arXiv subjects

Ido Kaminer

Publications and source records attributed to Ido Kaminer.

At least 127 records · Page 7Linked to original sources

arXiv2019

Ultrashort Tilted-Pulse-Front Pulses and Nonparaxial Tilted-Phase-Front Beams

Electromagnetic pulses with tilted pulse fronts are instrumental in enhancing the efficiency of many light-matter interaction processes, with prominent examples including terahertz generation by optical rectification, dielectric laser acceleration, ultrafast electron imaging and X-ray generation from free electron lasers. Here, we find closed-form expressions for tilted-pulse-front pulses that capture their exact propagation dynamics even in deeply nonparaxial and sub-single-cycle regimes. By studying the zero-bandwidth counterparts of these pulses, we further obtain classes of nondiffracting wavepackets whose phase fronts are tilted with respect to the direction of travel of the intensity peak. The intensity profile of these nonparaxial nondiffracting wavepackets move at a constant velocity that can be much greater than or much less than the speed of light, and can even travel backwards relative to the direction of phase front propagation.

physics.optics↗

arXiv2019

Maximal Spontaneous Photon Emission and Energy Loss from Free Electrons

Free electron radiation such as Cerenkov, Smith--Purcell, and transition radiation can be greatly affected by structured optical environments, as has been demonstrated in a variety of polaritonic, photonic-crystal, and metamaterial systems. However, the amount of radiation that can ultimately be extracted from free electrons near an arbitrary material structure has remained elusive. Here we derive a fundamental upper limit to the spontaneous photon emission and energy loss of free electrons, regardless of geometry, which illuminates the effects of material properties and electron velocities. We obtain experimental evidence for our theory with quantitative measurements of Smith--Purcell radiation. Our framework allows us to make two predictions. One is a new regime of radiation operation---at subwavelength separations, slower (nonrelativistic) electrons can achieve stronger radiation than fast (relativistic) electrons. The second is a divergence of the emission probability in the limit of lossless materials. We further reveal that such divergences can be approached by coupling free electrons to photonic bound states in the continuum (BICs). Our findings suggest that compact and efficient free-electron radiation sources from microwaves to the soft X-ray regime may be achievable without requiring ultrahigh accelerating voltages.

physics.optics↗

arXiv2018

Experimental observation of superscattering

Superscattering, induced by degenerate resonances, breaks the fundamental single-channel limit of scattering cross section of subwavelength structures; in principle, an arbitrarily large total cross section can be achieved via superscattering. It thus provides a unique way to strengthen the light-matter interaction at the subwavelength scale, and has many potential applications in sensing, energy harvesting, bio-imaging (such as magnetic resonance imaging), communication and optoelectronics. However, the experimental demonstration of superscattering remains an open challenge due to its vulnerability to structural imperfections and intrinsic material losses. Here we report the first experimental evidence for superscattering, by demonstrating the superscattering simultaneously in two different frequency regimes through both the far-field and near-field measurements. The underlying mechanism for the observed superscattering is the degenerate resonances of confined surface waves, by utilizing a subwavelength metasurface-based multilayer structure. Our work paves the way towards practical applications based on superscattering.

physics.class-ph↗

arXiv2018

Extreme enhancement of spin relaxation mediated by surface magnon polaritons

Polaritons in metals, semimetals, semiconductors, and polar insulators, with their extreme confinement of electromagnetic energy, provide many promising opportunities for enhancing typically weak light-matter interactions such as multipolar radiation, multiphoton spontaneous emission, Raman scattering, and material nonlinearities. These highly confined polaritons are quasi-electrostatic in nature, with most of their energy residing in the electric field. As a result, these "electric" polaritons are far from optimized for enhancing emission of a magnetic nature, such as spin relaxation, which is typically many orders of magnitude slower than corresponding electric decays. Here, we propose using surface magnon polaritons in negative magnetic permeability materials such as MnF$_2$ and FeF$_2$ to strongly enhance spin-relaxation in nearby emitters in the THz spectral range. We find that these magnetic polaritons in 100 nm thin-films can be confined to lengths over 10,000 times smaller than the wavelength of a photon at the same frequency, allowing for a surprising twelve orders of magnitude enhancement in magnetic dipole transitions. This takes THz spin-flip transitions, which normally occur at timescales on the order of a year, and forces them to occur at sub-ms timescales. Our results suggest an interesting platform for polaritonics at THz frequencies, and more broadly, a new way to use polaritons to control light-matter interactions.

physics.optics↗

arXiv2018

Superlight inverse Doppler effect

There is a century-old tenet [1, 2] that the inverse Doppler frequency shift of light [3-13] is impossible in homogeneous systems with a positive refractive index. Here we break this long-held tenet by predicting a new kind of Doppler effect of light inside the Cherenkov cone. Ever since the classic work of Ginzburg and Frank, it has been known that a superlight (i.e., superluminal) normal Doppler effect [14-18] appears inside the Cherenkov cone when the velocity of the source v is larger than the phase velocity of light v_p. By further developing their theory we discover that an inverse Doppler frequency shift will arise when v>2v_p. We denote this as the superlight inverse Doppler effect. Moreover, we show that the superlight inverse Doppler effect can be spatially separated from the other Doppler effects by using highly squeezed polaritons (such as graphene plasmons), which may facilitate the experimental observation.

physics.optics↗

arXiv2018

Efficient orbital angular momentum transfer between plasmons and free electrons

Free electrons can efficiently absorb or emit plasmons excited in a thin conductor, giving rise to multiple energy peaks in the transmitted electron spectra separated by multiples of the plasmon energy. When the plasmons are chiral, this can also give rise to transfer of orbital angular momentum (OAM). Here, we show that large amounts of OAM can be efficiently transferred between chiral plasmons supported by a thin film and free electrons traversing it. Under realistic conditions, our predictive simulations reveal efficient absorption of $\ell\gg1$ chiral plasmons of vorticity $m\gg1$, resulting in an OAM transfer $\ell m\hbar\gg\hbar$. Our work supports the use of chiral plasmons sustained by externally illuminated thin films as a way of generating high-vorticity electrons, resulting in a remarkably large fraction of kinetic energy associated with motion along the azimuthal direction, perpendicular to the incident beam.

cond-mat.mes-hall↗

arXiv2018

Controlling Cherenkov angles with resonance transition radiation

Cherenkov radiation provides a valuable way to identify high energy particles in a wide momentum range, through the relation between the particle velocity and the Cherenkov angle. However, since the Cherenkov angle depends only on material's permittivity, the material unavoidably sets a fundamental limit to the momentum coverage and sensitivity of Cherenkov detectors. For example, Ring Imaging Cherenkov detectors must employ materials transparent to the frequency of interest as well as possessing permittivities close to unity to identify particles in the multi GeV range, and thus are often limited to large gas chambers. It would be extremely important albeit challenging to lift this fundamental limit and control Cherenkov angles as preferred. Here we propose a new mechanism that uses constructive interference of resonance transition radiation from photonic crystals to generate both forward and backward Cherenkov radiation. This mechanism can control Cherenkov angles in a flexible way with high sensitivity to any desired range of velocities. Photonic crystals thus overcome the severe material limit for Cherenkov detectors, enabling the use of transparent materials with arbitrary values of permittivity, and provide a promising option suited for identification of particles at high energy with enhanced sensitivity.

physics.app-ph↗

arXiv2018

Multifrequency superscattering from subwavelength hyperbolic structures

Superscattering, i.e., a phenomenon of the scattering cross section from a subwavelength object exceeding the single-channel limit, has important prospects in enhanced sensing/spectroscopy, solar cells, and biomedical imaging. Superscattering can be typically constructed only at a single frequency regime, and depends critically on the inescapable material losses. Under such realistic conditions, superscattering has not been predicted nor observed to exist simultaneously at multiple frequency regimes. Here we introduce multifrequency superscattering in a subwavelength hyperbolic structure, which can be made from artificial metamaterials or from naturally-existing materials, such as hexagonal boron nitride (BN), and show the advantage of such hyperbolic materials for reducing structural complexity. The underlying mechanism is revealed to be the multimode resonances at multiple frequency regimes as appear in BN due to the peculiar dispersion of phonon-polaritons. Importantly, the multifrequency superscattering has a high tolerance to material losses and some structural variations, bringing the concept of multifrequency superscattering closer to useful and realistic conditions.

physics.optics↗

arXiv2017

Shaping Long-lived Electron Wavepackets for Customizable Optical Spectra

Electrons in atoms and molecules are versatile physical systems covering a vast range of light-matter interactions, enabling the physics of Rydberg states, photon-photon bound states, simulation of condensed matter Hamiltonians, and quantum sources of light. A limitation on the versatility of such electronic systems for optical interactions would appear to arise from the discrete nature of the electronic transitions and from the limited ionization energy, constraining the energy scale through which the rich physics of bound electrons can be accessed. In this work, we propose the concept of shaping spatially confined electron wavepackets as superpositions of extended states in the ionization continuum. These wavepackets enable customizable optical emission spectra transitions in the eV-keV range. We find that the specific shaping lengthens the diffraction lifetime of the wavepackets in exchange for increasing their spatial spreads. Finally, we study the spontaneous radiative transitions of these excited states, examining the influence of the wavepacket shape and size on the radiation rate of the excited state. We observe that the rate of radiative capture is primarily limited by the diffraction lifetime of the wavepacket. The approach proposed in this work could have applications towards developing designer emitters at tunable energy and length scales, potentially bringing the physics of Rydberg states to new energy scales and extending the range and versatility of emitters that can be developed using shaped electrons.

quant-ph↗

arXiv2017

Controlling light emission with electron wave interference

It is a long standing question whether or not one can change the nature of spontaneous emission by a free electron through shaping the electron wavefunction. On one hand, shaping the electron wavefunction changes the respective charge and current densities of the electron. On the other hand, spontaneous emission of an electron is an incoherent process and can often be insensitive to the shape of the electron wavefunction. In this work, we arrive at an affirmative answer examining Bremsstrahlung radiation by free electron superposition states. We find that the radiation can be markedly different from an incoherent sum of the radiations of the two states because of interference of the radiation amplitudes from the two components of the superposition. The ability to control free electron spontaneous emission via interference may eventually result in a new degree of control over radiation over the entire electromagnetic spectrum in addition to the ability to deterministically introduce quantum behavior into normally classical light emission processes.

quant-ph↗

arXiv2017

Smith-Purcell Radiation from Low-Energy Electrons

Recent advances in the fabrication of nanostructures and nanoscale features in metasurfaces offer a new prospect for generating visible, light emission from low energy electrons. In this paper, we present the experimental observation of visible light emission from low-energy free electrons interacting with nanoscale periodic surfaces through the Smith-Purcell (SP) effect. SP radiation is emitted when electrons pass in close proximity over a periodic structure, inducing collective charge motion or dipole excitations near the surface, thereby giving rise to electromagnetic radiation. We demonstrate a controlled emission of SP light from nanoscale gold gratings with periodicity as small as 50 nm, enabling the observation of visible SP radiation by low energy electrons (1.5 to 6 keV), an order of magnitude lower than previously reported. We study the emission wavelength and intensity dependence on the grating pitch and electron energy, showing agreement between experiment and theory. Further reduction of structure periodicity should enable the production of SP-based devices that operate with even slower electrons that allow an even smaller footprint and facilitate the investigation of quantum effects for light generation in nanoscale devices. A tunable light source integrated in an electron microscope would enable the development of novel electron-optical correlated spectroscopic techniques, with additional applications ranging from biological imaging to solid-state lighting.

physics.optics↗

arXiv2017

Spectral and spatial shaping of Smith Purcell Radiation

The Smith Purcell effect, observed when an electron beam passes in the vicinity of a periodic structure, is a promising platform for the generation of electromagnetic radiation in previously-unreachable spectral ranges. However, most of the studies of this radiation were performed on simple periodic gratings, whose radiation spectrum exhibits a single peak and its higher harmonics predicted by a well-established dispersion relation. Here, we propose a method to shape the spatial and spectral far-field distribution of the radiation using complex periodic and aperiodic gratings. We show, theoretically and experimentally, that engineering multiple peak spectra with controlled widths located at desired wavelengths is achievable using Smith-Purcell radiation. Our method opens the way to free-electron driven sources with tailored angular and spectral response, and gives rise to focusing functionality for spectral ranges where lenses are unavailable or inefficient.

physics.optics↗

arXiv2017

Tunable UV-Emitters through Graphene Plasmons

Control over the spontaneous emission of light through tailored optical environments remains a fundamental paradigm in nanophotonics. The use of highly-confined plasmons in materials such as graphene provides a promising platform to enhance transition rates in the IR-THz by many orders of magnitude. However, such enhancements involve near-field plasmon modes or other kinds of near-field coupling like quenching, and it is challenging to use these highly confined modes to harness light in the far-field due to the difficulty of plasmonic outcoupling. Here, we propose that through the use of radiative cascade chains in multi-level emitters, IR plasmons can be used to enhance far field spectra in the visible and UV range, even at energies greater than 10 eV. Combining Purcell-enhancement engineering, graphene plasmonics, and radiative cascade can result in a new type of UV emitter whose properties can be tuned by electrically doping graphene. Varying the distance between the emitter and the graphene surface can change the strength of the far-field emission lines by two orders of magnitude. We also find that the dependence of the far-field emission on the Fermi energy is potentially extremely sharp at the onset of interband transitions, allowing the Fermi energy to effectively serve as a "switch" for turning on and off certain plasmonic and far-field emissions.

physics.optics↗

arXiv2017

Shaping Polaritons to Reshape Selection Rules

The discovery of orbital angular momentum (OAM) in light established a new degree of freedom by which to control not only its flow but also its interaction with matter. Here, we show that by shaping extremely sub-wavelength polariton modes, for example by imbuing plasmon and phonon polariton with OAM, we engineer which transitions are allowed or forbidden in electronic systems such as atoms, molecules, and artificial atoms. Crucial to the feasibility of these engineered selection rules is the access to conventionally forbidden transitions afforded by sub-wavelength polaritons. We also find that the position of the absorbing atom provides a surprisingly rich parameter for controlling which absorption processes dominate over others. Additional tunability can be achieved by altering the polaritonic properties of the substrate, for example by tuning the carrier density in graphene, potentially enabling electronic control over selection rules. Our findings are best suited to OAM-carrying polaritonic modes that can be created in graphene, monolayer conductors, thin metallic films, and thin films of polar dielectrics such as boron nitride. By building on these findings we foresee the complete engineering of spectroscopic selection rules through the many degrees of freedom in the shape of optical fields.

physics.optics↗

arXiv2017

All-angle negative refraction of highly squeezed plasmon and phonon polaritons in graphene-boron nitride heterostructures

A fundamental building block for nanophotonics is the ability to achieve negative refraction of polaritons, because this could enable the demonstration of many unique nanoscale applications such as deep-subwavelength imaging, superlens, and novel guiding. However, to achieve negative refraction of highly squeezed polaritons, such as plasmon polaritons in graphene and phonon polaritons in boron nitride (BN) with their wavelengths squeezed by a factor over 100, requires the ability to flip the sign of their group velocity at will, which is challenging. Here we reveal that the strong coupling between plasmon and phonon polaritons in graphene-BN heterostructures can be used to flip the sign of the group velocity of the resulting hybrid (plasmon-phonon-polariton) modes. We predict all-angle negative refraction between plasmon and phonon polaritons, and even more surprisingly, between hybrid graphene plasmons, and between hybrid phonon polaritons. Graphene-BN heterostructures thus provide a versatile platform for the design of nano-metasurfaces and nano-imaging elements.

physics.optics↗

arXiv2017

A near-unity efficiency source of entangled guided waves

Surface phonon polaritons are hybrid modes of photons and optical phonons that can propagate on the surface of a polar dielectric. In this work, we show that the precise combination of confinement and bandwidth offered by surface phonon polaritons allows for the ability to create highly efficient sources of entangled light in the IR/THz. Specifically, phonon polaritons can cause emitters to preferentially decay by the emission of pairs of surface phonon polaritons, instead of the previously dominant single-photon emission. We show that such two-photon emission processes can occur on nanosecond time-scales and can be nearly two orders of magnitude faster than competing single-photon transitions, as opposed to being as much as eight to ten orders of magnitude slower in free space. Our results suggest a fundamentally new design strategy for quantum light sources in the IR/THz: ones that prefer to emit a relatively broad spectrum of entangled photons, potentially allowing for new sources of both single and multiple photons.

physics.optics↗

arXiv2016

Laser-Induced Linear Electron Acceleration in Free Space

Linear acceleration in free space is a topic that has been studied for over 20 years, and its ability to eventually produce high-quality, high energy multi-particle bunches has remained a subject of great interest. Arguments can certainly be made that such an ability is very doubtful. Nevertheless, we chose to develop an accurate and truly predictive theoretical formalism to explore this remote possibility in a computational experiment. The formalism includes exact treatment of Maxwell's equations, exact relativistic treatment of the interaction among the multiple individual particles, and exact treatment of the interaction at near and far field. Several surprising results emerged. For example, we find that 30 keV electrons (2.5% energy spread) can be accelerated to 7.7 MeV (2.5% spread) and to 205 MeV (0.25% spread) using 25 mJ and 2.5 J lasers respectively. These findings should hopefully guide and help develop compact, high-quality, ultra-relativistic electron sources, avoiding conventional limits imposed by material breakdown or structural constraints.

physics.acc-ph↗

arXiv2016

Tailoring the energy distribution and loss of 2D plasmons

The ability to tailor the energy distribution of plasmons at the nanoscale has many applications in nanophotonics, such as designing plasmon lasers, spasers, and quantum emitters. To this end, we analytically study the energy distribution and the proper field quantization of 2D plasmons with specific examples for graphene plasmons. We find that the portion of the plasmon energy contained inside graphene (energy confinement factor) can exceed 50%, despite graphene being infinitely thin. In fact, this very high energy confinement can make it challenging to tailor the energy distribution of graphene plasmons just by modifying the surrounding dielectric environment or the geometry, such as changing the separation distance between two coupled graphene layers. However, by adopting concepts of parity-time symmetry breaking, we show that tuning the loss in one of the two coupled graphene layers can simultaneously tailor the energy confinement factor and propagation characteristics, causing the phenomenon of loss-induced plasmonic transparency.

physics.optics↗