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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.

Cherenkov radiation is studied analytically in a dispersive bianisotropic medium with magnetoelectric effect. This study is based on the vector-potential approach. Notable features such as double cones of Cherenkov radiation in magnetoelectric media are studied and the angle of propagation cones are calculated, which allow for characterizing magnetoelectric materials. We also analyze emitted electromagnetic fields in the spectral domain to obtain radiated power and momentum-resolved electron energy-loss spectra. The impact of magnetoelectric coefficients on characteristics of the Cherenkov radiation is also investigated in order to introduce parameters for the characterization of magnetoelectric materials.

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.

In recent years, light with orbital angular momentum, or the so-called vortex beams, has been the subject of intense research, due to its applications in microscopy, telecommunications, and investigating the selection rules. Many efforts have been devoted to generate vortex beams using metasurfaces and metamaterials. However, most of them lack key properties in controlling the polarization, directionality and intensity of the light which is generated and directed from a localized radiation sources such as electron-beam induced emission. Recently, a photon-sieve structure has been designed, developed and characterized as an electron-driven photon source, which is formed by specific ordering of nanoholes in different sizes and lattices forming a helical arm in a thin layer of gold. Electron beams in a scanning electron microscope interacts with the surface of a photon-sieve structure acting as a broadband source of optical excitation. Both Chain plasmons and chiral surface plasmons are excited in this structure resulting in vortex beams propagating in vacuum. Here, we design a photon sieve structure that can generate vortex pairs, i.e., optical beams with entangled phase singularities of opposite signs associated with the topological charges. This phenomenon is experimentally studied utilizing a cathodoluminescence detector facilitated with angle-resolved mapping, polarimetry, and spectroscopy methods. Data obtained from the polarimeter suggests that the rotating behaviour of the vortices are caused by their orbital angular momentum rather than the polarization. Experimental data are further confirmed by numerical simulations suggesting that the interference between the propagating polaritons and reflection from the void ring is the main reason for observing counter propagating plasmons with opposite chirality in experimental images. We anticipate that this work presents a systematic method towards designing new generation of metasurfaces with the possibility to control directivity, angular momentum, and energy of the light beams.

Point-projection microscopy (PPM) with low energy electrons is developing into a powerful tool for holographic reconstruction of individual proteins and solid state nanostructures. In combination with laser-based photoemission schemes, it offers the exciting prospect of ultrafast coherent electron holography of single nanostructures. Such experiments would greatly benefit from a freestanding electron source with femtosecond time resolution, few-nm emitter size, and good coherence properties. Here, we use plasmonic nanofocusing on a conical gold taper and multiphoton photoemission from the taper apex to create such a source. It is implemented in a PPM setup and used to record in-line holograms of thin bundles of single-walled carbon nanotubes, demonstrating an effective emitter radius of less than 5 nm. We show that the same concept can also be transferred to tungsten tips, offering further improvements in emitter size and brightness. Numerical simulations show that such an ultrafast, low-energy electron s...

Dynamic toroidal multipoles are the third independent family of elementary electromagnetic sources in addition to electric and magnetic multipoles. Whereas the dipole–dipole coupling in electric and magnetic multipole families has been well studied, such fundamental coupling effects in the toroidal multipole family have not yet been experimentally investigated. Here we propose a plasmonic decamer nanocavity structure to realize transverse coupling between magnetic toroidal dipoles. The coupling effect was investigated both experimentally and theoretically, by means of electron energy-loss spectroscopy and energy-filtered transmission electron microscopy, together with finite-difference time-domain calculations. We observe that the coupling causes a reorientation of the magnetic moment loops surrounding the initial toroidal moments. This coupling results in three eigenstates of this toroidal system. The underlying coupling mechanism is qualitatively demonstrated. Our investigations pave the way toward a be...

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.

Photon induced near-field electron microscopy has been recently introduced to investigate the dynamics of near-field distributions in nanostructures, with femtosecond time and angstrom spatial resolution [1]. In this technique a laser beam excites both a photoemission electron gun and the sample inside an electron microscope chamber. The electron beams then probe the laser-induced excitations. Achieving attosecond temporal resolution to probe electron dynamics is however challenging, due to the requirement for a perfect synchronization between the electron waves and laser light. Recently an alternative approach based on cathodoluminescence (CL) has been proposed [2]. In this way, the interaction of swift electrons with a precisely designed electron-driven photon source (EDPHS) causes radiation of ultrashort optical pulses, which are focused onto the sample (Fig. 1a). The sample interacts with both the EDPHS radiation and the electron. The overall CL emission is controlled by the distance between the sample and the EDPHS. The distance-energy correlation map between the CL radiations from both the sample and EDPHS is then recorded and used to recover the spectral phase and time-resolved responses of the sample [3, 4] (Fig. 1b).

Interaction of a moving electron wave packet in free space with light and nanostructures have taken much attention recently, by the emergence of photon-induced near-field electron microscopy [1–2]. Electron beams can inelastically interact by laser-induced nearfield distribution of the nanostructures, opening ways in shaping the electron wave packets and characterization of plasmon polaritons. The interaction of high energy electron waves with laser-induced excitations in the sample is generally discussed within eikonal approximations, neglecting other effects which arise from the pondermotive forces and experienced elastic recoils [3–4]. In contrast, coherent control of above threshold ionization and high harmonic generation can be understood by interferences between different quantum paths, related to ponderomotive and absorptive parts in the minimal coupling Hamiltonian [5].

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.

EELS and CL have been introduced as efficient tools for probing nanooptical excitations in single nanostructures, with a nanometre spatial resolution and meV energy resolution. Thanks to the ultrafast interaction of localized relativistic electrons with the optical modes of nanostructures in TEMs, electron beams appear as an ultra-broadband probe of sample resonances. The inelastic interaction of a swift electron with nanostructures can be understood using a useful classical approach, as discussed in the previous chapter, that has been proven to be identical to the quantum-mechanical treatment when averaging over electron impact parameters weighted by the spot intensity (Ritchie and Howie in Philos Mag A 58(5):753–767, 1988 [3]).

Investigation of nanooptical systems by means of far-field optics suffers from the diffraction limit of light; hence, spatial resolutions beyond the optical wavelengths are hardly achievable. Many different approaches are employed to improve the spatial resolution. These methods have been shortly described in Chap. 1. Here, we briefly discuss in more details SNOM and PEEM, with the emphasis on the applicability of these methods to different optical systems and their advantages and limitations. EELS and CL will be more intensively described in the subsequent chapters.

Swift electrons can undergo inelastic interactions with single electrons as well as collective electron excitations within the sample, such as plasmon and phonon polaritons, as a result of which they lose energy (Garcia de Abajo in Rev. Mod. Phys. 82:209–275, 2010 [1]). Within the classical formalism, EEL spectra are theoretically rationalized by a simple but intuitive interpretation that has a direct correspondence with first principles, demanding that all inelastic signals are collected (Ritchie and Howie, in Philos. Mag. A 58:753–767, 1988 [2].

Combining laser and electron guns in electron microscopes has created a plethora of opportunities for characterizing the chemical reactions and near-field distributions of nanostructures (Park et al. in New J Phys 12:123028, 2010 [1]; Siwick et al. in Science 302:1382–1385, 2003 [2]; Barwick et al. in Nature 462:902–906, 2009 [3]; Zewail and Thomas in 4D electron microscopy, imaging in space and time. Imperial College Press, Singapore, 2010 [4]; Zewail in Science 328:187–193, 2010 [5]; Sciaini and Miller in Rep Prog Phys 74:096101, 2011 [6]; Miller in Annu Rev Phys Chem 65:583–604, 2014 [7]; Vanacore et al. in Nano Today 11:228–249, 2016 [8]). This method, which is called ultrafast electron diffraction or photon-induced near-field electron microscopy (PINEM), where for the former, diffraction patterns are acquired, and for the latter, spectra are acquired, has recently been further developed by several groups around the world (Lee et al. in Struct Dynam-Us 4:044023, 2017 [9]; Feist et al. in Nature 521:200–203, 2015 [10]; Piazza et al. in Nat Commun 6:6407, 2015 [11]; Bucker et al. in European Microscopy Congress 2016: Proceedings. Wiley-VCH Verlag GmbH & Co. KGaA, 2016 [12]; Cao et al. in Sci Rep 5:8404, 2015 [13]) into a time-resolved pump-probe characterization methodology. Photoemission electron guns are currently controlled to create sub-picosecond electron pulses with great spatial coherence, almost at the same level as that of field-driven electron guns (Ehberger et al. in Phys Rev Lett 114:227601, 2015 [14]). Moreover, by controlling the laser-electron jitter by means of microwave or THz cavities, the longitudinal broadening of the electron pulses has been considerably reduced (Walbran et al. in Phys Rev Appl 4:044013, 2015 [15]; Verhoeven et al. in Ultramicroscopy 188:85–89, 2018 [16]; Verhoeven et al. in Struct Dynam-Us 3:054303, 2016 [17]; Maxson et al. in Phys Rev Lett 118:154802, 2017 [18]; Yang et al. in Nat Commun 7:11232, 2016 [19]; Weathersby et al. in Rev Sci Instrum 86:073702, 2015 [20]). Additionally, it was recently demonstrated that the interaction of electron pulses with the laser-induced near field of nanostructures will cause the attosecond bunching of single-electron pulses in space-time (Priebe et al. in Nat Photonics 11:793–797, 2017 [21]). Here, we briefly discuss recent achievements in PINEM, with a focus on the electron-light interactions in the near field of nanoobjects and their combination with time-resolved spectroscopy. After that, we introduce new possibilities by exploring the photon-assisted domain and propose novel methods for revealing the spectral phase and investigating the mutual correlations among photonic systems.

Aligned with the technological developments of electron-based characterization techniques, our theoretical frameworks are yet to be adapted to the strong-laser and slow-electron regimes. More specifically, there exist certain domains where our adiabatic approximations might break down. This is practically important from several viewpoints: (i) in PPM, the shape and amplitude of electron beams are both strongly manipulated, in addition to their phase; (ii) even in free-space electron-light interactions, purely elastic approximations might appear to be a mere over-simplification (Kozak et al. in Nat Phys Lett, 2017 [1]); (iii) during the interaction of electron beams with gratings and light, electron bunching appears to be an additional mechanism to the electron acceleration, where both the acceleration and bunching mechanisms are controlled by the longitudinal broadening of the electron beam relative to the grating period (Talebi in New J Phys 18:123006, 2016 [2]); and (iv) shaped electron beams interacting with matter have different selection rules and might offer approaches for manipulating the electron-induced radiations (Sergeeva et al. in Opt Express 25:26310–26328, 2017 [3]; Tsesses et al. in Phys Rev A 95:013832, 2017 [4]; Kaminer et al. in Phys Rev X 6:011006, 2016 [5]). The last point is fundamentally important, as even for a single electron wave packet, when the electron beam is in a superposition of at least two momentum states, interferences between different quantum paths in the interaction of photons with the electron may occur (Peatross et al. in Phys Rev Lett 100:153601, 2008 [6]). As noted by Keitel and co-workers, the quantum eigenstates of electrons in a nonplanar laser beam or in general shaped light waves are unknown (Peatross et al. in Phys Rev Lett 100:153601, 2008 [6]). For this reason, the development of self-consistent numerical methods may facilitate a better understanding of the outcomes of experiments (Talebi in New J Phys 18:123006, 2016 [2]; White et al. in Phys Rev B 86:205324, 2012 [7]; Kohn et al. in Phys Rev 140:1133, 1965 [8]) and stimulate the design of new experiments.