Electromagnetic Field Profiles Research Articles

Photonic Angular Momentum in Intense Light–Matter Interactions

Light contains both spin and orbital angular momentum. Despite contributing equally to the total photonic angular momentum, these components derive from quite different parts of the electromagnetic field profile, namely its polarization and spatial variation, respectively, and therefore do not always share equal influence in light–matter interactions. With the growing interest in utilizing light’s orbital angular momentum to practice added control in the study of atomic systems, it becomes increasingly important for students and researchers to understand the subtlety involved in these interactions. In this article, we present a review of the fundamental concepts and recent experiments related to the interaction of beams containing orbital angular momentum with atoms. An emphasis is placed on understanding light’s angular momentum from the perspective of both classical waves and individual photons. We then review the application of these beams in recent experiments, namely single- and few-photon transitions, strong-field ionization, and high-harmonic generation, highlighting the role of light’s orbital angular momentum and the atom’s location within the beam profile within each case.

Quantum annealing-aided design of an ultrathin-metamaterial optical diode

Thin-film optical diodes are important elements for miniaturizing photonic systems. However, the design of optical diodes relies on empirical and heuristic approaches. This poses a significant challenge for identifying optimal structural models of optical diodes at given wavelengths. Here, we leverage a quantum annealing-enhanced active learning scheme to automatically identify optimal designs of 130 nm-thick optical diodes. An optical diode is a stratified volume diffractive film discretized into rectangular pixels, where each pixel is assigned to either a metal or dielectric. The proposed scheme identifies the optimal material states of each pixel, maximizing the quality of optical isolation at given wavelengths. Consequently, we successfully identify optimal structures at three specific wavelengths (600, 800, and 1000 nm). In the best-case scenario, when the forward transmissivity is 85%, the backward transmissivity is 0.1%. Electromagnetic field profiles reveal that the designed diode strongly supports surface plasmons coupled across counterintuitive metal–dielectric pixel arrays. Thereby, it yields the transmission of first-order diffracted light with a high amplitude. In contrast, backward transmission has decoupled surface plasmons that redirect Poynting vectors back to the incident medium, resulting in near attenuation of its transmission. In addition, we experimentally verify the optical isolation function of the optical diode.

Elastomer cholesteric waveguide slab for a transverse elongation

ABSTRACT In this work, electromagnetic propagating modes within a planar waveguide featuring a cholesteric elastomer core whose helical axis is oriented perpendicular to the planar boundaries are analysed. The Maxwell equations and the constitutive equation are used to establish a novel configuration, enabling the tuning of mechanical stress through elastic strain in the perpendicular stretching along the helix axis. The derived set of equations is numerically solved, presuming the waveguide to be surrounded by either air or a vacuum medium. The corresponding band structure and the ratio between electric and magnetic modes have been plotted as a function of angular frequency. The amplitudes of the electromagnetic field profiles are also investigated as functions of position. The ratio of Transverse Electric and Transverse Magnetic modes, along with the cut-off frequencies, is also examined as functions of strain. Finally, the mixing of transverse electric and magnetic modes to generate new eigenmodes, as well as the investigation of their propagation conditions within the waveguide, is examined in this study.

Polynomial expansion method for full wave three-dimensional analysis of dielectric waveguides and periodic structures

In summary, the utilization of Legendre polynomial expansion in the modal analysis of stratified dielectric layers with doubly periodic permittivity profiles offers a departure from conventional methods. This novel approach, grounded in the analytical projection of Maxwell’s equations onto the Hilbert space defined by Legendre polynomials, results in well-behaved algebraic equations. These equations, in turn, facilitate the derivation of propagation constants and electromagnetic field profiles, circumventing issues related to numerical instability and oscillatory behavior. Moreover, the method's adaptability to extend its application to nonperiodic dielectric waveguides through the periodic repetition concept further underscores its versatility and potential impact in electromagnetic field analysis. Finally, to validate the proposed method, we conducted a comparative analysis of three standard test cases against previously reported results in the literature. The comparison showcased a high level of agreement, affirming the accuracy and efficacy of the presented approach.

Metabolomics comparison of metabolites and functional pathways in the SH-SY5Y cell model of Parkinson's disease under PEMF exposure

ObjectivePEMF is an emerging technique in the treatment of Parkinson's disease (PD) due to its potential improvement of movement speed. The aim of this study was to investigate the metabolic profiles of pulsed electromagnetic fields (PEMFs) in an SH-SY5Y cell model of PD. MethodsThe SH-SY5Y cell model of PD was induced by 1-methyl-4-phenylpyridinium (MPP+). Liquid chromatography mass spectrometry (LC‒MS)-based untargeted metabolomics was performed to examine changes in the PD cell model with or without PEMF exposure. We conducted KEGG pathway enrichment analysis to explore the potentially related pathways of the differentially expressed metabolites. ResultsA total of 275 metabolites were annotated, and 27 significantly different metabolites were found between the PEMF treatment and control groups (VIP >1, P < 0.05), mainly including 4 amino acids and peptides, 4 fatty acid esters, 2 glycerophosphoethanolamines, 2 ceramides and 2 monoradylglycerols; among them, 12 metabolites were upregulated, and 15 were downregulated. The increased expression levels of glutamine, adenosine monophosphate and taurine were highly associated with PEMF stimulation in the PD model. The enrichment results of differentially abundant metabolite functional pathways showed that biological processes such as the mTOR signaling pathway, PI3K-Akt signaling pathway, and cAMP signaling pathway were significantly affected. ConclusionPEMFs affected glutamine, adenosine monophosphate and taurine as well as their functional pathways in an in vitro model of PD. Further functional studies regarding the biological effect of these changes are required to evaluate the clinical efficacy and safety of PEMF treatment in PD.

Electromagnetic Field (EMF) Profile and Baselines at a Non- Haunted Control Location

There has been little to no environmental and experience data collected at randomlyselected non-haunted control sites despite the call for researchers and field investigatorsto do so over twenty years ago. Electromagnetic Fields (EMFs) and their associationand correlation with haunted locations and haunt-type phenomena have been studiedby both academics and hobbyist ghost hunters/paranormal investigators. The field hasprogressed over the years with mixed results and some within site controls. However,there is still a lack of data collected at non-haunted control locations, and many questionsremain on how to collect and analyze baseline data. The current study was conducted tocollect multi-hour multiple-run baseline EMF data to explore EMF profiles and to betterunderstand how EMF readings can vary temporally across a 3-axis EMF meter at a nonhauntedcontrol site. Results showed that a non-haunted control site had complex timevaryingmagnetic fields during long-term data collection periods at various days andtimes, similar to locations deemed to be anomalous. Limitations of the study are noted,and future research is suggested.

One-dimensional and two-dimensional Er3+-doped germanate glass waveguides by combination of He+ ion implantation and precise diamond blade dicing

Compact and miniaturized Er3+-doped waveguide structure is an important research direction in integrated optics. In this work, the Er3+-doped germanate glass was bombarded by a 400-keV He+ ion beam with a fluence of 6.0 × 1016 ions/cm2 for the formation of the one-dimensional waveguide in a vacuum. Subsequently, the precise diamond blade with a rotating velocity of 20,000 rpm and a cutting speed of 0.1 mm/s was applied to dice the surface of the one-dimensional waveguide for the fabrication of the two-dimensional structure. The formation mechanism and the refractive index profile of the one-dimensional waveguide were studied by the SRIM 2013 and the RCM, respectively. The electromagnetic field profiles for the fundamental modes of both one-dimensional and two-dimensional waveguides were measured by the end-face coupling method. It presents some useful information in the field of fabrication and characterization of optical waveguides for active photonic applications.

Deep learning-enhanced, open-source eigenmode expansion.

We present an open-source eigenmode expansion (EME) software package entirely implemented in the Python programming language. Eigenmode expansion Python (EMEPy) utilizes artificial neural networks to reproduce electromagnetic eigenmode field profiles to accelerate the EME process by a factor of 3. EMEPy provides an intuitive scripting interface, is easily compatible with a number of other Python packages, and is useful for educators and new designers.

Angular Interrogation-Based Self-Referenced LMR Sensor With High Sensitivity and High Figure of Merit

In this letter, we present the first report on self-referenced lossy mode resonance (LMR) based refractive index (RI) sensor, which operates in angular interrogation scheme. The proposed design consists of a coating of ITO over a silica prism which is further coated by Teflon and ITO films. The proposed design was optimized for the best performance of the sensor and therefore the thickness of the ITO and Teflon layers were optimized for TE and TM polarization of light. For the TM polarization, the highest sensitivity and figure of merit (FOM) are 93.01°/RIU and 845.50 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> respectively and for TE mode, the highest sensitivity and FOM are 83.74°/RIU and 322.10 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> , respectively around 1.38 RI of analyte medium. To explain the sensing and self-referenced mechanisms, the electromagnetic (EM) field profiles were plotted using COMSOL which helps one understand the working of the sensor.

Improving image quality in transcranial magnetic resonance guided focused ultrasound using a conductive screen

Transcranial Magnetic Resonance guided Focused Ultrasound (TcMRgFUS) has been proven to be an effective treatment for some neurological disorders such as essential and Parkinson's tremor. However, magnetic resonance guidance at 3 Tesla (3T) frequencies and using the large hemispherical transducers required for TcMRgFUS results in artifactual low-signal bands that pass through key regions of the brain. The purpose of this work was to investigate the use of a circular conductive Radio Frequency (RF) screen, that is bent to have a 12 cm radius in one direction and positioned near the top or back of the head, to reduce or remove these artifactual low-signal bands in TcMRgFUS.The impact of using an RF screen to remove these low signal bands was studied in both imaging experiments and electromagnetic simulations. Hydrophone measurements of the acoustic transparency of the bronze 2 mm diameter square mesh screen used in the imaging studies were compared with temperature measurements with and without the screen in heating studies in the TcMRgFUS system.The imaging and simulation studies both show that for the different screen configurations studied in this work, RF screen removes the low-signal bands and increases both homogeneity and signal-to-noise ratio (SNR) throughout the region of the brain. Hydrophone and heating studies indicate that even a 2 mm wire mesh provides minimal attenuation to the ultrasound beam. Simulation results also suggest that a 1 cm mesh will provide adequate artifact suppression with even less ultrasound attenuation.An RF screen that disrupts the natural waveguide nature of the transducer in the 3T MR environment can change the electromagnetic field profile to reduce unwanted artifacts and provide an imaging region which has more homogeneity and higher SNR throughout the brain.

Detection of electron spin resonance down to 10 K using localized spoof surface plasmon

In this study, novel use of the electromagnetic field profile of a localized spoof surface plasmonic mode to detect electron spin resonance (ESR) is being reported. The mode is supported on a resonator with a complementary metallic spiral structure, etched on the ground plane of a microstrip line having a characteristic impedance of 50 Ω. The change in characteristics of the mode of interest with lowering of temperature has been observed and analyzed. ESR spectra of three paramagnetic samples—2,2-diphenyl-1-picrylhydrazyl (DPPH), galvinoxyl, and 2,2,6,6-tetramethylpiperidine-1-oxyl are recorded using this resonator at room temperature. ESR spectra of DPPH are also captured down to 10 K. Potential application of the mode in the detection of microwave induced Rashba field-driven ESR has been discussed.

Mid-Range Wireless Power Transfer at 100 MHz Using Magnetically Coupled Loop-Gap Resonators

We describe efficient four-coil inductive power transfer (IPT) systems that operate at 100 MHz. The magnetically-coupled transmitter and receiver were made from electrically-small and high-Q loop-gap resonators (LGRs). In contrast to the commonly-used helical and spiral resonators, the LGR design has the distinct advantage that electric fields are strongly confined to the capacitive gap of the resonator. With negligible fringing electric fields in the surrounding space, the IPT system is immune to interference from nearby dielectric objects, even when they are in close proximity to the transmitter and/or receiver. We experimented with both cylindrical and split-toroidal LGR geometries. Although both systems performed well under laboratory conditions, the toroidal geometry has the additional advantage that the magnetic flux is weak everywhere except within the bore of the LGR and in the space directly between the transmitter and receiver. Furthermore, we show that the toroidal LGR system can be operated efficiently at a fixed frequency for a wide range of transmitter-receiver distances. The experimental results are complimented by 3-D finite-element simulations which were used to investigate the electromagnetic field profiles and surface current density distributions. Finally, we demonstrate the use of our IPT system at powers up to 32 W and discuss possible applications.

Helical Magnetic Cavities: Kinetic Model and Comparison With MMS Observations

AbstractMagnetic cavities are sudden depressions of magnetic field strength widely observed in the space plasma environments, which are often accompanied by plasma density and pressure enhancement. To describe these cavities, self‐consistent kinetic models have been proposed as equilibrium solutions to the Vlasov‐Maxwell equations. However, observations from the Magnetospheric Multi‐Scale (MMS) constellation have shown the existence of helical magnetic cavities characterized by the presence of azimuthal magnetic field, which could not be reconstructed by the aforementioned models. Here, we take into account another invariant of motion, the canonical axial momentum, to construct the particle distributions and accordingly modify the equilibrium model. The reconstructed magnetic cavity shows excellent agreement with the MMS1 observations not only in the electromagnetic field and plasma moment profiles but also in electron pitch‐angle distributions. With the same set of parameters, the model also predicts signatures of the neighboring MMS3 spacecraft, matching its observations satisfactorily.

3D super-resolved imaging in live cells using sub-diffractive plasmonic localization of hybrid nanopillar arrays

Abstract Analysing dynamics of a single biomolecule using high-resolution imaging techniques has been had significant attentions to understand complex biological system. Among the many approaches, vertical nanopillar arrays in contact with the inside of cells have been reported as a one of useful imaging applications since an observation volume can be confined down to few-tens nanometre theoretically. However, the nanopillars experimentally are not able to obtain super-resolution imaging because their evanescent waves generate a high optical loss and a low signal-to-noise ratio. Also, conventional nanopillars have a limitation to yield 3D information because they do not concern field localization in z-axis. Here, we developed novel hybrid nanopillar arrays (HNPs) that consist of SiO2 nanopillars terminated with gold nanodisks, allowing extreme light localization. The electromagnetic field profiles of HNPs are obtained through simulations and imaging resolution of cell membrane and biomolecules in living cells are tested using one-photon and 3D multiphoton fluorescence microscopy, respectively. Consequently, HNPs present approximately 25 times enhanced intensity compared to controls and obtained an axial and lateral resolution of 110 and 210 nm of the intensities of fluorophores conjugated with biomolecules transported in living cells. These structures can be a great platform to analyse complex intracellular environment.

Simulation studies on microwave-assisted pyrolysis of biomass for bioenergy production with special attention on waveguide number and location

The society’s concern has moved toward sustainability nowadays and hence, the conversion of biomass into biofuels, through pyrolysis process, is one of the current research trends. Green processing technologies, like microwave heating, has been suggested to replace the conventional heating for biomass conversion as it provides energy-efficient heating and reduces time consumption. In this work, COMSOL Multiphysics software was used to study the effects of the waveguide position (bottom-fed vs side-fed) and unit (single-fed vs double-fed) on the electromagnetic field and heat distribution profile within the sample. Based on the results, the double-fed microwave can achieve higher maximum temperature (462 °C) at the same simulation time, followed by the single bottom-fed reactor (404 °C). An extension to the investigated work with more than two waveguides has shown that it will neither improve the electric field distribution nor increase the maximum temperature. This work concludes that both the position and unit of the waveguide are highly influential factors in determining the quality and speed of the biomass heating process. The double-fed microwave is the most suitable design to accelerate the pyrolysis process. The assumption of this simulation study is further validated as there is only ∼5% difference between simulations and experiments.

Slow light with interleaved p-n junction to enhance performance of integrated Mach-Zehnder silicon modulators

Abstract Slow light is a very important concept in nanophotonics, especially in the context of photonic crystals. In this work, we apply our previous design of band-edge slow light in silicon waveguide gratings [M. Passoni et al, Opt. Express 26, 8470 (2018)] to Mach-Zehnder modulators based on the plasma dispersion effect. The key idea is to employ an interleaved p-n junction with the same periodicity as the grating, in order to achieve optimal matching between the electromagnetic field profile and the depletion regions of the p-n junction. The resulting modulation efficiency is strongly improved as compared to common modulators based on normal rib waveguides, even in a bandwidth of 20–30 nm near the band edge, while the total insertion loss due to free carriers is not increased. The present concept is promising in view of realizing slow-light modulators for silicon photonics with reduced energy dissipation.

Observation of asymmetric electromagnetic field profiles in chiral metamaterials

We experimentally observe asymmetric electromagnetic field profiles along two-dimensional chiral metamaterials. The asymmetric field profiles depending on the chirality and the operation frequency have been reproduced well by the numerical simulation. Around a chiral meta-atom, distribution of a Poynting vector is found to be shifted asymmetrically. These results are explained in terms of an analogy with the side-jump mechanism in the electronic anomalous Hall systems.

Role of interactions in the magneto-plasmonic response at the geometrical threshold of surface continuity

The optical and magneto-optical behavior in periodically nanostructured surfaces at the threshold of surface continuity is revealed. We address Co films that evolve from an island-like array to a connecting network of islands that form a membrane pattern. The analysis of magneto-optical spectra as well as numerical simulations show significant differences between continuous and broken membranes that depend dramatically on the energy of the incoming radiation. Light localization increases the magneto-optical signal in the membranes. However, the generation of hot spots is not accompanied with magneto-optic enhancement. The electromagnetic field profile within the membrane system can explain the differences in the transmission and in the magneto-optic Kerr signal.

Two-dimensional fivefold photonic crystal microcavity

Fivefold photonic crystal (PC) structure is originally presented with theoretical investigation about its photonic band gap through transmission spectrum calculated by finite-difference time-domain methods. The existence of PC band gap makes it possible for defect structures with high-quality factor. Two types of fivefold PC microcavity are proposed of which the quality factor, normalized frequency, and electromagnetic field profile have been simulated. With some preliminary structural parameters optimization, monopole mode in one-defect fivefold PC microcavity with a high-Q factor (∼2212) and whispering gallery mode in six-defect fivefold PC microcavity with a high-Q factor (∼13,300) are obtained.

Effect of gas mixing on physical properties of warm collisional helicon plasmas

The effect of inert gas mixing on the physical properties of a helicon plasma source with a Nagoya type III antenna is analytically investigated by taking into account the thermal and collisional effects. The dielectric permittivity tensor of this mixed gas plasma is obtained by using the Bhatnagar–Gross– Krook kinetic theory. Considering the dielectric tensor of mixed gas plasma and solving the electromagnetic field equations, the profiles of electromagnetic fields and plasma resistance are plotted and discussed. The results show that the plasma resistance peaks decrease with increasing Xe fraction in Ar–Xe plasma, and increase with the He fraction in Ar–He plasma. It is also shown that by increasing the xenon filling fraction, the electromagnetic field amplitudes are lowered, and by increasing the helium filling fraction, they are increased.