Strong Longitudinal Electric Field Research Articles

Relativistic Electrons from Vacuum Laser Acceleration Using Tightly Focused Radially Polarized Beams.

We generate a tabletop pulsed relativistic electron beam at 100Hz repetition rate from vacuum laser acceleration by tightly focusing a radially polarized beam into a low-density gas. We demonstrate that strong longitudinal electric fields at the focus can accelerate electrons up to 1.43MeV by using only 98GW of peak laser power. The electron energy is measured as a function of laser intensity and gas species, revealing a strong dependence on the atomic ionization dynamics. These experimental results are supported by numerical simulations of particle dynamics in a tightly focused configuration that take ionization into consideration. For the range of intensities considered, it is demonstrated that atoms with higher atomic numbers like krypton can favorably inject electrons at the peak of the laser field, resulting in higher energies and an efficient acceleration mechanism that reaches a significant fraction (≈14%) of the theoretical energy gain limit.

Positron Generation and Acceleration in a Self-Organized Photon Collider Enabled by an Ultraintense Laser Pulse.

We discovered a simple regime where a near-critical plasma irradiated by a laser of experimentally available intensity can self-organize to produce positrons and accelerate them to ultrarelativistic energies. The laser pulse piles up electrons at its leading edge, producing a strong longitudinal plasma electric field. The field creates a moving gamma-ray collider that generates positrons via the linear Breit-Wheeler process-annihilation of two gamma rays into an electron-positron pair. At the same time, the plasma field, rather than the laser, serves as an accelerator for the positrons. The discovery of positron acceleration was enabled by a first-of-its-kind kinetic simulation that generates pairs via photon-photon collisions. Using available laser intensities of 10^{22} W/cm^{2}, the discovered regime can generate a GeV positron beam with a divergence angle of around 10° and a total charge of 0.1pC. The result paves the way to experimental observation of the linear Breit-Wheeler process and to applications requiring positron beams.

Focusing of Radially Polarized Electromagnetic Waves by a Parabolic Mirror

It is well-known that a strong longitudinal electric field and a small spot size are observed when radially polarized beams are tightly focused using a high numerical aperture parabolic mirror. The longitudinal electric field component can accelerate electrons along the propagation axis at high intensities in the focal region, which opens an application in particle acceleration. In this paper, we present a rigorous derivation of the electric field obtained when a radially polarized, monochromatic, flat-top beam is focused by a parabolic mirror. The formulae were deduced from the Stratton–Chu integral known from vector diffraction theory. We examined the influence of the focusing parameters on the distribution of both the longitudinal and radial electric field components. In the small numerical aperture and short wavelength regimes, excellent agreement was found with the results obtained from the Rayleigh–Sommerfeld formula. The calculation method can be adapted for various beam types and for electromagnetic pulses as well.

Relativistic electron bunches accelerated by radially polarized TW lasers from near-critical-density plasmas

By three-dimensional particle-in-cell simulation, we study electron acceleration by tightly focusing a few-cycle radially polarized laser onto near-critical-density plasmas. Laser ponderomotive force first pushes electrons into the target, forming a compressed electron layer and leaving behind a charge-separation field. Together with the strong longitudinal electric field of this radially polarized light, the charge-separation field accelerates the electrons backward and injects them into laser fields. The reflected light continuously accelerates these injected electrons by its longitudinal field. Simulations show that a tight quasi-monoenergetic electron bunch at 15 MeV is generated within a few micrometers.

High-energy proton beam acceleration driven by an intense ultrarelativistic electron beam in plasma

We report a generation of energetic protons by the interaction of a high-energy electron driving beam with an underdense plasma slab. After an interaction period of approximately 4000 fs, a proton beam with maximum energy greater than 250 MeV can be achieved by applying a driving beam with energy 1.0 GeV to a 200 $\mathrm {\mu }$ m plasma slab. Our two-dimensional particle-in-cell simulations also show that the proton acceleration process can be divided into two stages. In the first stage, a strong positive longitudinal electric field appears near the rear boundary of the plasma slab after the driving beam has passed through it. This acceleration process is similar to the target normal sheath acceleration scheme by the interaction between intense pulsed laser with overdense plasma targets. In the second stage, the accelerated protons experience a long-range acceleration process with a two-stream instability between the high-energy driving beam and the proton beam. Further analyses show that this accelerated proton beam is equipped with the property of good collimation and high energy. This scheme presents a new way for proton or ion acceleration on some special occasions.

Resistive switching effect in the n-InGaAs/GaAs heterostructures with double tunnel-coupled quantum wells

The electric conductivity behavior in the single and double tunnel-coupled quantum wells (QW) with different doping profile caused by the impact of short pulses of the strong longitudinal (in the quantum wells plane) electric field has been investigated. It is established that at low temperatures (4 K) after such an impact the long-term metastable state with increased electric conductance may be observed in the case of the asymmetric QW couple with the impurity delta shaped-layer in the narrower QW. It is not observed in the structures with other configurations. The observed effect is explained by the model accounting for metastable changes in the electron energy states spectrum in the studied structures caused by the strong electric field pulses.

Generation of super strong longitudinal electric field via vector superposition of linearly polarized laser beams

Radially polarized laser beams, which could generate longitudinal electric fields (LEF) in the far field after being focused have drawn increasing interest in wide fields. However, it is difficult to boost a radially polarized laser pulse to high peak power due to its spatially inhomogeneous polarization distribution. Here, we propose a vector superposition approach, firstly partition a linearly polarized beam into two parts in the near field, secondly modulate their polarization direction separately using the electro-optical effect and finally focus them using a high numerical aperture lens, thereby generating the LEF in the far field owing to vector superposition. This approach can amplify a laser pulse to the required peak power by using traditional schemes of the linearly polarized seed-pulse generation and multi-pass amplification, thereby efficiently scaling the LEF to the required magnitude. The simulation results support the theory in concluding that the approach would be a competent way to achieve super strong LEF in the far field of a laser beam.

Interaction of Ultraintense Radially-Polarized Laser Pulses with Plasma Mirrors

We present experimental results of vacuum laser acceleration (VLA) of electrons using radially polarized laser pulses interacting with a plasma mirror. Tightly focused radially polarized laser pulses have been proposed for electron acceleration because of their strong longitudinal electric field, making them ideal for VLA. However, experimental results have been limited until now because injecting electrons into the laser field has remained a considerable challenge. Here, we demonstrate experimentally that using a plasma mirror as an injector solves this problem and permits to inject electrons at the ideal phase of the laser, resulting in the acceleration of electrons along the laser propagation direction while reducing the electron beam divergence compared to the linear polarization case. We obtain electron bunches with few-MeV energies and a 200 pC charge, thus demonstrating for the first time electron acceleration to relativistic energies using a radially polarized laser. High-harmonic generation from the plasma surface is also measured and provides additional insight into the injection of electrons into the laser field upon its reflection on the plasma mirror. Detailed comparisons between experimental results and full 3D simulations unravel the complex physics of electron injection and acceleration in this new regime: we find that electrons are injected into the radially polarized pulse in the form of two spatially-separated bunches emitted from the p-polarized regions of the focus. Finally, we leverage on the insight brought by this study to propose and validate a more optimal experimental configuration that can lead to extremely peaked electron angular distributions and higher energy beams.

Laser microprocessing of metal surfaces using a tightly focused radially polarized beam.

Tight focusing of a radially polarized beam is used for single-shot laser ablation of metals. The strong longitudinal field is generated at the focus, and its contribution to the ablation process is comprehensively examined for various metal materials. In the presence of the longitudinal field at the focus, a fabricated crater at the surface exhibits either a spot shape or a doughnut shape, depending on the material. The experimental results indicate that the strong longitudinal electric field on metal surfaces is capable of promoting material removal, which may provide a novel processing scheme in ultrafast laser microprocessing with enhanced spatial resolution.

Influence of longitudinal mode components on second harmonic generation in III-V-on-insulator nanowires.

The large index contrast and the subwalength tranverse dimensions of nanowires induce strong longitudinal electric field components. We show that these components play an important role for second harmonic generation in III-V wire waveguides. To illustrate this behavior, an efficiency map of nonlinear conversion is determined based on full-vectorial calculations. It reveals that many different waveguide dimensions and directions are suitable for efficient conversion of a fundamental quasi-TE pump mode around the 1550 nm telecommunication wavelength to a higher-order second harmonic mode.

Generation of subdiffraction longitudinal bifoci by shaping a radially polarized wave

Lenses with two or more foci along the longitudinal direction exhibit immense potential in several optical applications. In this study, we propose an approach for generating subdiffraction longitudinal bifoci by binary-phase bifocal super-oscillatory lenses (SOLs), which are realized by simple AND operation between two single-foci SOLs with different focal lengths. Three bifocal SOLs with radiusRlens=70λ are designed at an operating wavelength of λ=118.8µm. Simulation results demonstrate that the minimum full width at half maximum (FWHM) is 0.397λ, and the maximum FWHM is 0.449λ, which is still smaller than the Abbe diffraction limit of 0.510λ, while all the sidelobe ratios are small (<15.1%). By properly choosing the focal length of the single-foci SOLs in the design process, the distance between the two foci can be easily controlled. Significantly, the generated bifoci with relatively uniform intensity contain a strong longitudinal electric field, which indicates their excellent prospects in optical imaging, particle acceleration, and other optical applications. In addition, the proposed bifoci-SOLs are based on the binary phase modulation, which facilitates easy fabrication compared with other approaches. These outstanding properties indicate the wide application prospects of bifocal SOLs.

Electromagnetic Burst Generation during Annihilation of Magnetic Field in Relativistic Laser-Plasma Interaction

We present the results of theoretical studies of formation and evolution of the current sheet in a colliosionless plasma during magnetic reconnection in relativistic limit. Relativistic magnetic reconnection is driven by parallel laser pulses interacting with underdense plasma target. Annihilation of laser created magnetic field of opposite polarity generates strong non-stationary electric field formed in between the region with opposite polarity magnetic field accelerating charged particles within the current sheet. This laser-plasma target configuration is discussed in regard with the laboratory modeling of charged particle acceleration and gamma flash generation in astrophysics. We present the results of 3-dimensional kinetic simulations and theoretical studies on the formation and evolution of the current sheet in a collisionless plasma during magnetic field annihilation in the ultra-relativistic limit. Annihilation of oppositively directed magnetic fields driven by two laser pulses interacting with underdense plasma target is accompanied by an electromagnetic burst generation. The induced strong non-stationary longitudinal electric field accelerates charged particles within the current sheet. Properties of the laser-plasma target configuration are discussed in the context of the laboratory modeling for charged particle acceleration and gamma flash generation in astrophysics.

A single-cell-gap transflective liquid crystal display with a vertically aligned cell

ABSTRACTA single-cell-gap transflective liquid crystal display with a vertically aligned cell using square ring electrode is demonstrated. The top substrate has a top planar common electrode, a square ring pixel electrode is coated on the bottom substrate, while a bumpy reflector is coated under the bottom substrate. In this device, the planar common electrode and square ring pixel electrode generate a strong longitudinal electric field in the transmissive region (T region) and a weak fringe field in the reflective region (R region). As result, the T and R regions accumulate the same optical phase retardation. The simulation results show that the display exhibits reasonably low operating voltage, high transmittance and well-matched voltage-dependent transmittance and reflectance curves. Besides, fabrication process of the transflective liquid crystal display is very simple.

Electron Acceleration by a Radially Polarized Laser Pulse in an Azimuthal Magnetic Field

Laser acceleration by radially polarized laser beams takes advantage of the strong longitudinal electric field component at the beam centre. When the laser field intensity is sufficiently high, it can push electrons initially at rest at the beam waist outside the Rayleigh zone and accelerate them to relativistic velocities along the laser axis. To obtain the best results in terms of electron dynamics and energy estimation, we suggest that the electrons could be accelerated to a very high energy level by the radially polarized laser pulse. The additionally used azimuthal magnetic field helps to retain the electron energy during acceleration. In this paper, we describe the electron energy scales with laser power and we explain how the laser beam parameter and the magnetic field both can be optimized for maximal acceleration.

Rayleigh–Taylor Instability and Excitation of Super-Dreicer Electric Fields in the Solar Chromosphere

Within the framework of the long-standing so-called “number problem” in the physics of solar flares, we consider the excitation of a super-Dreicer electric field at the leading edge of the electric current pulse that occurs at the chromospheric legs of a coronal magnetic loop as a result of the magnetic Rayleigh–Taylor instability. It is shown that for a sufficiently strong electric current, \(I_{0} \ge 10^{10}~\mbox{A}\), the current pulse propagates in the non-linear mode and generates a strong longitudinal electric field \(E_{z}\), which strongly depends on the current (\(E_{z} \propto I_{0}^{3}\)) and can exceed the Dreicer field (\(E_{z} > E_{\mathrm{D}}\)). In this case, the bulk of electrons in the site of the current pulse is in a runaway mode, and the energy release rate in the chromosphere increases significantly. Super-Dreicer electric fields also provide injection of protons into the regime of acceleration by Langmuir turbulence generated by fast electrons at the leading edge of the electric current pulse. The electric field at the pulse edge can exceed the Dreicer field starting from the chromosphere level with the number density \(n \approx 10^{13}~\mbox{cm}^{-3}\). At a lower current \(I_{0} < 10^{10}~\mbox{A}\), a super-Dreicer mode at the higher levels of the chromosphere with \(n < 10^{12}~\mbox{cm}^{-3}\) occurs.

Thermoelectric ionization of, D(-)-centers in a semiconductor quantum wire with a parabolic confinement potential in a strong longitudinal electric field

Conductivity of a semiconductor quantum wire with a parabolic confinement potential was studied within the framework of the zero-range potential model, containing donor impurities, in the longitudinal with respect to its axis electric field at low temperatures. A dispersion equation determining the dependence of the binding energy of the impurity on the electric field strength was obtained. It has been shown that the bound state of an electron on an impurity is destroyed by a strong electric field, i.e. the thermoelectric phenomenon of ionization occurs. It was found that under conditions of low temperatures the dependence of the current density in a quantum wire in the longitudinal electric field has a superlinear character.

Plasmonic lens focused longitudinal field excitation for tip-enhanced Raman spectroscopy.

A novel tip-enhanced Raman spectroscopy setup with longitudinal field excitation generated by a plasmonic lens is investigated. A symmetry-breaking structure plasmonic lens that is expected to realize a strong longitudinal electric field focus has been designed to generate suitable excitation for enhancement in a tip antenna. The focusing performance of the plasmonic lens is theoretically simulated by the finite-difference time-domain method and experimentally verified by the detection of optical near-field distribution. A plasmonic lens assisted tip-enhanced Raman spectroscopy setup has been constructed and used to investigate specimens of carbon nanotubes. Tip-enhanced Raman spectra with distinct excitation wavelengths show similar Raman shifts but different intensities. Experimental results presented in this paper demonstrate that the Raman signal is considerably enhanced. It indicates that the novel tip-enhanced Raman spectroscopy configuration is feasible and is a promising technique for tip-enhanced Raman spectroscopy measurements and characterizations.

Open charm production in p + p and Pb + Pb collisions at the CERN Large Hadron Collider

Effects of strong longitudinal color electric fields, shadowing, and quenching on the production of prompt open charm mesons (D0, D+, D, D) in central Pb + Pb collisions at = 2.76 TeV are investigated within the framework of the HIJING/B v2.0 model. We compute the nuclear modification factor RPbPbD, and show that the above nuclear effects constitute important dynamical mechanisms in the description of experimental data. The strength of color fields (as characterized by the string tension κ), partonic energy loss and jet quenching process lead to a suppression factor consistent with recent published data. Predictions for beauty mesons are presented. In addition, ratios of strange to non-strange prompt charm mesons in central Pb + Pb and minimum bias (MB) collisions at 2.76 TeV are also discussed. MB collisions which constitute a theoretical baseline in our calculations are studied at centre of mass energies = 2.76 TeV and 7 TeV.

A new type of localized fast moving electronic excitations in molecular chains

It is shown that in a Holstein molecular chain placed in a strong longitudinal electric field some new types of excitations can arise. These excitations can transfer a charge over large distance (more than 1000 nucleotide pairs) along the chain retaining approximately their shapes. Excitations are formed only when a strong electric field either exists or quickly arises under especially preassigned conditions. These excitations transfer a charge even in the case when Holstein polarons are practically immobile. The results obtained are applied to synthetic homogeneous PolyG/PolyC DNA duplexes. They can also be provide the basis for explanation of famous H.W. Fink and C. Schönenberger experiment on long-range charge transfer in DNA.

Tip-enhanced Raman spectroscopy mapping with strong longitudinal field excitation

Longitudinal electric field illumination is greatly effective for enhancing the local electric field and Raman signal at the tip apex in tip-enhanced Raman spectroscopy (TERS). In this work, the optical field distribution of tightly focused radially polarized (RP) beam on the focal plane is calculated according to vector diffraction theory and the effectiveness of longitudinal field excitation on Raman signal enhancement is experimentally verified. An RP beam generated by a liquid crystal spatial light modulator is focused via a high numerical-aperture objective lens to form a strong longitudinal electric field at the focus. The focused field is utilized to excite single-walled nanotubes sample in TERS experiments. The experimental results demonstrate that the enhancement factor of RP excitation is obviously higher compared with linearly polarized illumination. And then, the corresponding TERS mapping and topography are simultaneously characterized.