Showing papers on "Electromagnetic field published in 2020"

Kerr Black Holes as Elementary Particles

Abstract: Long ago, Newman and Janis showed that a complex deformation z → z + ia of the Schwarzschild solution produces the Kerr solution. The underlying explanation for this relationship has remained obscure. The complex deformation has an electromagnetic counterpart: by shifting the Coloumb potential, we obtain the EM field of a certain rotating charge distribution which we term $$ \sqrt{\mathrm{Kerr}} $$ . In this note, we identify the origin of this shift as arising from the exponentiation of spin operators for the recently defined “minimally coupled” three-particle amplitudes of spinning particles coupled to gravity, in the large- spin limit. We demonstrate this by studying the impulse imparted to a test particle in the background of the heavy spinning particle. We first consider the electromagnetic case, where the impulse due to $$ \sqrt{\mathrm{Kerr}} $$ is reproduced by a charged spinning particle; the shift of the Coloumb potential is matched to the exponentiated spin-factor appearing in the amplitude. The known impulse due to the Kerr black hole is then trivially derived from the gravitationally coupled spinning particle via the double copy.

A scalable realization of local U(1) gauge invariance in cold atomic mixtures

Abstract: In the fundamental laws of physics, gauge fields mediate the interaction between charged particles. An example is the quantum theory of electrons interacting with the electromagnetic field, based on U(1) gauge symmetry. Solving such gauge theories is in general a hard problem for classical computational techniques. Although quantum computers suggest a way forward, large-scale digital quantum devices for complex simulations are difficult to build. We propose a scalable analog quantum simulator of a U(1) gauge theory in one spatial dimension. Using interspecies spin-changing collisions in an atomic mixture, we achieve gauge-invariant interactions between matter and gauge fields with spin- and species-independent trapping potentials. We experimentally realize the elementary building block as a key step toward a platform for quantum simulations of continuous gauge theories.

Continuous Wave Second Harmonic Generation Enabled by Quasi-Bound-States in the Continuum on Gallium Phosphide Metasurfaces

Abstract: Resonant metasurfaces are an attractive platform for enhancing the nonlinear optical processes, such as second harmonic generation (SHG), since they can generate large local electromagnetic fields while relaxing the phase-matching requirements. Here, we demonstrate visible range, continuous wave (CW) SHG by combining the attractive material properties of gallium phosphide with high quality-factor photonic modes enabled by bound states in the continuum. We obtain efficiencies around 5e-5% W-1 when the system is pumped at 1200 nm wavelength with CW intensities of 1 kW/cm2. Moreover, we measure external efficiencies of 0.1% W-1 with pump intensities of only 10 MW/cm2 for pulsed irradiation. This efficiency is higher than the values previously reported for dielectric metasurfaces, but achieved here with pump intensities that are two orders of magnitude lower. These results take metasurface-based SHG a step closer to practical applications.

Strong-field nano-optics

Abstract: The present status and development of strong-field nano-optics, an emerging field of nonlinear optics, is discussed. A nonperturbative regime of light-matter interactions is reached when the amplitude of the external electromagnetic fields that are driving a material approach or exceed the field strengths that bind the electrons inside the medium. In this strong-field regime, light-matter interactions depend on the amplitude and phase of the field, rather than its intensity, as in more conventional perturbative nonlinear optics. Traditionally such strong-field interactions have been intensely investigated in atomic and molecular systems, and this has resulted in the generation of high-harmonic radiation and laid the foundations for contemporary attosecond science. Over the past decade, however, a new field of research has emerged, the study of strong-field interactions in solid-state nanostructures. By using nanostructures, specifically those made out of metals, external electromagnetic fields can be localized on length scales of just a few nanometers, resulting in signficantly enhanced field amplitudes that can exceed those of the external field by orders of magnitude in the vicinity of the nanostructures. This leads not only to dramatic enhancements of perturbative nonlinear optical effects but also to significantly increased photoelectron yields. It resulted in a wealth of new phenomena in laser-solid interactions that have been discovered in recent years. These include the observation of above-threshold photoemission from single nanostructures, effects of the carrier-envelope phase on the photoelectron emission yield from metallic nanostructures, and strong-field acceleration of electrons in optical near fields on subcycle timescales. The current state of the art of this field is reviewed, and several scientific applications that have already emerged from the fundamental discoveries are discussed. These include, among others, the coherent control of localized electromagnetic fields at the surface of solid-state nanostructures and of free-electron wave packets by such optical near fields, resulting in the creation of attosecond electron bunches, the coherent control of photocurrents on nanometer length and femtosecond timescales by the electric field of a laser pulse, and the development of new types of ultrafast electron microscopes with unprecedented spatial, temporal, and energy resolution. The review concludes by highlighting possible future developments, discussing emerging topics in photoemission and potential strong-field nanophotonic devices, and giving perspectives for coherent ultrafast microscopy techniques. More generally, it is shown that the synergy between ultrafast science, plasmonics, and strong-field physics holds promise for pioneering scientific discoveries in the upcoming years. (Less)

Phase-Induced Frequency Conversion and Doppler Effect With Time-Modulated Metasurfaces

Abstract: Metasurfaces consisting of electrically thin and densely packed planar arrays of subwavelength elements enable an unprecedented control of the impinging electromagnetic fields. Spatially modulated metasurfaces can efficiently tailor the spatial distribution of these fields with great flexibility. Similarly, time-modulated metasurfaces can be successfully used to manipulate the frequency content and time variations in the impinging field. In this article, we present time-modulated reflective metasurfaces that cause a frequency shift to the impinging radiation, thus realizing an artificial Doppler effect in a nonmoving electrically thin structure. Starting from the theoretical analysis, we analytically derive the required time modulation of the surface admittance to achieve this effect and present a realistic time-varying structure, based on a properly designed and dynamically tuned high-impedance surface. It is analytically and numerically demonstrated that the field emerging from the metasurface is up-/down-converted in frequency according to the modulation profile of the metasurface. The proposed metasurface concept, enabling a frequency modulation of the electromagnetic field “on-the-fly,” may find application in telecommunication, radar, and sensing scenarios.

Radiation reaction in electron–beam interactions with high-intensity lasers

Abstract: Charged particles accelerated by electromagnetic fields emit radiation, which must, by the conservation of momentum, exert a recoil on the emitting particle. The force of this recoil, known as radiation reaction, strongly affects the dynamics of ultrarelativistic electrons in intense electromagnetic fields. Such environments are found astrophysically, e.g. in neutron star magnetospheres, and will be created in laser–matter experiments in the next generation of high-intensity laser facilities. In many of these scenarios, the energy of an individual photon of the radiation can be comparable to the energy of the emitting particle, which necessitates modelling not only of radiation reaction, but quantum radiation reaction. The worldwide development of multi-petawatt laser systems in large-scale facilities, and the expectation that they will create focussed electromagnetic fields with unprecedented intensities $$> 10^{23}\,\mathrm {W}\text {cm}^{-2}$$ , has motivated renewed interest in these effects. In this paper I review theoretical and experimental progress towards understanding radiation reaction, and quantum effects on the same, in high-intensity laser fields that are probed with ultrarelativistic electron beams. In particular, we will discuss how analytical and numerical methods give insight into new kinds of radiation–reaction-induced dynamics, as well as how the same physics can be explored in experiments at currently existing laser facilities.

Pseudo-electromagnetic fields in 3D topological semimetals

Abstract: Dirac and Weyl semimetals react to position-dependent and time-dependent perturbations, such as strain, as if subject to emergent electromagnetic fields, known as pseudo-fields. Pseudo-fields differ from external electromagnetic fields in their symmetries and phenomenology and enable a simple and unified description of a variety of inhomogeneous systems. We review the different physical means of generating pseudo-fields, the observable consequences of pseudo-fields and their similarities to and differences from electromagnetic fields. Among these differences is their effect on quantum anomalies — absences of classical symmetries in the quantum theory — which we revisit from a quantum field theory and a semi-classical viewpoint. We conclude with predicted observable signatures of the pseudo-fields and the status of the nascent experimental research. Pseudo-electromagnetic fields emerge in inhomogeneous materials. This Review discusses the properties of such fields in the context of 3D topological semimetals, the origin and consequences of pseudo-fields in real materials and their field theory description.

From cavity to circuit quantum electrodynamics

Abstract: Circuit quantum electrodynamics focuses on the interaction of small superconducting circuits, tailored to behave as two-level quantum systems, with a single mode of the electromagnetic field sustained by a superconducting resonator. It is thus concerned with the investigation of phenomena that arise from the coupling between the simplest non-trivial quantum system — a spin-1/2 or qubit — and a harmonic oscillator. As such, circuit quantum electrodynamics belongs to the more general field of cavity quantum electrodynamics, which deals with natural or artificial spins in the optical, microwave or radio-frequency domains interacting with all kind of resonators. Here we survey the lineage of the concepts and experiments that led first to the development of cavity and then circuit quantum electrodynamics. We discuss similarities and differences between these two fields and compare their present achievements. This article puts in perspective the relationship between cavity and circuit quantum electrodynamics, two related approaches for studying the fundamental quantum interaction between light and matter.

A Theoretical and Experimental Investigation on the Measurement of the Electromagnetic Field Level Radiated by 5G Base Stations

Abstract: This paper presents some theoretical considerations and experimental results regarding the problem of maximum power extrapolation for the assessment of the exposure to electromagnetic fields radiated by 5G base stations. In particular the results of an extensive experimental campaign using an extrapolation procedure recently proposed for 5G signal is discussed and experimentally checked on a SU-MIMO signal. The results confirm the effectiveness of the extrapolation technique. Starting from an analysis (that represents a further novel contribution of this paper) on the impact of Spatial Division Multiple Access techniques used in 5G on the measurement of EMF level, some indications of possible extension of the technique to the highly complex MU-MIMO case are also given.

Covariant spin kinetic theory I: collisionless limit *

Abstract: We develop a covariant kinetic theory for massive fermions in a curved spacetime and an external electromagnetic field based on quantum field theory. We derive four coupled semi-classical kinetic equations accurate to \begin{document}$O(\hbar)$\end{document} , which describe the transports of particle number and spin degrees of freedom. The relationship with chiral kinetic theory is discussed. As an application, we study spin polarization in the presence of finite Riemann curvature and an electromagnetic field in both local and global equilibrium states.

Laser produced electromagnetic pulses : Generation, detection and mitigation

Abstract: This paper provides an up-to-date review of the problems related to the generation, detection and mitigation of strong electromagnetic pulses created in the interaction of high-power, high-energy laser pulses with different types of solid targets. It includes new experimental data obtained independently at several international laboratories. The mechanisms of electromagnetic field generation are analyzed and considered as a function of the intensity and the spectral range of emissions they produce. The major emphasis is put on the gHz frequency domain, which is the most damaging for electronics and may have important applications. The physics of electromagnetic emissions in other spectral domains, in particular THz and MHz, is also discussed. The theoretical models and numerical simulations are compared with the results of experimental measurements, with special attention to the methodology of measurements and complementary diagnostics. Understanding the underlying physical processes is the basis for developing techniques to mitigate the electromagnetic threat and to harness electromagnetic emissions, which may have promising applications.

Covariant Spin Kinetic Theory I: Collisionless Limit

Abstract: We develop a covariant kinetic theory for massive fermions in curved spacetime and external electromagnetic field based on quantum field theory. We derive four coupled semi-classical kinetic equations accurate at $O(\hbar)$, which describe the transports of particle number and spin degrees of freedom. The relation with the chiral kinetic theory is discussed. As an application, we study the spin polarization in the presence of finite Riemann curvature and electromagnetic field in both local and global equilibrium states.

Maxwellian evolution equations along the uniform optical fiber in Minkowski space

Abstract: We firstly discuss the geometric phase rotation for an electromagnetic wave traveling along the optical fiber in Minkowski space We define two types of novel geometric phases associated with the evolution of the polarization vectors in the normal and binormal directions along the optical fiber by identifying the normal-Rytov parallel transportation law and binormal-Rytov parallel transportation law and derive their relationships with the new types of Fermi-Walker transportation law in Minkowski space Then we describe a novel approach of solving Maxwell's equations in terms of electromagnetic field vectors and geometric quantities associated with the curved path characterizing the path uniform optical fiber by using the traveling wave transformation method Finally, we investigate that electromagnetic wave propagation along the uniform optical fiber admits an interesting family of Maxwellian evolution equation having numerous physical and geometric applications for anholonomic coordinate system in Minkowski space

Design of DD Coil With High Misalignment Tolerance and Low EMF Emissions for Wireless Electric Vehicle Charging Systems

Abstract: In this article, a design method of the double-D (DD) coil aiming at high misalignment tolerance is proposed, and the electromagnetic field (EMF) shielding of the system is considered. Inspired by the DD coil recommended in the standard J2954 published by the Society of Automotive Engineers, the novel structures of the transmitting (Tx) coil and the receiving (Rx) coil are designed, respectively. First, the standard DD coil is introduced as a reference. Second, for the Tx coil, the parameters, such as length, width, and coverage, are investigated in detail. For the Rx coil, the coil structure overlapped in the edge is optimized. The purpose is to obtain a higher coupling coefficient at the maximum offset. Third, considering EMF emissions exceeding the limit, the structure of the central-depressed coil with E-shaped cores is proposed in the Tx coil. The EMF emissions can be reduced to less than 27 μ T at the rated output power. Finally, a 6.6–kW experimental system of which the maximum transmission efficiency is higher than 94% is set up. The experimental results prove that the proposed structure is beneficial to maintain a higher coupling coefficient against misalignment and suppress EMF emissions.

Quasinormal modes, shadow, and greybody factors of 5D electrically charged Bardeen black holes

Abstract: We study quasinormal modes (QNMs) in a five-dimensional electrically charged Bardeen black hole spacetime by considering the scalar and electromagnetic field perturbations. The black hole spacetime is an exact solution of Einstein gravity coupled to nonlinear electrodynamics in five dimensions, which has nonsingular behavior. To calculate QNMs, we use the WKB approximation method up to sixth order. Due to the presence of electric charge ${q}_{e}g0$, both the scalar and electromagnetic field perturbations decay more slowly when compared to the Schwarzschild-Tangherlini black holes. We discover that the scalar field perturbations oscillate more rapidly compared to the electromagnetic field perturbations. In terms of damping, the scalar field perturbations damp more rapidly. We graphically show that the transmission (reflection) coefficients decrease (increase) with an increase in the magnitude of the electric charge ${q}_{e}$. The emission of gravitational waves allows the spacetime to undergo damped oscillations due to the nonzero value of the imaginary part, which is always negative. The imaginary part of the QNM frequencies continuously decreases with an increase in the magnitude of the electric charge ${q}_{e}$ for a given mode ($l$, $n$). A connection between the QNM frequencies and the black hole shadow, as well as the geometric cross section in the eikonal limit, is also described.

Bianisotropy for light trapping in all-dielectric metasurfaces

Abstract: Magnetoelectric dipole coupling effects in all-dielectric metasurfaces composed of particles with bianisotropic electromagnetic response are investigated. This bianisotropic response is associated with the trapped mode excitation. Maintaining the trapped mode resonant conditions allows one to sufficiently increase the quality factor and reduce radiation losses in all-dielectric nanostructures (metasurfaces). An analytical model accounting for the contributions of both electric and magnetic dipole moments induced in particles by external electromagnetic fields is proposed. We show how bianisotropy can lead to the excitation of the trapped mode in metasurfaces. This mode corresponds to the electromagnetic coupling between the out-of-plane particle dipole moments, which do not radiate collectively from the metasurface plane resulting in the enhanced storage of electromagnetic energy. Our approach reveals a physical mechanism of the trapped mode excitation and demonstrates that the specially initiated bianisotropy of particles enables the energy flow between external electromagnetic waves and the trapped mode. Due to this bianisotropy, one can control the process of light-matter interaction and energy storage in all-dielectric metasurfaces via excitation of trapped modes.

On the numerical investigation of the interaction in plasma between (high & low) frequency of (Langmuir & ion–acoustic) waves

Abstract: In this paper, the Zakharov (Z.) equation in the dimensionless form is numerically investigated via (Cubic & Quantic & Septic) B-spline schemes to demonstrate the fidelity of the calculated computational solutions. The Z equation depicts the interaction in plasma between (high & low) frequency of (Langmuir & ion-acoustic) waves. This interaction is expounded in the prompts of the coastal engineering, electromagnetic field, signal handling in the optical fibres, plasma physics, and fluid dynamics. Three different computational schemes were applied to the Z equation for constructing many novel analytical solutions. In our paper, we try to check the accuracy of these solutions via the above-mentioned numerical schemes. Moreover, some separate sketches are given to indicate more physical features of this interaction. The originality of the obtained solutions is investigated by showing the similarities and differences between our obtained solutions and that was purchased in previously published papers.

A gyrokinetic model for the plasma periphery of tokamak devices

Abstract: A gyrokinetic model is presented that can properly describe large and small amplitude electromagnetic fluctuations occurring on scale lengths ranging from the electron Larmor radius to the equilibrium perpendicular pressure gradient scale length, and the arbitrarily large deviations from thermal equilibrium that are present in the plasma periphery of tokamak devices. The formulation of the gyrokinetic model is based on a second-order accurate description of the single charged particle dynamics, derived from Lie perturbation theory, where the fast particle gyromotion is decoupled from the slow drifts assuming that the ratio of the ion sound Larmor radius to the perpendicular equilibrium pressure scale length is small. The collective behaviour of the plasma is obtained by a gyrokinetic Boltzmann equation that describes the evolution of the gyroaveraged distribution function. The collisional effects are included by a nonlinear gyrokinetic Dougherty collision operator. The gyrokinetic model is then developed into a set of coupled fluid equations referred to as the gyrokinetic moment hierarchy. To obtain this hierarchy, the gyroaveraged distribution function is expanded onto a Hermite–Laguerre velocity-space polynomial basis. Then, the gyrokinetic equation is projected onto the same basis yielding the spatial and temporal evolution of the Hermite–Laguerre expansion coefficients. A closed set of fluid equations for the lowest-order coefficients is presented. The Hermite–Laguerre projection is performed accurately at arbitrary perpendicular wavenumber values. Finally, the self-consistent evolution of the electromagnetic fields is described by a set of gyrokinetic Maxwell equations derived from a variational principle where the velocity integrals are explicitly evaluated.

Analytical solutions of time-fractional heat order for a magneto-photothermal semiconductor medium with Thomson effects and initial stress

Abstract: The influence of hydrostatic initial stress in the context of the time-fractional heat order equation is investigated The strong electromagnetic field is applied at the external surface of semiconductor elastic medium during the photothermal transport process The Thomson influence appears due to the strong magnetic field The behavior of wave propagations of the elastic medium is obtained in context of the thermoelectricity theory with initial stress The governing main equations are taken in two dimensions to describe the interaction between elastic-thermal-plasma and electromagnetic waves for fractional cases The density of charge is studied as a function of time only when the electric current is induced The separation of variables is used as a mathematical technique to obtain the exact solutions of the distributions of physical quantities under investigation Some mechanical, thermal, plasma and magnetic conditions are applied at the free surface elastic medium A numerical simulation is used to obtain physical quantities distributions graphically and discussed theoretically in various fractional cases

Fundamental limits to radiative heat transfer: Theory

Abstract: Radiative heat transfer between bodies at the nanoscale can surpass blackbody limits on thermal radiation by orders of magnitude due to contributions from evanescent electromagnetic fields, which carry no energy to the far field. Thus far, principles guiding explorations of larger heat transfer beyond planar structures have assumed utility in surface nanostructuring, via enhancement of the density of states, and the possibility that such design paradigms can approach Landauer limits, in analogy to conduction. Here we derive fundamental shape-independent limits to radiative heat transfer, applicable in near- through far-field regimes, that incorporate material and geometric constraints such as intrinsic dissipation and finite object sizes, and show that these preclude reaching the Landauer limits in all but a few restrictive scenarios. Additionally, we show that the interplay of material response and electromagnetic scattering among proximate bodies means that bodies which maximize radiative heat transfer actually maximize scattering rather than absorption. Finally, we compare our new bounds to Landauer limits as well as limits that ignore the interplay between material and geometric constraints, and show that these prior limits lead to overly optimistic predictions. Our results have ramifications for the ultimate performance of thermophotovoltaics and nanoscale cooling, as well as incandescent and luminescent devices.

Spatially structured transparency and transfer of optical vortices via four-wave mixing in a quantum-dot nanostructure

Abstract: We propose a scheme to generate structured light using a medium consisting of semiconductor quantum dots via four-wave mixing (FWM). We consider a four-level quantum-dot structure where two strong electromagnetic fields couple upper-level biexciton transitions, whereas a weak field is applied to one of the ground-level exciton transitions. A weak signal field is generated, corresponding to a second ground-level exciton transition; thus the overall configuration transforms into a closed-loop diamond-type shape. To realize a spatially dependent modulating quantum-dot medium, we consider strong coupling fields as structured lights and investigate different regions of spatially structured electromagnetically induced transparency via absorption of the generated signal field. The azimuthal phase-dependent modulation of the absorption profile of the generated signal field is the key factor behind the creation of structured light. In addition, we also demonstrate transfer of orbital angular momentum (OAM) of the control beam to the generated beam through the FWM process and study the effect of phase mismatch on efficiency of the OAM transfer.

Probing vacuum polarization effects with high-intensity lasers

Abstract: These notes provide a pedagogical introduction to the theoretical study of vacuum polarization effects in strong electromagnetic fields as provided by state-of-the-art high-intensity lasers. Quantum vacuum fluctuations give rise to effective couplings between electromagnetic fields, thereby supplementing Maxwell’s linear theory of classical electrodynamics with nonlinearities. Resorting to a simplified laser pulse model, allowing for explicit analytical insights, we demonstrate how to efficiently analyze all-optical signatures of these effective interactions in high-intensity laser experiments. Moreover, we highlight several key features relevant for the accurate planning and quantitative theoretical analysis of quantum vacuum nonlinearities in the collision of high-intensity laser pulses.

Active particles as mobile microelectrodes for selective bacteria electroporation and transport.

Abstract: Self-propelling micromotors are emerging as a promising micro- and nanoscale tool for single-cell analysis. We have recently shown that the field gradients necessary to manipulate matter via dielectrophoresis can be induced at the surface of a polarizable active ("self-propelling") metallodielectric Janus particle (JP) under an externally applied electric field, acting essentially as a mobile floating microelectrode. Here, we successfully demonstrated that the application of an external electric field can singularly trap and transport bacteria and can selectively electroporate the trapped bacteria. Selective electroporation, enabled by the local intensification of the electric field induced by the JP, was obtained under both continuous alternating current and pulsed signal conditions. This approach is generic and applicable to bacteria and JP, as well as a wide range of cell types and micromotor designs. Hence, it constitutes an important and novel experimental tool for single-cell analysis and targeted delivery.

A primary model of THz and far-infrared signal generation and conduction in neuron systems based on the hypothesis of the ordered phase of water molecules on the neuron surface I: signal characteristics

Abstract: In this paper, we use the theory of quantum optics and electrodynamics to study the electromagnetic field problem in the nervous system based on the assumption of an ordered arrangement of water molecules on the neuronal surface. Using the Lagrangian of the water molecule-field ion, the dynamic equations for neural signal generation and transmission are derived. Perturbation theory and the numerical method are used to solve the dynamic equations, and the characteristics of high-frequency signals (the dispersion relation, the time domain of the field, the frequency domain waveform, etc.) are discussed. This model predicts some intrinsic vibration modes of electromagnetic radiation on the neuronal surface. The frequency range of these vibration modes is in the THz and far-infrared ranges.

Infrared dielectric metamaterials from high refractive index chalcogenides

Abstract: High-index dielectric materials are in great demand for nanophotonic devices and applications, from ultrathin optical elements to metal-free sub-diffraction light confinement and waveguiding. Here we show that chalcogenide topological insulators are particularly apt candidates for dielectric nanophotonics architectures in the infrared spectral range, by reporting metamaterial resonances in chalcogenide crystals sustained well inside the mid-infrared, choosing Bi2Te3 as case study within this family of materials. Strong resonant modulation of the incident electromagnetic field is achieved thanks to the exceptionally high refractive index ranging between 7 and 8 throughout the 2–10 μm region. Analysis of the complex mode structure in the metamaterial allude to the excitation of circular surface currents which could open pathways for enhanced light-matter interaction and low-loss plasmonic configurations by coupling to the spin-polarized topological surface carriers, thereby providing new opportunities to combine dielectric, plasmonic and magnetic metamaterials in a single platform. High-index dielectric materials are in great demand for nanophotonic applications. Here, the authors show that chalcogenide topological insulators are suitable candidates for dielectric nanophotonics in the infrared spectral range by reporting resonances in Bi2Te3 crystals sustained in the mid-infrared.

Direct visualization of electromagnetic wave dynamics by laser-free ultrafast electron microscopy.

Abstract: Integrating femtosecond lasers with electron microscopies has enabled direct imaging of transient structures and morphologies of materials in real time and space. Here, we report the development of a laser-free ultrafast electron microscopy (UEM) offering the same capability but without requiring femtosecond lasers and intricate instrumental modifications. We create picosecond electron pulses for probing dynamic events by chopping a continuous beam with a radio frequency (RF)-driven pulser with the pulse repetition rate tunable from 100 MHz to 12 GHz. As a first application, we studied gigahertz electromagnetic wave propagation dynamics in an interdigitated comb structure. We reveal, on nanometer space and picosecond time scales, the transient oscillating electromagnetic field around the tines of the combs with time-resolved polarization, amplitude, and local field enhancement. This study demonstrates the feasibility of laser-free UEM in real-space visualization of dynamics for many research fields, especially the electrodynamics in devices associated with information processing technology.