Excitation Of Surface Plasma Waves Research Articles

Surface plasma wave excitation using laser beat-wave and terahertz generation

In this paper, a study of surface plasma wave excitation from a magnetized metallic surface using two co-propagating lasers is conducted. Two lasers propagating in the same direction with frequency difference of plasmon frequency of the metal excite plasma oscillations on the metallic surface, which generate surface plasma waves. The transverse components of the field associated with these surface plasma wave lead to excite transverse current at terahertz frequency. We report a systematic theoretical model for this study and subsequent numerical results are presented for THz field estimation.

Key parameters for surface plasma wave excitation in the ultra-high intensity regime

Ultra-short high-power lasers can deliver extreme light intensities (≥1020 W/cm2 and ≤30 fs) and drive large amplitude Surface Plasma Wave (SPW) at over-dense plasma surface. The resulting current of energetic electron has great interest for applications, potentially scaling with the laser amplitude, provided that the laser–plasma transfer to the accelerated particles mediated by SPW is still efficient at ultra-high intensity. By means of particle-in-cell simulations, we identify the best condition for SPW excitation and show a strong correlation between the optimum surface plasma wave excitation angle and the laser's angle of incidence that optimize the electron acceleration along the plasma surface. We also discuss how plasma density and plasma surface shape can be adjusted in order to push to higher laser intensity the limit of surface plasma wave excitation. Our results open the way to new experiments on forthcoming multi-petawatt laser systems.

Plasmonic-coupled quantum dot photodetectors for mid-infrared photonics.

A plasmonic-coupled, InAs-based quantum dot photodetector fabricated for mid-wave infrared photonics is reported. The detector is designed to provide a broadband absorption [full width at half maximum (FWHM) ≳ 2 µm] peaked at ∼5.5 µm, corresponding to transitions from the ground state of the quantum dot to the quasi-continuum resonance state above the quantum well. From the coupling of this transition to the surface plasma wave (SPW) excited by an Au film atop the detector, fabricated with a 1.5 µm-period, 2-dimensional array of square holes, a narrowband SPW enhancement peaked at 4.8 µm with an FWHM less than 0.5 µm is achieved. At ∼90 K, a peak responsivity enhanced ∼5× by the plasmonic coupling is observed. Simulation reveals that this enhancement corresponds to collecting ∼6% of the incident light; ∼40% of the total absorption by the SPW excitation at the peak wavelength.

Excitation of surface plasma waves by an electron beam in a magnetized dusty plasma – Reinvestigated

Surface plasma waves have been an important subject of theoretical and experimental studies. Prakash and Sharma [1] have investigated excitation of surface plasma waves by an electron beam in a magnetized dusty plasma. While understanding that work, we have found several major discrepancies there. In our approach, we have considered basic equations and have gone through mathematical details systematically. Two expressions for ω are found, and both of them have real values, showing that there is no growth rate. It contradicts the results of Prakash and Sharma [1]. We have not found any role of dust particle in the plasma fluid.

Excitation of surface plasma waves and fast electron generation in relativistic laser\u2013plasma interaction

The excitation of surface plasma waves (SPW) by an intense short laser pulse is a useful tool to enhance the laser absorption and the electron heating in the target. In this work, the influence of the transverse laser profile and the pulse duration used to excited SPW is investigated from Fluid and 2D Particle-in-Cell simulations. We show the existence of a lobe of surface plasma wave modes. Our results highlight surface plasma waves excitation mechanism and define the laser parameters to optimise the SPW excitation and the kinetic energy of the associated electron trapped in the wave. It opens the door to monitor the spectral mode distribution and temporal shape of the excited surface waves in the high relativistic regime. The most important result of the study is that—at least in 2D—the charge and the energy of the electron bunches depend essentially on the laser energy rather than on temporal or spatial shape of the laser pulse.

A theory of electrodynamic response for bounded metals: Surface capacitive effects

We report a general macroscopic theory for the electrodynamic response of semi-infinite metals (SIMs). The theory includes the hitherto overlooked capacitive effects due to the finite spatial extension of a surface. The basic structure of this theory is independent of the particulars of electron dynamics. Analytical expressions have been obtained of the charge density–density response function, which is naturally parsed into two parts. One of them represents a bulk property while the other a pure surface property. We apply the theory to study the responses according to several electronic dynamics models and provide a unified view of their validity and limitations. The models studied include the local dielectric model (DM), the dispersive hydrodynamic model (HDM) and specular reflection model (SRM), as well as the less common semi-classical model (SCM) based on Boltzmann’s transport equation. We show that, in terms of their basic equations, the SRM is an extension of the HDM, just as the HDM is an extension of the DM. The SCM improves over the SRM critically through the inclusion of translation symmetry breaking and surface roughness effects. We then employ the response function to evaluate the so-called dynamical structure factor, which plays an important role in particle scattering. As expected, this factor reveals a peak due to the excitation of surface plasma waves (SPWs). Surprisingly, however, the peak is shown to be considerably sharper in the SCM than in other models, indicating an incipient instability of the system according to this model. We also study the distribution of charges induced by a charged particle grazing over a SIM surface at constant speed. This distribution is shown to contain model-specific features that are of immediate experimental interest. This work is expected to find broad applications in optics, plasmonics and other areas such as electron energy loss spectroscopy and accelerator design.

Excitation of Surface Waves during by an Inhomogeneous Electromagnetic Wave Incident on the Plasma Boundary

We have studied the excitation of surface plasma waves during the propagation of a cylindrical electromagnetic wave in a layered plasma–dielectric medium. The dielectric—vacuum—plasma and vacuum–plasma–plasma layers have been considered. It is shown that no surface waves are excited by the cylindrical electromagnetic wave at the plasma–dielectric boundary (like in the case of a plane wave). A surface wave in a layered medium is excited in a quite narrow range of frequencies and angles of propagation. We have calculated the structures of the electromagnetic field and the electromagnetic energy flux and determined the integral reflection and transmission coefficients using both numerical an analytic asymptotic methods. It is shown that the contribution of the field from the lateral wave is negligibly small in all cases.

Excitation of Surface Plasma Waves in Microwave Radiation Sources by Electron Beam with Allowance for Thermal Velocity Spread

Based on the hydrodynamic model, in the linear approximation, the problem of excitation by an electron beam of surface waves in electrodynamic systems of plasma relativistic microwave electronics has been considered with consideration of electron velocity spread. Complex instability increments have been determined for complex parameters of the beam-plasma system. Two instability regimes differing in the dynamics of beam plasma oscillations during instability development have been observed: Compton (singleparticle) and Raman (collective) instabilities. The role of thermal effects in an electron beam and its density in the formation of a particular mode of beam instability has been analyzed.

Parametric excitation of surface plasma waves over a metallic surface by laser in an external magnetic field

AbstractEffects of external static magnetic field (applied in$\hat y$-direction) on resonant excitation of surface plasma waves (SPW) have been investigated over the metal free space interface. The high power laser$({\rm \omega} _0,\;\vec k_{0z})$is incident over the metal surface and exerts a ponderomotive force on the metal electrons in the skin layer. The ponderomotive force disturbs the quasi-neutrality of plasma which results into the excitation of space charge field at the frequency 2ω0. The electron density perturbation at frequency 2ω0driven by self-consistent space charge potential couples with the oscillatory velocity due to the seed SPW$({\rm \omega}, \;\vec k_z)$and produces nonlinear current to drive another counter propagating SPW$({\rm \omega} _1,\;\vec k_{1z})$at the phase matching conditions of frequency ω = ω1− 2ω0and wavenumber$\vec k_z = \vec k_{1z} - 2\vec k{}_{0z}$(by feedback mechanism). The parametric process becomes resonant at 2ω0≈ ωpand the maximum growth rate is achieved for an incidence angle of laser θ = 40°. The growth rate of the process reduces to half on increasing the magnetic field from 0.49 to 2.45 MG. The present study may be significant to the laser absorption experiments where surface rippling can strongly affect the laser energy absorption.

Parametric excitation of surface plasma waves by stimulated Compton scattering of laser beam at metal-free space interface

AbstractAn obliquely incident high-power laser (ω0,k0z) on the metallic surface can resonantly excite a surface plasma wave (SPW) (ω1,k1z) and a quasi-electrostatic plasma wave (ω,kz) inside the skin layer at the phase-matching conditions of frequency ω1= ω − ω0and wave numberk1z=kz−k0z. The oscillating electrons in the skin layer couples with the seed SPW and exert non-linear ponderomotive force on electrons at the frequency of quasi-static mode. Density perturbations due to quasi-static mode and ponderomotive force associate with the motion of electrons (due to incident laser) and give rise to a non-linear current by feedback mechanism. At ω/kz~vF(wherevFis the Fermi velocity of metal) this non-linear current is responsible for the growth of SPW. The maximum growth of the present process (≅1.5 × 1012s−1) is achieved at incident angle θ = 42° for laser frequency ω0= 2 × 1015rad/s. Growth of SPW enhances from 1.62 × 1011to ≅1.5 × 1012s−1as the magnetic field changes from 12 to 24 MG. The excited SPW can be utilized for surface heating and diagnostics purpose.

Optical excitation of surface plasma waves without grating structures

Surface plasma waves (SPWs) are usually discussed in the context of a metal in contact with a dielectric. However, they can also exist between two metals. In this work we study these bimetallic waves. We find that their dispersion curve always cuts the light line, which allows direct optical coupling without surface grating structures. We propose practical schemes to excite them and the excitation efficiency is estimated. We also show that these waves can be much less lossy than conventional SPWs and their losses can be systematically controlled, a highly desirable attribute in applications. Conducting metal oxides seem fit for experimental studies.

Surface plasma waves with their harmonics generation from pre-structured targets

Surface plasma waves with their harmonics are generated from pre-structured targets. The harmonics are generated by coherent synchrotron emission or relativistically oscillating mirror and then resonantly amplified by surface plasma wave excitation. Two dimensional particle-in-cell simulations and the theoretical analysis show that the laser is coupled to the structured target by generating a periodic current. Some of the generated harmonics have half integer wave numbers but integer frequencies. This interesting phenomenon is controlled by the structure period of the target.

Laser excitation of terahertz surface plasma wave over a hollow capillary plasma

AbstractTwo collinear laser pulses of finite spot size propagating through a capillary plasma, modeled as a hollow plasma cylinder, are shown to produce beat frequency terahertz (THz) surface plasmons at the inner surface. The evanescent laser fields in the plasma impart oscillatory velocity to electrons and exert a beat ponderomotive force on them. The static component of the ponderomotive force inhibits plasma from filling the vacuum region while the beat frequency component produces a nonlinear current (${\vec J^{{\;\rm NL}}}$) that drives the difference frequency THz surface plasma wave (SPW). Phase matching for the THz surface wave excitation is achieved when the group velocity of the lasers equals the phase velocity of the beat frequency SPW. At laser intensities of ~1014W/cm2at 10 μm wavelength, one may attain normalized surface wave amplitude ~ 0.03.

Study of strong enhancement of synchrotron radiation via surface plasma waves excitation by particle-in-cell simulations

Synchrotron radiation is strongly enhanced by the resonant excitation of surface plasma waves (SPWs). Two-dimensional particle-in-cell simulations show that energy conversion efficiency from laser to radiation in the case of SPWs excitation is about 18.7%, which is improved by more than 2 orders of magnitude compared with that of no SPWs excitation. Besides the high energy conversion efficiency, the frequency spectrum and the angular distribution of the radiation are also improved in the case of SPWs excitation because of the quasi-static magnet field induced by surface plasma waves excitation.

Terahertz surface plasmon excitation over a bismuth thin film by an electron beam

The excitation of terahertz surface plasma wave (SPW) over bismuth thin film-glass structure by a parallel propagating electron beam is studied. The SPW phase velocity is sensitive to the thickness of bismuth film and it is driven via the Cerenkov resonance. The growth rate for terahertz radiation generation by an electron beam is obtained under small signal approximation.

Surface wave excitation by a density modulated electron beam in a magnetized dusty plasma cylinder

AbstractThis paper studies the surface plasma wave excitation via Cerenkov and fast cyclotron interaction by a density modulated electron beam propagating through a magnetized dusty plasma cylinder. The dispersion relation of surface plasma waves has been derived and it has been shown that the phase velocity of waves increases with increase in relative density δ(=nio/ne0,whereni0is the ion plasma density andne0is the electron plasma density) of negatively charged dust grains. The beam radius is taken slightly less than the radius of dusty plasma cylinder. The frequency and the growth rate of the unstable wave instability increases with increase in the value of δ and normalized frequency ω/ωpe. The growth rate of the instability increases with the beam density and scales as one-third power of the beam density in Cerenkov interaction and square root of beam density in fast cyclotron interaction. The dispersion relation of surface plasma waves has been retrieved from the derived dispersion relation by considering that the beam is absent and there are no dust grains in the plasma cylinder.

Effect of relativistic elliptical beam modulation on excitation of surface plasma waves in a magnetized dusty plasma column with elliptical cross section

The excitation of surface plasma waves due to the interaction of an elliptical relativistic density modulated electron beam with the magnetized dusty plasma column with elliptical cross-section has been studied. The dispersion relation of surface plasma waves has been retrieved from the derived dispersion relation by considering that the beam is absent and there is no dust in the plasma elliptical cylinder. It is shown that the Cherenkov and fast cyclotron interactions appear between the beam and eigen-modes of plasma column. The growth rate of the instability increases with the beam density and modulation index as one-third power of the beam density in Cherenkov interaction and is proportional to the square root of beam density in fast cyclotron interaction. The numerical results and graphs are presented, too.

Improved ion acceleration via laser surface plasma waves excitation

The possibility of enhancing the emission of the ions accelerated in the interaction of a high intensity ultra-short (<100 fs) laser pulse with a thin target (<10λ0), via surface plasma wave excitation is investigated. Two-dimensional particle-in-cell simulations are performed for laser intensities ranging from 1019 to 1020 Wcm−2μm2. The surface wave is resonantly excited by the laser via the coupling with a modulation at the target surface. In the cases where the surface wave is excited, we find an enhancement of the maximum ion energy of a factor ∼2 compared to the cases where the target surface is flat.

About excitation of surface plasma waves by elliptical relativistic electron beam in a magnetized dusty plasma column with elliptical cross section

The surface plasma waves in a magnetized dusty plasma elliptical cylinder driven by elliptic relativistic electron beam propagating inside the elliptical cylinder are studied. The dispersion relation of surface plasma waves has been retrieved from the derived dispersion relation by considering that the beam is absent and there is no dust in the plasma cylinder. Mathematically, it is shown that the beam can interact with the surface plasma waves via Cerenkov interaction and fast cyclotron interaction. The growth rate and phase velocity in every cases are obtained. Finally, the numerical results and graphs are presented.

Surface plasma wave excitation via laser irradiated overdense plasma foil

A laser irradiated overdense plasma foil is seen to be susceptible to parametric excitation of surface plasma wave (SPW) and ion acoustic wave (IAW) on the ion plasma period time scale. The SPW is localised near the front surface of the foil while IAW extends upto the rear. The evanescent laser field and the SPW exert a ponderomotive force on electrons driving the IAW. The density perturbation associated with the latter beats with the laser induced oscillatory electron velocity to drive the SPW. At relativistic laser intensity, the growth rate is of the order of ion plasma frequency.