Laser Beam In Collisionless Plasma Research Articles

Three propagation regimes of Laguerre–Gaussian laser beams in collisionless plasma

Three propagation regimes of Laguerre–Gaussian laser beams in collisionless plasma

Self-focusing of Laguerre–Gaussian laser beams in collisionless plasma: paraxial-like approach

Self-focusing of Laguerre–Gaussian laser beams in collisionless plasma: paraxial-like approach

Self-focusing, self-trapping and self-phase modulation of elliptical q-Gaussian laser beams in collisionless plasma

Self-focusing, self-trapping and self-phase modulation of elliptical q-Gaussian laser beams in collisionless plasma

Self-Focusing and Defocusing of Lorentz-Gauss Laser Beam in Collisionless Plasma

Self-Focusing and Defocusing of Lorentz-Gauss Laser Beam in Collisionless Plasma

Second harmonic generation of zeroth-order Bessel-Gaussian laser beam in collisionless plasma

The objective of present work is to investigate second harmonic generation (SHG) of zeroth-order Bessel-Gaussian (B-G) laser beam in collisionless plasma. The ponderomotive force produces density gradients in plasma by expelling the plasma electrons from high field portion to low field portion thereby modifying plasma’s refractive index. This modification causes self-focusing of main beam. The density gradient further causes excitation of electron plasma wave (EPW) at the main beam frequency. The excited EPW couples with input beam thereby generating second harmonics. The well known WKB approximation and moment theory are employed for obtaining non-linear differential equation for laser beam’s spot size and expression for SHG yield. Further, numerical solutions of these equations are obtained by well known RK-4 method. It has been concluded from the present analysis that transverse component of wave parameter μ, normalized laser intensity and plasma density plays a significant role in affecting laser beam self-focusing and its SHG yield. Results from the present study are important for the laser induced plasma.

Effect of Asymmetry in the Modulation Parameters on Self-Focusing of Asymmetric Finite Airy-Gaussian Laser Beam in Collisionless Plasma

The self-focusing/defocusing of asymmetric finite Airy-Gaussian (AiG) laser beam has been investigated by employing standard Wentzel–Kramers–Brillouin (WKB) and paraxial-ray approximations in a nonrelativistic regime for underdense plasma. The second-order non-linear coupled differential equations have been solved numerically by using the fourth-order Range-Kutta method. The effect of asymmetry in the modulation parameters on the self-focusing/defocusing of the asymmetric finite AiG laser beam in collisionless plasma has been studied. It is observed that the self-focusing/ defocusing of asymmetric finite AiG laser beam is strongly connected with the initial values of the laser and plasma parameters such as modulation parameters and plasma frequency.

Domains of modulation parameter in the interaction of finite Airy–Gaussian laser beams with plasma

AbstractIn this paper, self-focusing of finite Airy–Gaussian (AiG) laser beams in collisionless plasma has been investigated. The source of nonlinearity considered herein is relativistic. Based on the Wentzel–Kramers–Brillouin (WKB) and paraxial-ray approximations, the nonlinear coupled differential equations for beam-width parameters in transverse dimensions of AiG beams have been established. The effect of beam's modulation parameter and linear absorption coefficient on the self-focusing/defocusing of the beams is specifically considered. It is found that self-focusing/defocusing of finite AiG beams depends on the range of modulation parameter. The extent of self-focusing is found to decrease with increase in absorption.

Self-focusing of cosh-Gaussian laser beam and its effect on the excitation of ion-acoustic wave and stimulated Brillouin backscattering in collisionless plasma

An analytical and numerical study has been carried out for self-focusing of an intense cosh-Gaussian laser beam in collisionless plasma and its impact on the excitation of ion-acoustic wave and stimulated Brillouin backscattering process. The analytical model has been developed under Wentzel–Kramers–Brillouin and paraxial ray approximations. The nonlinearities of ponderomotive force on electron and the relativistic oscillation of the electron mass have been used in this study. The nonlinear differential equations have been set up for the beam width parameters of the main beam, ion-acoustic wave, backscattered wave and back reflectivity of stimulated Brillouin scattering (SBS). These equations have been solved numerically for different values of decentred parameter (b), relative plasma density (ωp0/ω0) and incident laser intensity (a). The results have been compared with only relativistic nonlinearity and Gaussian profile of laser beam. The focusing of laser beam, ion-acoustic wave and scattered wave are found to be strong under relativistic-ponderomotive regime compared to only relativistic regime. Further, it is observed that focusing/intensity of main laser beam, ion acoustic wave and SBS back reflectivity increases with increasing the values of b and ωp0/ω0. Itis also found that back reflectivity of SBS process gets suppressed with the increase in the value of a. This study may be useful in laser induced fusion scheme where back scattering of SBS plays very important role.

Relativistic Self-Focusing of Hermite-cosine-Gaussian Laser Beam in Collisionless Plasma with Exponential Density Transition

This work reveals an exploration of self-focusing of Hermite-cosine-Gaussian laser beam in a collisionless plasma under relativistic nonlinearity. Self-focusing along with self-trapping of Hermite-cosine-Gaussian laser beam are analyzed for different values of laser intensity, plasma density, and decentered parameters. Mathematical analysis displays that these parameters play a major role in achieving the stronger and earlier self-focusing. Further, a comparative study between self-focusing of Hermite-cosine-Gaussian laser beam with and without exponential density ramp profile is introduced. Plasma density transition with exponential profile is found to be more effective in order to have stronger self-focusing. The present analysis may lead to very useful applications in the field of efficient harmonic generation, laser driven fusion etc.

Generation of second harmonics by a self-focused Hermite-Gaussian laser beam in collisionless plasma

In this work, the generation of second harmonics of a Hermite–Gaussian laser beam in collisionless plasma has been presented. On incidence of the Hermite–Gaussian laser beam in plasma, the charge carriers shift from the high field region to the low field region on account of the ponderomotive force which results in the generation of a transverse density gradient in the background plasma which in turn generates plasma waves at incident beam frequency ω0. Interaction of this plasma wave with the pump beam generates the second harmonics of the incident laser beam with frequency 2ω0. The moment theory approach has been used to derive the coupled differential equations for the beam widths of the laser beam in the transverse x- and y-directions which are further solved numerically. The effect of different modes and initial beam widths of the Hermite–Gaussian beam in the x- and y-directions has been investigated for the self-focusing and second harmonic yield (SHY) of the laser beam in plasma. Also, the effect of increasing plasma density is visualized on the self-focusing and SHY of the beam. It has been observed that the SHY significantly depends on different modes and initial widths of the Hermite–Gaussian laser beam as well as on plasma density.

Generation of electron plasma wave and particle acceleration by beating of two intense cross focused elliptical laser beams in collisionless plasma

This paper presents the propagation of two intense cross-focused elliptical laser beams (ELBs) in a collisionless plasma and their effect on the excitation of electron plasma waves (EPWs) and particle acceleration, when relativistic and ponderomotive nonlinearities are operative. Due to the mutual interaction of the two ELBs, cross-focusing takes place in the plasma. An EPW is generated on account of the beating of the two cross-focused ELBs of frequencies ω1 and ω2. Nonlinear differential equations have been set up for the beamwidth parameters of the ELBs, the power of the EPW and the energy gained by the electrons using WKB and paraxial-ray approximations. Numerical simulations have been carried out to investigate the effect of various laser and plasma parameters such as incident laser intensity and plasma density on the focusing of ELBs in plasmas and its effect on the power of excited EPWs and particle acceleration. Numerical results show that the focusing and intensity of both beams in plasma increase with increasing values of incident laser intensity and plasma density. It is observed that the cross-focusing of two ELBs enhances the power of generated EPWs and the yield of energy gain. This study is useful for determining the propagation dynamics of ELBs in plasma and the results are helpful for various applications requiring multiple laser beams.

Mitigation of stimulated Raman backscattering by elliptical laser beam in collisionless plasma

This paper presents theoretical and numerical study of the propagation of an elliptical laser beam in collisionless plasma with relativistic-ponderomotive nonlinearities and its effect on the excitation of electron plasma wave (EPW) and resulting stimulated Raman backscattering (SRBS) process. Nonlinear interaction between an intense elliptical laser beams with the electron plasma wave leads stimulated Raman backscattering. Following Wentzel Kramers Brillouin (WKB) and paraxial-ray approximations, non-linear differential equations for the beam width parameters of elliptical laser beam, electron plasma wave and back-scattered beam are set up and solved numerically. Numerical simulations have been carried out to investigate the effect of laser and plasma parameters on the focusing of elliptical laser beam in plasma and further its effect on the excitation of electron plasma wave and backreflectivity of stimulated Raman scattering (SRS). The focusing of an elliptical laser beam, EPW and scattered wave are reduced at higher values of laser intensity in plasma. The amplitude of excited electron plasma wave, which depends on the focusing of main laser beam and electron plasma wave reduce for higher values of incident laser intensity. The results indicate that the focusing of waves mitigates the backreflectivity of SRS. The results are also compared with only relativistic nonlinearity and the Gaussian profile of laser beam. It is observed that an elliptical laser beam mitigates the backreflectivity of SRS at higher values of laser intensity. This study is relevant to inertial confinement fusion scheme, where SRS plays very important role.

Effect of ripple on self-focusing of a cosh-Gaussian laser beam in collisionless plasma

In this paper, the effect of presence of ripple on the cosh-Gaussian beam in collisionless plasma considering relativistic nonlinearity is investigated. Using the Wentzel Kramers Brillouin (WKB) paraxial-ray approximation method and eikonal method, the basic sets of equations has been derived. It is observed that when the initial power of the ripple is greater than the critical power for self-focusing of cosh-Gaussian beam the ripple gets focused over the beam.

Stimulated Brillouin backscattering of hollow Gaussian laser beam in collisionless plasma under relativistic–ponderomotive regime

AbstractStimulated Brillouin backscattering of an intense hollow Gaussian laser beam (HGLB) from collisionless plasma has been investigated under relativistic–ponderomotive regime. The main feature of considered hollow Gaussian laser beam is having the same power at different beam orders with null intensity at the center. Backscattered radiation is generated due to nonlinear interaction between main beam (pump beam) with pre-excited ion acoustic wave (IAW). Modified coupled equations has been set up for the beam width parameters of the main beam, ion-acoustic wave, back-scattered wave, and back reflectivity of stimulated Brillouin scattering (SBS) with the help of the Wentzel–Kramers–Brillouin approximation, fluid equations and paraxial theory approach. These coupled equations are solved analytically and numerically to study the laser intensity in the plasma, the variation of amplitude of the excited IAW and back reflectivity of SBS. The back reflectivity of SBS is found to be highly sensitive to the order of the HGLB, intensity of main laser beam, and plasma density for typical laser and plasma parameters. The focusing of main laser beam (hollow Gaussian) and IAW significantly affected the back reflectivity of SBS. The results show that the self-focusing and back reflectivity is enhanced for higher order modes of HGLB.

Electron plasma wave excitation by beating of two q-Gaussian laser beams in collisionless plasma

AbstractThis paper presents a scheme for excitation of an electron-plasma wave (EPW) by beating two q-Gaussian laser beams in an underdense plasma where ponderomotive nonlinearity is operative. Starting from nonlinear Schrödinger-type wave equation in Wentzel–Kramers–Brillouin (WKB) approximation, the coupled differential equations governing the evolution of spot size of laser beams with distance of propagation have been derived. The ponderomotive nonlinearity depends not only on the intensity of first laser beam, but also on that of second laser beam. Therefore, the dynamics of one laser beam affects that of other and hence, cross-focusing of the two laser beams takes place. Due to nonuniform intensity distribution along the wavefronts of the laser beams, the background electron concentration is modified. The amplitude of EPW, which depends on the background electron concentration, is thus nonlinearly coupled with the laser beams. The effects of ponderomotive nonlinearity and cross-focusing of the laser beams on excitation of EPW have been incorporated. Numerical simulations have been carried out to investigate the effect of laser and plasma parameters on cross-focusing of the two laser beams and further its effect on EPW excitation.

Investigation of relativistic self-focusing of Hermite-cosine-Gaussian laser beam in collisionless plasma

Relativistic self-focusing of Hermite-cosine-Gaussian (HcosG) laser beam in plasma has been investigated. The distribution of HcosG laser field in the plasma is closely related to decentered parameter. The differential equation for the beam width parameter is derived by following Wentzel–Kramers–Brillouin (WKB) and paraxial approximation through parabolic wave equation approach. The behavior of beam width parameter with distance of propagation is investigated at different values of plasma density, decentered parameter and intensity parameter. Our results reveal that the laser beam is more focused at lower values of decentered and intensity parameter. Further, a strong oscillatory behavior of the beam width parameter during laser propagation in collisionless plasma is seen.

Beat wave excitation of electron plasma wave by cross-focusing of intense cosh-Gaussian laser beams in collisionless plasma with upward density ramp

This paper presents theoretical investigation of the effect of cross-focusing of two coaxial cosh-Gaussian (ChG) laser beams on beat wave excitation of electron plasma wave (EPW) in an under dense plasma with upward density ramp. The plasma wave is generated on account of beating of two coaxial laser beams of frequencies ω1 and ω2. The mechanism for laser induced nonlinearity is assumed to be a ponderomotive force. Following moment theory approach in Wentzel–Kramers–Brillouin (W.K.B) approximation nonlinearly coupled differential equations governing the evolution of spot size of the laser beams with distance of propagation have been derived. The ponderomotive nonlinearity depends not only on the intensity of first laser beam but also on that of second beam. Therefore, the behavior of first laser beam affects that of second laser beam and hence cross focusing of two laser beams takes place. By changing the decentred parameter, the peak intensity of the laser beam can be shifted in the transverse direction and a noticeable change is observed on the cross-focusing of the two laser beams as well as on the power of generated plasma wave. The results are presented in the form of graphs for typical set of laser-plasma parameters.

Second harmonic generation by self-focusing of intense hollow Gaussian laser beam in collisionless plasma

The effect of self focused hollow Gaussian laser beam (HGLB) (carrying null intensity in center) on the excitation of electron plasma wave (EPW) and second harmonic generation (SHG) has been investigated in collisionless plasma, where relativistic-ponderomotive and only relativistic nonlinearities are operative. The relativistic change of electron mass and the modification of the background electron density due to ponderomotive nonlinearity lead to self-focusing of HGLB in plasma. Paraxial ray theory has been used to derive coupled equations for the self focusing of HGLB in plasma, generation of EPW, and second harmonic. These coupled equations are solved analytically and numerically to study the laser intensity in the plasma, electric field associated with the excited EPW, and the power of SHG. Second harmonic emission is generated due to nonlinear coupling between incident HGLB and EPW satisfying the proper phase matching conditions. The results show that the effect of including the ponderomotive nonlinearity is significant on the generation of EPW and second harmonic. The electric field associated with EPW and the power of SHG are found to be highly sensitive to the order of the hollow Gaussian beam.

Stimulated Brillouin backscattering of a ring-rippled laser beam in collisionless plasma

AbstractThe effect of the propagation of a ring-rippled laser beam in the presence of relativistic and ponderomotive non-linearities on the excitation of ion-acoustic wave (IAW) and resulting stimulated Brillouin backscattering in collisionless plasma at relativistic powers is studied. To understand the nature of propagation of the ring ripple-like instability, a paraxial-ray approach has been invoked in which all the relevant parameters correspond to a narrow range around the irradiance maximum of the ring ripple. Modified coupled equations for growth of ring ripple in the plasma, generations of IAW and back-stimulated Brillouin scattering (SBS) are derived from fluid equations. These coupled equations are solved analytically and numerically to study the intensity of ring-rippled laser beam and excited IAW as well as back reflectivity of SBS in the plasma for various established laser and plasma parameters. It is found that the back reflectivity of SBS is enhanced due to the strong coupling between ring-rippled laser beam and the excited IAW. The results also show that the back reflectivity of SBS reduce for higher intensity of the laser beam.

Second Harmonic Generation of Self Focused Cosh‐Gaussian Laser Beam in Collisionless Plasma

AbstractThis paper presents an investigation of self‐focusing of a Cosh‐Gaussian (ChG) laser beam and its effect on second harmonic generation in collisionless plasma. In the presence of ChG laser beam the carriers get redistributed from high field region to low field region on account of ponderomotive force as a result of which a transverse density gradient is produced in the plasma which in turn generates an electron‐plasma wave at pump frequency. Generated plasma wave interacts with the incident laser beam and hence generates its second harmonics. Moment theory has been used to derive differential equation governing the evolution of spot size of ChG laser beam propagating through collisionless plasma. The differential equation so obtained has been solved numerically. The effect of decentered parameter, intensity of ChG laser beam and density of plasma on self‐focusing of the laser beam and second harmonic yield has been investigated. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)