid modes, which can be only understood by including retardation effects. Here, we outline our recent attempts to realize toroidal moments in void oligomeric meta-molecules. These structures are investigated experimentally using electron energy-loss spectroscopy and numerically using finite-difference time-domain method. We discuss about various toroidal moments supported by these structures, the role of symmetry and topology in excitation of these moments, the radiation from electron-induced toroidal moments resolved by cathodoluminescence spectroscopy, and finally hybridization of toroidal moments in coupled oligomers. Our findings outline the necessity of including toroidal moments within the classes of electromagnetic moments, despite the current discrepancy about their significance.

The motion of nanomotors triggered by light sources will provide new alternative routes to power nanoarchitectures without the need of chemical fuels. However, most light-driven nanomotors are triggered by UV-light, near infrared reflection, or laser sources. It is demonstrated that nanocap shaped Au/TiO2 nanomotors (175 nm in diameter) display increased Brownian motion in the presence of broad spectrum visible light. The motion results from the surface plasmon resonance effect leading to self-electrophoresis between the Au and TiO2 layers, a mechanism called plasmonic photocatalytic effect in the field of photocatalysis. This mechanism is experimentally characterized by electron energy loss spectroscopy, energy-filtered transmission electron microscopy, and optical video tracking. This mechanism is also studied in a more theoretical manner using numerical finite-difference time-domain simulations. The ability to power nanomaterials with visible light may result in entirely new applications for externally powered micro/nanomotors.

Investigating the interaction of electron beams with materials and light has been a field of research since more than a century. The field was advanced theoretically by the raise of quantum mechanics and technically by the introduction of electron microscopes and accelerators. It is possible nowadays to uncover a multitude of information from electron-induced excitations in matter by means of advanced techniques like holography, tomography, and most recently photon-induced near-field electron microscopy. The question is whether the interaction can be controlled in an even more efficient way in order to unravel important questions like modal decomposition of the electron-induced polarization, by performing experiments with better spatial, temporal, and energy resolutions. This review discusses recent advances in controlling the electron and light interactions at the nanoscale. Theoretical and numerical aspects of the interaction of electrons with nanostructures and metamaterials will be discussed, with the aim to understand mechanisms of radiation in interaction of electrons with even more sophisticated structures., 38 pages, 14 Figures

Interference patterns are not only a defining characteristic of waves, but also have several applications; characterization of coherent processes and holography. Spatial holography with electron waves, has paved the way towards space-resolved characterization of magnetic domains and electrostatic potentials with angstrom spatial resolution. Another impetus in electron microscopy has been introduced by ultrafast electron microscopy which uses pulses of sub-picosecond durations for probing a laser induced excitation of the sample. However, attosecond temporal resolution has not yet been reported, merely due to the statistical distribution of arrival times of electrons at the sample, with respect to the laser time reference. This is however, the very time resolution which will be needed for performing time-frequency analysis. These difficulties are addressed here by proposing a new methodology to improve the synchronization between electron and optical excitations through introducing an efficient electron-driven photon source. We use focused transition radiation of the electron as a pump for the sample. Due to the nature of transition radiation, the process is coherent. This technique allows us to perform spectral interferometry with electron microscopes, with applications in retrieving the phase of electron-induced polarizations and reconstructing dynamics of the induced vector potential.

We present a comprehensive theoretical and experimental investigation of the plasmon hybridization of coupled split-ring resonators by means of the electron energy-loss spectroscopy. Split-ring resonator is a key element in design of negative refractive index metamaterials, and has been therefore intensively studied in the literature. Here, our aim is the study of hybridization effects for higher-order non-dipolar modes, which have been not investigated beforehand. We provide a complete scheme of the multimodal distribution of the coupled and single-element split-ring resonators, with a precise attention to the hybridization of those modes according to the induced moments. Our study suggests a clear dominance of electric and magnetic dipole moments over higher-order modes in the far-field radiation spectrum.

Hyperbolic media exhibit unparalleld properties, e.g, as light absorbers in photovoltaics and photonics, as superlenses in far-field imaging, as subwavelength light concentrators in nanolithography, or as novel materials in emission engineering. With the advent of optical metamaterials, deliberate design of material properties became possible. However, inadvertent variability in fabrication techniques and other factors limit performance characteristics of man-made hyperbolic materials. Here, we draw attention to a class of natural hyperbolic materials, the tetradymites. From generalized spectroscopic ellipsometry we extract the dielectric tensor components and find hyperbolic behavior in Bi_2Se_3 and Bi_2Te_3 in the near-infrared to visible spectrum. Previously, natural hyperbolic media were known only in the far-infrared spectral range. As possible applications of tetradymites we discuss superlenses for near-field microscopy and far-field isoindex filters. Solid solutions of tetradymites are likely tunable in operational wavelength from the infrared to the visible, complementing hyperbolic metamaterials.

The investigation of surface plasmon excitations has recently become a field of research due to their high potential to be applicable in sensors, information technologies, cancer research etc. These coherent delocalized electron oscillations are common at metal-dielectric interfaces. However, they also exist in highly doped semiconductors, conducting oxide system or graphene, i.e. in many other systems with high carrier mobility. This poses the question whether such resonances can also be observed at the insulator interfaces.

In this paper, we present a systematic investigation of symmetry-breaking in the plasmonic modes of triangular gold nanoprisms. Their geometrical C(3v) symmetry is one of the simplest possible that allows degeneracy in the particle's mode spectrum. It is reduced to the nondegenerate symmetries C(v) or E by positioning additional, smaller gold nanoprisms in close proximity, either in a lateral or a vertical configuration. Corresponding to the lower symmetry of the system, its eigenmodes also feature lower symmetries (C(v)), or preserve only the identity (E) as symmetry. We discuss how breaking the symmetry of the plasmonic system not only breaks the degeneracy of some lower order modes, but also how it alters the damping and eigenenergies of the observed Fano-type resonances.

Background: The most important cause of kidney injury is renal ischemia/reperfusion injury (IRI), which is gender-related. This study was designed to investigate the protective role of Γ-aminobutyric acid (GABA (against IRI in male and female rats. Materials and Methods: Thirty-six female and male wistar rats were assigned to six experimental groups. The IRI was induced by clamping renal vessels for 45 min then was performed reperfusion for 24 h. The group sex posed to IRI were pretreated with GABA and were compared with the control groups. Results: Serum levels of creatinine and blood urea nitrogen, kidney weight, and kidney tissue damage score increased in the IRI alone groups, (P < 0.05), while GABA decreased these parameters in female significantly (P < 0.05), but not in male rats. Uterus weight decreased significantly in female rats treated with GABA. Testis weight did not alter in male rats. Serum level of nitrite and kidney level of malondialdehyde (MDA) had no significant change in both female and male rats. Kidney level of nitrite increased significantly in female rats experienced IRI and serum level of MDA increased significantly in males that were exposed to IRI (P < 0.05). Conclusion: GABA could ameliorate kidney injury induced by renal IRI in a gender dependent manner.

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

The paper introduces a wavelength converter composed of a metallic finite 2-dimensional particle grating on top of an optical waveguide. The particles sustain plasmonic resonances which will result in the near-field enhancement and therefore, high conversion efficiency. Due to near-field interaction of the grating field with the propagating modes of the waveguide, the generated third harmonic wave is phase-matched to a propagating mode of the waveguide, while the fundamental frequency component is not coupled into the output waveguide of the structure. The performance of this structure is numerically investigated using a full-wave transmission line method for the linear analysis and a three-dimensional finite-difference time-domain method for the nonlinear analysis.