Longitudinal Plasma Waves Research Articles

Optical Absorption in Tilted Geometries as an Indirect Measurement of Longitudinal Plasma Waves in Layered Cuprates.

Electromagnetic waves propagating in a layered superconductor with arbitrary momentum, with respect to the main crystallographic directions, exhibit an unavoidable mixing between longitudinal and transverse degrees of freedom. Here we show that this basic physical mechanism explains the emergence of a well-defined absorption peak in the in-plane optical conductivity when light propagates at small tilting angles relative to the stacking direction in layered cuprates. More specifically, we show that this peak, often interpreted as a spurious leakage of the c-axis Josephson plasmon, is instead a signature of the true longitudinal plasma mode occurring at larger momenta. By combining a classical approach based on Maxwell's equations with a full quantum derivation of the plasma modes based on modeling the superconducting phase degrees of freedom, we provide an analytical expression for the absorption peak as a function of the tilting angle and light polarization. We suggest that an all-optical measurement in tilted geometry can be used as an alternative way to access plasma-wave dispersion, usually measured by means of large-momenta scattering techniques like resonant inelastic X-ray scattering (RIXS) or electron energy loss spectroscopy (EELS).

Спектральные характеристики плазменных волн ионосферы при возбуждении мощными КВ-радиоволнами на частотах излучения вблизи гирогармоник электронов и критической частоты слоя F2

We present the result of the studies into characteristics of high-latitude ionospheric F-region longitudinal plasma waves (Langmuir and ion-acoustic), caused by the impact of powerful HF radio waves of ordinary (O-mode) or extraordinary (X-mode) polarization of the EISCAT/Heating facility, Tromsø, Norway. The powerful HF radio waves on October 20, 2012 and February 26, 2013 were emitted in the direction of the magnetic zenith with a step change in the effective radiation power (ERP). The radiation frequency fH of the EISCAT/Heating facility on February 26, 2013 was close to the F2-layer critical frequency foF2 (fH/foF2~1) and exceeded the electron gyroresonance frequency fH>5fce. On October 20, 2012, the conditions fH/foF2~0.85–0.95 and fH<6fce were fulfilled. Analysis of EISCAT measurements of an incoherent scatter radar (ISR) at a frequency of 930 MHz, spatially aligned with the heating facility for radiation conditions ERP<200 MW, has shown that parametric decay instabilities are excited at the ionospheric heights where the pump frequency is close to the plasma Langmuir frequency, fH≈fPL. We have studied peculiarities of excitation of the decay parametric instabilities as a function of height in the ionosphere and pump wave polarization, the ratios between fH and foF2, and also fH and nfce.

Spectral features of ionospheric plasma waves excited by powerful HF radio waves radiated at frequencies near electron gyroharmonics and F2-layer critical frequency

We present the result of the studies into characteristics of high-latitude ionospheric F-region longitudinal plasma waves (Langmuir and ion-acoustic), caused by the impact of powerful HF radio waves of ordinary (O-mode) or extraordinary (X-mode) polarization of the EISCAT/Heating facility, Tromsø, Norway. The powerful HF radio waves on October 20, 2012 and February 26, 2013 were emitted in the direction of the magnetic zenith with a step change in the effective radiation power (ERP). The radiation frequency fH of the EISCAT/Heating facility on February 26, 2013 was close to the F2-layer critical frequency foF2 (fH/foF2~1) and exceeded the electron gyroresonance frequency fH>5fce. On October 20, 2012, the conditions fH/foF2~0.85–0.95 and fH<6fce were fulfilled. Analysis of EISCAT measurements of an incoherent scatter radar (ISR) at a frequency of 930 MHz, spatially aligned with the heating facility for radiation conditions ERP<200 MW, has shown that parametric decay instabilities are excited at the ionospheric heights where the pump frequency is close to the plasma Langmuir frequency, fH≈fPL. We have studied peculiarities of excitation of the decay parametric instabilities as a function of height in the ionosphere and pump wave polarization, the ratios between fH and foF2, and also fH and nfce.

Femtosecond laser-induced sub-wavelength plasma inside dielectrics. II. Second-harmonic generation

Second-harmonic emission at a frequency that is twice the laser frequency is an important diagnostic for nonlinear laser–plasma interaction. It is forbidden for centrosymmetric materials such as the bulk of sapphire. The symmetry, however, can be broken by dielectric discontinuities as a result of plasma generation inside a solid dielectric. In the present work, we explore the basic characteristics of experimentally observed second-harmonic emission during focusing a femtosecond Bessel beam inside sapphire. We employ three-dimensional particle-in-cell simulations and the Helmholtz wave equation for theoretical investigations. We analyze how the efficiency of second-harmonic generation and its polarization depend on the plasma parameters. We find that the second-harmonic is generated either due to the coalescence of two-surface electromagnetic waves or nonlinear interaction between the transverse electromagnetic wave and the longitudinal electron plasma wave driven by linear mode conversion. Experimental results agree with the theoretical predictions and confirm the existence of over-critical plasma inside the sapphire that is essential for the resonance of plasma waves or excitation of surface plasmons.

Kinetic phenomena of helical plasma waves with orbital angular momentum

An accurate description of plasma waves is fundamental for the understanding of many plasma phenomena. It is possible to twist plasma waves such that, in addition to having longitudinal motion, they can possess a quantized orbital angular momentum. One such type of plasma wave is the Laguerre–Gaussian mode. Three-dimensional numerical particle-in-cell simulations demonstrate the existence of stable long-lived plasma waves with orbital angular momentum. These waves can be shown to create large amplitude static magnetic fields with unique twisted longitudinal structures. In this paper, we review the recent progress in studies of helical plasma waves and present a new analytical description of a standing Laguerre–Gaussian plasma wave mode along with 3D particle-in-cell simulation results. The Landau damping of twisted plasma waves shows important differences compared to standard longitudinal plasma wave Landau damping. These effects include an increased damping rate, which is affected by both the focal width and the orbital number of the plasma wave. This increase in the damping rate is of the same order as the thermal correction. Moreover, the direction of momentum picked up by resonant particles from the twisted plasma wave can be significantly altered. By contrast, the radial electric field has a subtle effect on the trajectories of resonant electrons.

Optimized window to produce ultra-intense and ultra-compressed laser pulses by Stimulated Brillouin Scattering

We propose a theoretical model to produce ultra-intense and ultra-compressed laser pulses based on Stimulated Brillouin Scattering (SBS) process. The amplification of laser pulses via Brillouin amplification process is obtained when three waves (two transverse electromagnetic waves and a longitudinal plasma wave) couple in the plasma when resonance condition for energy (frequency ω) and momentum (wave-vector k) is satisfied. Counter propagating seed pulse takes energy from laser pulse when they interact with each other via the process of stimulated Brillouin scattering and finally it gets amplified and compressed. We optimize the parameters (like initial plasma density, initial laser pulse intensity, interaction time, wave breaking time, fillamentation time etc.) for SBS compression and amplification to obtain high intensity laser pulse. This optimized window exactly match with the simulation results reported by Weber et al. [1]. Due to strong SBS within the optimum parametric window, one can develop compact plasma-based amplifier, which can produce high intensity short laser pulse. This technique offers damage less amplification of laser pulses. The amplification and compression ratio obtained in this model are 94 and 30, respectively. These intensities can be used as seed intensities to obtain Zetta watt laser pulses using C-3 (Cascade, Conversion and Compression) technique reported by Mourou et al. [2].

Electron Dynamics in the Field of Strong Plasma and Electromagnetic Waves: A Review

Collective methods of charged particle acceleration provide an approach towards achieving high-energy particle beams with relatively compact accelerator facilities. Among the collective acceleration methods, one of the central places belong to the electron Laser Wakefield Acceleration concept, when the regular accelerating structure in the form of longitudinal electrostatic wave propagating with the phase speed close to speed of light in vacuum is generated by ultrashort laser pulse in collisionless plasma. The review article contains theoretical description of charged particle (electron) interaction with various configurations of the electromagnetic field and with the longitudinal plasma waves. The radiation dominated regimes of the electron interaction with strong electromagnetic waves, when the radiation friction force effects play the key role, are also discussed.

A rotation-driven pulsar radio emission mechanism

ABSTRACT We propose and discuss an alternative pulsar radio emission mechanism that relies on rotation-driven plasma oscillations, rather than on a beam-driven instability, and suggest that it may be the generic radio emission mechanism for pulsars. We identify these oscillations as superluminal longitudinal waves in the pulsar plasma and point out that these waves can escape directly in the O mode. We argue that the frequency of the oscillations is ω0 ≈ ωp(2〈γ〉)1/2/γs, where γs is the Lorentz factor of bulk streaming motion and 〈γ〉 is the mean Lorentz factor in the rest frame of the plasma. The dependence of the plasma frequency ωp on radial distance implies a specific frequency-to-radius mapping, ω0∝r−3/2. Escape of the energy in these oscillations is possible if they are generated in overdense, field-aligned regions that we call fibres; the wave energy is initially refracted into underdense regions between the fibres, which act as ducts. Some implications of the model for the interpretation of pulsar radio emission are discussed.

Double and triple resonance behaviour in large systems of LC-shunted intrinsic Josephson junctions

We study the current-voltage characteristics and phase dynamics of intrinsic Josephson junctions shunted by inductive and capacitive circuit elements. Here we investigate double and triple resonances that leads to charging of the superconducting layers in shunted stacks of junctions. We study numerically the dynamical response of the system to sweeping dc-bias currents, such as would typically be used in experiments. Our simulations reveal a series of features in the current-voltage characteristic of the system. In particular, we show that for larger numbers of junctions (N⪆15) the shunting causes charging to occur even along the outermost branch of the current-voltage characteristic. This charging on the outermost branch is associated with travelling wave solutions that become more stable than fully synchronous solutions in the shunted stacks with larger numbers of junctions. We observe a transformation of the travelling wave solution into a standing wave solution associated with a longitudinal plasma wave.

The new structure of analytical and semi-analytical solutions of the longitudinal plasma wave equation in a magneto-electro-elastic circular rod

This research paper extracts novel analytical and semi-analytical wave solutions of the longitudinal wave equation in a magneto-electro-elastic circular rod by using the modified Khater method as one of the most novel and general computational methods and the Adomian decomposition method as a semi-analytical method. The longitudinal waves in metallic thin films are explained for the first time by Nilsson and Lindau, who used the visual evidence. They noted subdued anomalies in the ports of thin ([Formula: see text]100 Å) Ag layers deposited on amorphous silica for p-polarized light at frequencies padlock to the dynamic plasma frequency. These properties are studied by our two suggested methods and are explained by sketching some of our obtained solutions. Moreover, the stability property is tested for our obtained solutions by using the features of the Hamiltonian system. The performance of our used methods shows the power and effectiveness of these methods and their ability to apply on many different forms of nonlinear partial differential equations.

Waves in plasma formed by above-threshold ionization of gas atoms

In the regime of above-threshold ionization of gas atom in the field of laser radiation, plasma with photoelectron distribution consisting of peaks at discrete energy values is formed. It is shown that the number of longitudinal waves in such plasma coincides with the number of peaks in the distribution function. When peaks practically don't overlap, the dispersion law of each wave in the region of short waves is determined by electrons from the corresponding peak. In this case the phase and group velocities of the waves are close to the electron velocity, which corresponds to the peak maximum. It is possible to talk about such waves as an electronic sound, since the perturbations of the electron density mainly arise due to pressure perturbations. When the peaks are narrow, but having a finite width, the Cherenkov damping of waves is exponentially small. Numerical calculations the dispersion laws for of the two and four waves in photoionized xenon plasma, in which the electron distribution function consists of two or four narrow peaks are given.

Features of the Dynamics of a System of Coupled Josephson Junctions with Topologically Trivial and Nontrivial Barriers: Manifestation of the Majorana Mode

The appearance of parametric resonance and the excitation of a longitudinal plasma wave in a system of coupled Josephson junctions with topologically trivial and nontrivial barriers have been demonstrated. The voltage at resonance as a function of the dissipation parameter has a minimum at which the parametric resonance condition changes from ωJ = 2ωLPWtoωJ = ωLPW, where is the Josephson frequency and ωLPW is the frequency of the formed longitudinal plasma wave. The position of this minimum for the system with nontrivial barriers is shifted from that for the system with trivial barriers. This shift can be used to identify the appearance of Majorana states.

High-power terahertz emission from a plasma penetrated by counterstreaming different-size electron beams

It is found that multi-cycle pulses of high-power coherent terahertz radiation can be efficiently generated in a plasma by counterstreaming long-pulse electron beams driving potential plasma waves via the two-stream instability. Instead of the well-known three-wave interaction processes between oblique beam-driven modes, we propose to generate electromagnetic radiation near the doubled plasma frequency due to the novel and much more efficient mechanism based on the head-on collision of longitudinal plasma waves with mismatching potential profiles. It is shown that this radiation mechanism can be implemented experimentally either by the collision of low-density electron beams with different transverse sizes or by the counter injection of denser equal-size beams unstable against filamentation perturbations. Particle-in-cell simulations for kiloampere electron beams capable of focusing into millimeter-scale sizes demonstrate the possibility to reach the high efficiency of beams-to-THz power conversion (3%–7%), which opens the path to gigawatt-class THz sources with a narrow spectral line.

Unexpected impact of radiation friction: enhancing production of longitudinal plasma waves

We study the penetration of ultra-intense (intensity Isimeq 1023–24 W/cm2) circularly polarized laser pulses into a thick subcritical plasma layer with accounting for radiation friction. We show that radiation pressure is enhanced due to radiation friction in the direction transverse to the laser pulse propagation, and that for stronger and longer laser pulses this mechanism dominates over the ordinary ponderomotive pressure, thus resulting in a substantionaly stronger charge separation than anticipated previously. We give estimates of the effect and compare them with the results of one and two dimensional particle-in-cell simulations. This effect can be important for laser-based acceleration schemes.

Longitudinal electron waves in plasma formed at multi‐photon ionization of atoms by a short laser pulse

The dispersion law and the collisionless damping decrement of high‐frequency waves in a plasma formed as a result of multi‐photon ionization of atoms by a laser pulse are found. Estimates indicating that such waves may exist in a weakly ionized xenon plasma are given.

Resonant plasma excitation by single-cycle THz pulses

In this paper, an alternative perspective for the generation of millimetric high-gradient resonant plasma waves is discussed. This method is based on the plasma-wave excitation by energetic single-cycle THz pulses whose temporal length is comparable to the plasma wavelength. The excitation regime discussed in this paper is the quasi-nonlinear regime that can be achieved when the normalized vector potential of the driving THz pulse is on the order of unity. To investigate this regime and determine the strength of the excited electric fields, a Particle-In-Cell (PIC) code has been used. It has been found that by exploiting THz pulses with characteristics currently available in laboratory, longitudinal electron plasma waves with electric gradients up to hundreds MV/m can be obtained. The mm-size nature of the resonant plasma wave can be of great utility for an acceleration scheme in which high-brightness electron bunches are injected into the wave to undergo a strong acceleration. The long-size nature of the acceleration bucket with respect to the short length of the electron bunches can be handled in a more robust manner in comparison with the case when micrometric waves are employed.

Conversion of Transverse to Longitudinal Plasma Waves Induced by Radiation Reaction

We investigate the evolution of a circularly polarized wave in a cold plasma in a regime when radiation reaction is essential. A new effect is that circularly polarized transverse waves become unstable with respect to partial conversion to the longitudinal ones. This effect appears due to radiation reaction entirely and in principle could be implemented for particle acceleration. We provide analytical expression for arising longitudinal field in the case, when it is much smaller, than transverse one.

Modeling of LC-shunted intrinsic Josephson junctions in high-Tc superconductors

Resonance phenomena in a model of intrinsic Josephson junctions shunted by LC-elements (L-inductance, C-capacitance) are studied. The phase dynamics and IV-characteristics are investigated in detail when the Josephson frequency approaches the frequency of the resonance circuit. A realization of parametric resonance through the excitation of a longitudinal plasma wave, within the bias current interval corresponding to the resonance circuit branch, is demonstrated. It is found that the temporal dependence of the total voltage of the stack, and the voltage measured across the shunt capacitor, reflect the charging of superconducting layers, a phenomenon which might be useful as a means of detecting such charging experimentally. Thus, based on the voltage dynamics, a novel method for the determination of charging in the superconducting layers of coupled Josephson junctions is proposed. A demonstration and discussion of the influence of external electromagnetic radiation on the IV-characteristics and charge-time dependence is given. Over certain parameter ranges the radiation causes an interesting new type of temporal splitting in the charge-time oscillations within the superconducting layers.

Terahertz radiation driven by two-color laser pulses at near-relativistic intensities: Competition between photoionization and wakefield effects.

We numerically investigate terahertz (THz) pulse generation by linearly-polarized, two-color femtosecond laser pulses in highly-ionized argon. Major processes consist of tunneling photoionization and ponderomotive forces associated with transverse and longitudinal field excitations. By means of two-dimensional particle-in-cell (PIC) simulations, we reveal the importance of photocurrent mechanisms besides transverse and longitudinal plasma waves for laser intensities >1015 W/cm2. We demonstrate the following. (i) With two-color pulses, photoionization prevails in the generation of GV/m THz fields up to 1017 W/cm2 laser intensities and suddenly loses efficiency near the relativistic threshold, as the outermost electron shell of ionized Ar atoms has been fully depleted. (ii) PIC results can be explained by a one-dimensional Maxwell-fluid model and its semi-analytical solutions, offering the first unified description of the main THz sources created in plasmas. (iii) The THz power emitted outside the plasma channel mostly originates from the transverse currents.

Cascade of parametric resonances in coupled Josephson junctions

We found that the coupled system of Josephson junctions under external electromagnetic radiation demonstrates a cascade of parametric instabilities. These instabilities appear along the IV characteristics within bias current intervals corresponding to Shapiro step subharmonics and lead to charging in the superconducting layers. The amplitudes of the charge oscillations increase with increasing external radiation power. We demonstrate the existence of longitudinal plasma waves at the corresponding bias current values. An essential advantage of the parametric instabilities in the case of subharmonics is the lower amplitude of radiation that is needed for the creation of the longitudinal plasma wave. This fact gives a unique possibility to create and control longitudinal plasma waves in layered superconductors. We propose a novel experiment for studying parametric instabilities and the charging of superconducting layers based on the simultaneous variation of the bias current and radiation amplitude.