Free Electron Research Articles

Cascaded nanocavity-shaped metasurfaces for realizing an intensive radiation absorption in the mid-to-long infrared region based on electromagnetic wavefield resonance response and accumulation

A type of cascaded metal-insulator-metal nanocavity-shaped (CMNM) metasurface has been developed for realizing an intensive radiation absorption in the mid-to-long infrared (IR) region. The radiation absorption characteristics are analyzed according to the impedance matching mechanism. By evaluating the electromagnetic wavefield properties at several wavelength points selected, the spatial resonance morphology of the electric field and magnetic field components excited mainly by the resonance of the free electrons over the surfaces of the metasurface are simulated effectively. The stimulating and redistributing behaviors of the conductive electric-currents, including the surface equivalent eddy-currents surrounding a couple of dielectric films configurated in the cascaded nanocavities, and the net charges distributed over three Ti films, which will induce a resonant accumulation enhancement of the wavefields in the metasurfaces corresponding to the incident IR radiation, are exhibited. An average absorption level of more than 85% in the 3–14µm wavelength region is already achieved. Due to the IR responding and manipulating approaches proposed by us, the CMNM samples also exhibit an insensitivity of the beam incident angle for some typical applications in uncooled infrared imaging and thermal radiation detection.

Temperature Dependence of the Sensitivity of PVDF Pyroelectric Sensors to THz Radiation: Towards Cryogenic Applications.

The application of terahertz (THz) science in industrial technology and scientific research requires efficient THz detectors. Such detectors should be able to operate under various external conditions and conform to existing geometric constraints in the required application. Pyroelectric THz detectors are among the best candidates. This is due to their versatility, outstanding performance, ease of fabrication, and robustness. In this paper, we propose a compact pyroelectric detector based on a bioriented poled polyvinylidene difluoride film coated with sputtered metal electrodes for in situ absorption measurement at cryogenic temperature. The detector design was optimized for the registration system of the electron paramagnetic resonance (EPR) endstation of the Novosibirsk Free Electron Laser facility. Measurements of the detector response to pulsed THz radiation at different temperatures and electrode materials showed that the response varies with both the temperature and the type of electrode material used. The maximum signal level corresponds to the temperature range of 10-40 K, in which the pyroelectric coefficient of the PVDF film also has a maximum value. Among the three coatings studied, namely indium tin oxide (ITO), Au, and Cu/Ni, the latter has the highest increase in sensitivity at low temperature. The possibility of using the detectors for in situ absorption measurement was exemplified using two typical molecular spin systems, which exhibited a transparency of 20-30% at 76.9 cm-1 and 5 K. Such measurements, carried out directly in the cryostat with the main recording system and sample fully configured, allow precise control of the THz radiation parameters at the EPR endstation.

Spatiotemporal dynamics of fast electron heating in solid-density matter via XFEL

High-intensity, short-pulse lasers are crucial for generating energetic electrons that produce high-energy-density (HED) states in matter, offering potential applications in igniting dense fusion fuels for fast ignition laser fusion. High-density targets heated by these electrons exhibit spatially non-uniform and highly transient conditions, which have been challenging to characterize due to limitations in diagnostics that provide simultaneous high spatial and temporal resolution. Here, we employ an X-ray Free Electron Laser (XFEL) to achieve spatiotemporally resolved measurements at sub-micron and femtosecond scales on a solid-density copper foil heated by laser-driven fast electrons. Our X-ray transmission imaging reveals the formation of a solid-density hot plasma localized to the laser spot size, surrounded by Fermi degenerate, warm dense matter within a picosecond, and the energy relaxation occurring within the hot plasma over tens of picoseconds. These results validate 2D particle-in-cell simulations incorporating atomic processes and provide insights into the energy transfer mechanisms beyond current simulation capabilities. This work significantly advances our understanding of rapid fast electron heating and energy relaxation in solid-density matter, serving as a key stepping stone towards efficient high-density plasma heating and furthering the fields of HED science and inertial fusion energy research using intense, short-pulse lasers.

Complex anisotropy ratio of third harmonic generation in a semiconductor using a terahertz free electron laser.

The nonlinear susceptibility in the terahertz region is expected to have a non-negligible imaginary part originating from the momentum-dependent scattering time of free carriers, but it has been scarcely reported. By utilizing an intense 4 THz beam from a terahertz free electron laser, we investigated the azimuth angle dependence of the third harmonic generation (THG) from semiconductors. The observed angular anisotropy of THG revealed the contribution of the imaginary part of the nonlinear susceptibility originating from the momentum-scattering time relation in addition to its real part originating from the band nonparabolicity. The results provide a deeper understanding of nonlinear optics in the terahertz region.

Generation of Quantum Vortex Electrons with Intense Laser Pulses.

Accelerating a free electron to high-energy forms the basis for studying particle and nuclear physics. Here it is shown that the wave function of such an energetic electron can be further manipulated with the femtosecond intense lasers. During the scattering between a high-energy electron and a circularly polarized laser pulse, a regime is found where the enormous spin angular momenta of laser photons can be efficiently transferred to the electron orbital angular momentum (OAM). The wave function of the scattered electron is twisted from its initial plane-wave state to the quantum vortex state. Nonlinear quantum electrodynamics (QED) theory suggests that the GeV-level electrons acquire average intrinsic OAM beyond at laser intensities of 1020Wcm-2 with linear scaling. These electrons emit γ-photons with two-peak spectrum, which sets them apart from the ordinary electrons. The findings demonstrate a proficient method for generating relativistic leptons with the vortex wave functions based on existing laser technology, thereby fostering a novel source for particle and nuclear physics.

Plasmonic Radiation from Spin-Momentum Locking.

Chiral light emission plays a key role in sensing, tomography, quantum communication, among others. Whereas, achieving highly pure, tunable chirality emission across a broad spectrum currently presents significant challenges. Free-electron radiation emerges as a promising solution to surpass these barriers, especially in hard-to-reach regimes. Here, chiral free-electron radiation is presented by exploiting the spin-momentum locking (SML) property of spoof surface plasmons (SSPs). When the phase velocity of free electrons matches that of the SSPs, the SSPs can be excited. By implementing wavenumber compensation through perturbations, the confined SSPs are transformed into free-space free-electron radiation. Owing to the law of angular momentum conservation, this process converts the transverse spin angular momentum of SSPs into the longitudinal spin angular momentum of free-electron radiation during the process, producing pure, tunable, and chiral free-electron radiation across a broad spectrum. This method achieves an optimal degree of circular polarization approaching -1. The innovative methodology can be adapted to SML-enabled guided states or silicon photonics platforms, offering new avenues for achieving chiral emission.

Evolution from ultrafast demagnetization to magnetization reversal at the Fe sites in Gd23Fe67Co10 with laser fluence, observed by the element-selective magneto-optical Kerr effect using an X-ray free electron laser

In the present study, we investigated the magnetization dynamics of a Gd23Fe67Co10 nanofilm. We subjected the nanofilm to a time-resolved experiment to examine its magneto-optical effect using an X-ray free electron laser. By tuning the energy of the photons to the core-level resonance of the Fe absorption edge, we selectively determined the magnetic behavior of the elements at the Fe site in the nanofilm. When triggered by an ultrashort pulse of infrared radiation, the materials underwent demagnetization and magnetic reversal, depending on fluence of the laser. The following relaxation process was found to be associated not only with the fast recursion but also with a long sustention of the reversed magnetization. The experimental observation consistently match with the recent prediction by the magnetic dynamic simulation. The ultrafast dynamics was triggered by the ultrafast thermal effect and it was recovered toward the initial state in the non-thermal manner.

Effect of multi-temperature models on heat transfer and electron behavior in hypersonic flows

In hypersonic computational fluid dynamics, the two-temperature (2-T) model is widely used to simulate thermochemical nonequilibrium. The 2-T model incorporates translational-rotational and electron-electronic-vibrational energies, assuming that the integrated energies have the equivalent temperature. In this study, multi-T models are constructed to accurately predict the effects on heat flux and free electrons due to the separation of energy modes under hypersonic environments. The three-temperature (3-T) model separates the electron-electronic energy from the electron-electronic-vibrational energy of the 2-T model. The 3-T model can accurately predict the distribution and temperature of free electrons by separating the energy of free electrons, which has different characteristics from heavy particles. The four-temperature model treats rotational energy as a nonequilibrium energy mode, distinct from translational-rotational energy. While the rotational temperature reaches equilibrium rapidly at low temperatures, at high-temperature regime rotational temperature shows a relaxation time similar to that of vibrational temperature, which cannot be ignored. To develop multi-T models, electron-vibrational relaxation and translational-rotational relaxation, which are omitted in the 2-T model, are considered. Various flight test and ground facility conditions are analyzed to verify the effects of electron and heat flux under circumstances that include shock, expansion, and shock wave boundary layer interaction. The results of the multi-T models show significant differences in electron temperature and distribution caused by electron-electronic nonequilibrium. Additionally, rotational nonequilibrium increases the shock standoff distance and alters the electron distribution at high altitudes. The heat flux difference across multi-T models is found to be negligible, except in the high degree of ionization condition.

Objects May Be Closer than They Appear: Significant Host Galaxy Dispersion Measures of Fast Radio Bursts in Zoom-in Simulations

We investigate the contribution of host galaxies to the overall dispersion measures (DMs) for fast radio bursts (FRBs) using the Feedback in Realistic Environments (FIRE-2) cosmological zoom-in simulation suite. We calculate DMs from every star particle in the simulated L* galaxies by ray-tracing through their multiphase interstellar medium, summing the line-of-sight free thermal electron column for all gas elements within ±20 kpc of the galactic midplane. At z = 0, we find average (median) host-galaxy DMs of 74 (43) and 210 (94) pc cm−3 for older (≳10 Myr) and younger (≲10 Myr) stellar populations, respectively. Inclination raises the median DM measured for older populations (≳10 Myr) in the simulations by a factor of ∼2 but generally does not affect the younger stars deeply embedded in H ii regions except in extreme edge-on cases (inclination ≳85°). In kinematically disturbed snapshots (z = 1 in FIRE), the average (median) host-galaxy DMs are higher: 80 (107) and 266 (795) pc cm−3 for older (≳10 Myr) and younger (≲10 Myr) stellar populations, respectively. FIRE galaxies tend to have higher DM values than cosmological simulations such as IllustrisTNG, with larger tails in their distributions to high DMs. As a result, FRB host galaxies may be closer (lower redshift) than previously inferred. Furthermore, constraining host-galaxy DM distributions may help significantly constrain FRB progenitor models.

Total free-free Gaunt factors prediction using machine learning models

Gaunt factors are fundamental in describing the interaction of free electrons with photons, playing a crucial role in astrophysical processes such as radiation transport and emission spectra. Traditional methods for computing Gaunt factors involve complex integrations and intricate mathematical formulations, often being computationally expensive and time-consuming. This study explores an alternative approach using machine learning models to predict free-free Gaunt factors. Three models were employed: Artificial Neural Network (ANN), Support Vector Regression (SVR), and Gradient Boosting Regression (GBR). The obtained results demonstrate high performance, with R 2 scores ranging from 0.98 to 0.99, indicating the potential of machine learning models to accurately predict Gaunt factors.

Investigation of the Abraham–Minkowski dilemma in Smith–Purcell radiation from photonic crystals

The debate over whether light’s momentum within a medium is accurately described by Abraham or Minkowski formulation has persisted for over a century. To our knowledge, this dilemma has not been explored within the context of Smith–Purcell radiation. This is because, in conventional Smith–Purcell radiation scenarios, the refractive index is equal to one, leading both the Abraham and Minkowski formulations to yield identical results. Here, we investigate the Abraham–Minkowski dilemma within the realm of Smith–Purcell radiation from photonic crystals, where the refractive index deviates from one. In particular, we find that 3 MeV free electrons impinge a photonic crystal with a grating length of 2.1 μm, resulting in the emission of red light when analyzed based on Abraham’s momentum and blue light when analyzed based on Minkowski’s momentum. In addition, our findings reveal that the disparity in wavelength as predicted by Abraham’s momentum and Minkowski’s momentum depends on the grating length and the refractive index. Our findings offer a method to address the Abraham–Minkowski dilemma within the context of Smith–Purcell radiation, thereby enhancing our understanding of both the Abraham–Minkowski dilemma and Smith–Purcell radiation.

What is the Reason That the Pharmacological Future of Chemotherapeutics in the Treatment of Lung Cancer Could Be Most Closely Related to Nanostructures? Platinum Drugs in Therapy of Non-Small and Small Cell Lung Cancer and Their Unexpected, Possible Interactions. The Review.

Over the course of several decades, anticancer treatment with chemotherapy drugs for lung cancer has not changed significantly. Unfortunately, this treatment prolongs the patient's life only by a few months, causing many side effects in the human body. It has also been proven that drugs such as Cisplatin, Carboplatin, Oxaliplatin and others can react with other substances containing an aromatic ring in which the nitrogen atom has a free electron group in its structure. Thus, such structures may have a competitive effect on the nucleobases of DNA. Therefore, scientists are looking not only for new drugs, but also for new alternative ways of delivering the drug to the cancer site. Nanotechnology seems to be a great hope in this matter. Creating a new nanomedicine would reduce the dose of the drug to an absolute minimum, and thus limit the toxic effect of the drug; it would allow for the exclusion of interactions with competitive compounds with astructuresimilar to nucleobases; it would also permit using the so-called targeted treatment and bypassing healthy cells; itwouldallow for the introduction of other treatment options, such as radiotherapy directly to the cancer site; and it would provide diagnostic possibilities. This article is a review that aims to systematize the knowledge regarding the anticancer treatment of lung cancer, but not only. It shows the clear possibility of interactions of chemotherapeutics with compounds competitive to the nitrogenous bases of DNA.It also shows the possibilities of using nanostructures as potential Platinum drug carriers, and proves that nanomedicine can easily become a new medicinal product in personalized medicine.

Comprehensive characterization of nitrogen-related defect states in β-Ga2O3 using quantitative optical and thermal defect spectroscopy methods

This study provides a comprehensive analysis of the dominant deep acceptor level in nitrogen-doped beta-phase gallium oxide (β-Ga2O3), elucidating and reconciling the hole emission features observed in deep-level optical spectroscopy (DLOS). The unique behavior of this defect, coupled with its small optical cross section, complicates trap concentration analysis using DLOS, which is essential for defect characterization in β-Ga2O3. A complex feature arises in DLOS results due to simultaneous electron emission to the conduction band and hole emission to the valence band from the same defect state, indicating the formation of two distinct atomic configurations and suggesting metastable defect characteristics. This study discusses the implications of this behavior on DLOS analysis and employs advanced spectroscopy techniques such as double-beam DLOS and optical isothermal measurements to address these complications. The double-beam DLOS method reveals a distinct hole emission process at EV+1.3 eV previously obscured in conventional DLOS. Optical isothermal measurements further characterize this energy level, appearing only in N-doped β-Ga2O3. This enables an estimate of the β-Ga2O3 hole effective mass by analyzing temperature-dependent carrier emission rates. This work highlights the impact of partial trap-filling behavior on DLOS analysis and identifies the presence of hole trapping and emission in β-Ga2O3. Although N-doping is ideal for creating semi-insulating material through the efficient compensation of free electrons, this study also reveals a significant hole emission and migration process within the weak electric fields of the Schottky diode depletion region.

New 511 keV Line Data Provide Strongest sub-GeV Dark Matter Constraints

We explore the 511 keV emission associated with sub-GeV dark matter (DM) particles that can produce electron–positron pairs and form positronium after thermalizing. We use ∼16 yr of data from the Spectrometer on INTEGRAL to constrain DM properties, including the full positron propagation and losses, and the suppression of free electron density away from the Galactic plane. We show that the predicted longitude and latitude profiles vary significantly for different DM masses, unlike previous assumptions, and obtain the strongest limits on sub-GeV DM (from the MeV to a few GeV) so far, excluding cross sections down to 〈σ v〉 ≲ 10−32 cm3 s−1 for m χ ∼ 1 MeV and 〈σ v〉 ≲ 10−26 cm3 s−1 for m χ ∼ 5 GeV and lifetimes up to τ ≳ 1029 s for m χ ∼ 1 MeV and τ ≳ 1027 s for m χ ∼ 5 GeV for the typical Navarro–Frenk–White DM profile. Our derived limits are robust within a factor of a few due to systematic uncertainties.

High-Performance Sensing Platform Based on Morphology/Lattice Collaborative Control of Femtosecond-Laser-Induced MXene-Composited Graphene.

Flexible sensors based on laser-induced graphene (LIG) are widely used in wearable personal devices, with the morphology and lattice arrangement of LIG the key factors affecting their performance in various applications. In this study, femtosecond-laser-induced MXene-composited graphene (LIMG) is used to improve the electrical conductivity of graphene by incorporating MXene, a 2D material with a high concentration of free electrons, into the LIG structure. By combining pump-probe detection, laser-induced breakdown spectroscopy (LIBS), and density functional theory (DFT) calculations, the morphogenesis and lattice structuring principles of LIMG is explored, with the results indicating that MXene materials are successfully embedded in the graphene lattice, altering both their morphology and electrical properties. The structural sparsity and electrical conductivity of LIMG composites (up to 3187 Sm-1) are significantly enhanced compared to those of LIG. Based on these findings, LIMG has been used in wearable electronics. LIMG electrodes are used to detect uric acid, with a minimum detection limit of 2.48µM. Additionally, LIMG-based pressure and bending sensors have been successfully used to monitor human limb movement and pulse. The direct in situ femtosecond laser patterning synthesis of LIMG has significant implications for developing flexible wearable electronic sensors.

Improving photosynthetic efficiency of rice via over-expressing a ferredoxin-like protein gene from Methanothermobacter thermautotrophicus.

Ferredoxins (Fds) are crucial in various essential plant metabolic processes, including photosynthesis, fermentation and aerobic nitrogen fixation, due to their role in electron transport rate (ETR). However, the full scope of ferredoxin's function across prokaryotes and eukaryotic plants remains less understood. This study investigated the effect of MtFd from Methanothermobacter thermoautotrophicus on rice photosynthetic efficiency. We found that MtFd was localized in the chloroplasts of rice protoplasts. Transgenic analysis showed that MtFd significantly enhanced the photosynthetic capacity compared to the wild-type plants. This enhancement was evident through increased ETR, NADPH content and net photosynthetic rates, as well as decreased non-photochemical quenching (NPQ). Despite similar biomass to wild type plants, MtFd transgenic plants exhibited a marked increase in grain size and the 1000-grian weight. The elevated ETR and surplus free electrons in transgenic plants result in a considerable rise in cellular ROS content, which in turn enhances the enzymatic activity of the antioxidant system. In summary, our findings suggest that introducing the Fd protein from M. thermoautotrophicus into transgenic rice improves photosynthetic efficiency by accelerating ETR, which triggers the cellular oxidative stress response.

Influence of γ-radiation on magnetoelectrical properties of Bi0.85Sb0.15 (0.001≤x≥0.05) solid solution

Abstract The influence of γ-quantum on the magnetoelectric properties of Bi0.85Sb0.15 <Pbx> (0.001≤x≥0.05) thermoelectrics doped with lead atoms at ~77÷300K and magnetic field induction up to 1.0 Tesla has been studied. It was found that at low doses of gamma irradiation of the Bi0.85Sb0.15 <Pb> solid solution, point defects are formed, which lead to an increase in the concentration of free electrons n, specific electrical conductivity σ and a decrease in the absolute value of the thermo EMF coefficients α and RH. As the dose of γ-quanta increases in the process of subsequent restructuring, point defects accumulate, i.e. accumulation of point defects, which leads to a decrease in the concentration of current carriers and a corresponding change in σ, α. and RH.

Coherent electron phase-space manipulation by combined elastic and inelastic light-electron scattering

Abstract Photon-Induced Near-field Electron Microscopy (PINEM), Kapitza-Dirac (KD) gratings, and ponderomotive phase plates are examples of techniques in which the wave function of an electron in free space is manipulated using light fields: Free Electron Quantum Optics (FEQO). These effects are usually treated in separate theoretical frameworks. In this paper we present a unified, two-pronged framework that can be used to describe and numerically evaluate the performance of a number of FEQO-based electron-optical elements. The first part is an extension of an existing analytical treatment of PINEM, based on solving a relativistically corrected Schrödinger equation. The extension covers both second-order contributions to PINEM and the Kapitza-Dirac effect. The second, novel element of the approach is based on electron wavefront reconstruction by evaluating the quantum mechanical phase along a bundle of classical electron trajectories. The quasi-classical (but fully relativistic) approach lends itself to simulating a wide variety of FEQO devices, including the examples mentioned. We apply both approaches to a few specific experimental configurations: mirror-based first-order PINEM, second-order PINEM in very high laser intensity, and Kapitza-Dirac diffraction. The results show excellent agreement between the analytical results and the quasi-classical simulations. Finally, we propose a setup that combines KD and PINEM to allow for simultaneous coherent energy and transverse momentum shaping of an electron beam, and present simulation results thereof.

Alter the charge transport orientation of aromatic polyimide by induction effect to achieve superior high-temperature capacitance performance

Aerospace, electric vehicles, and other particular application scenarios place higher demands on the applicable electric field and temperature of capacitors. Polyimide, as the most ideal and widely studied high-temperature capacitor dielectric material, has poor insulation performance under extreme conditions. The main reason is that many conjugated π-bonds on its aromatic rings provide channels for the movement of free electrons, this phenomenon is more intense in high-temperature and high-field environments, which accelerates the high-temperature performance degradation of polyimide. Herein, we propose a molecular structure strategy to design high-temperature capacitance performance polymer dielectrics based on the induction effect. Both the experimental and density functional theory calculation results indicate that the polar functional groups -CF3 and –OCH3 can lead to a strong induction effect, which changes the direction of electron transport on the aromatic ring, serve to weaken the free-sharing ability of electrons in the conjugated π bond, increases the energy levels of PI and induces the formation of local deep traps in the polymer films, which significantly restrains charge carrier transport, ultimately improves the high-temperature capacitance property for aromatic polyimide. The resultant polymer film exhibits an excellent discharged energy density (Ud) of 7.9 J/cm3 at 150 °C and 810.3 MV/m. Meanwhile, it maintains excellent stability at over 100,000 fatigue tests and 500 MV/m. Hopefully, it will provide theoretical and technical support for developing high-performance capacitors.

Electromagnetic Plasma Reactor: Fermionic Derivation Tools

From the developed theories around of an electromagnetic plasma reactor designed and controlled through geometrical invariants has been demonstrated the existence of derived products from electromagnetic plasma as are phonons, fermions, ions, free electrons and protons, magnetic and electric drifts, which can be used as complement or development part of the electromagnetic propulsion system where the fermion flow can produce a ionic force that could be used as propulsion force considering shock waves produced with an electric field on these ions. Likewise, experimentally and considering direct current and voltage in a constant regime, has been detected as ionic wind which carries fermion products to be used too in the possible electromagnetic propulsion. These are other products proposes of previous works. Likewise, through of a caption and detection camera, is measured the electromagnetic properties of the ionic flow of the space derived from the electromagnetic plasma, and is proposed a curvature energy signal of magnetic nature to measure the force and control the electromagnetic plasma and its ionic flow.