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

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.

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

Laser and Particle Beams ◽

10.1017/s0263034615000555 ◽

2015 ◽

Vol 33 (3) ◽

pp. 499-509 ◽

Cited By ~ 5

Author(s):

Gunjan Purohit ◽

Priyanka Rawat

Keyword(s):

Laser Beam ◽

Narrow Range ◽

Brillouin Scattering ◽

Collisionless Plasma ◽

Plasma Parameters ◽

Ion Acoustic Wave ◽

Coupled Equations ◽

Ion Acoustic ◽

Paraxial Ray ◽

Stimulated Brillouin

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.

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Enhanced Brillouin scattering of gaussian laser beam in collisional plasma: Moment theory approach

Journal of Nonlinear Optical Physics & Materials ◽

10.1142/s0218863514500118 ◽

2014 ◽

Vol 23 (01) ◽

pp. 1450011 ◽

Cited By ~ 10

Author(s):

Keshav Walia

Keyword(s):

Acoustic Wave ◽

Laser Beam ◽

Pump Beam ◽

Brillouin Scattering ◽

Scattered Wave ◽

Theory Approach ◽

Gaussian Laser Beam ◽

Moment Theory ◽

Ion Acoustic Wave ◽

Ion Acoustic

In the present paper, enhanced Brillouin scattering of a gaussian laser beam in a collisional plasma has been investigated with the help of moment theory approach. The pump wave (ω0, k0) interacts with pre-excited ion-acoustic wave (ω, k), thereby generating a back-scattered wave (ω0 - ω, k0 - k). As a specific case, back scattering for which k ≃ 2k0 has been discussed. Due to nonuniform heating, collisional nonlinearity arises, which leads to redistribution of carriers. As a result background plasma density profile in a direction transverse to pump beam axis is modified. Consequently, the pump beam becomes self-focused and in turn leads focusing of ion-acoustic wave and back-scattered wave under appropriate conditions. It is further observed from the analysis that focusing of waves greatly enhances the SBS back-reflectivity.

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Effect of self-focused rippled laser beam on the excitation of ion acoustic wave in relativistic ponderomotive regime

Laser and Particle Beams ◽

10.1017/s0263034614000512 ◽

2014 ◽

Vol 32 (4) ◽

pp. 557-568 ◽

Cited By ~ 3

Author(s):

Rakhi Gauniyal ◽

Prashant Chauhan ◽

Priyanka Rawat ◽

Gunjan Purohit

Keyword(s):

Acoustic Wave ◽

Laser Beam ◽

Collisionless Plasma ◽

Plasma Parameters ◽

Power Flux ◽

Ion Acoustic Wave ◽

Coupled Equations ◽

Increase With Increase ◽

Ion Acoustic ◽

Paraxial Ray

AbstractThis paper presents an investigation of self-focusing of intense Gaussian rippled laser beam in collisionless plasma by including the nonlinearity associated with the relativistic mass and the ponderomotive force and its effects on the excitation of ion acoustic wave. The growth of ripple, riding on an intense Gaussian laser beam in plasma and its coupling with ion acoustic wave has also been studied. Modified coupled equations for main laser beam, growth of laser ripple in plasma, rippled laser beam, beam width, and density perturbation associated with ion acoustic wave are derived using Wentzel-Kramers-Brillouin and paraxial ray approximation. These coupled equations are solved analytically and numerically to study the laser intensity in plasma and the variation of amplitude of the ion acoustic wave for various established laser and plasma parameters. From numerical computation, it is observed that both nonlinearities significantly affected the dynamics of the growth of laser ripple in plasma, propagation of rippled laser beam as well as ion acoustic wave in plasma at high laser power flux. The growth of laser ripple increase with increase in the intensity of laser beam and due to the contribution of growth rate, intensity profile of rippled laser beam and ion acoustic wave modified accordingly.

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Excitation of nonlinear ion acoustic wave and stimulated Brillouin scattering of hollow Gaussian beam in relativistic plasma

Laser and Particle Beams ◽

10.1017/s0263034617000088 ◽

2017 ◽

Vol 35 (2) ◽

pp. 226-233 ◽

Cited By ~ 1

Author(s):

P. Sharma

Keyword(s):

Differential Equation ◽

Acoustic Wave ◽

Gaussian Beam ◽

Brillouin Scattering ◽

Collisionless Plasma ◽

Stimulated Brillouin Scattering ◽

Beam Width ◽

Ion Acoustic Wave ◽

Ion Acoustic ◽

Stimulated Brillouin

AbstractIn the present work, excitation of nonlinear ion acoustic wave (IAW) in collisionless plasma by laser beam having null intensity at the center is examined considering relativistic nonlinearity. The differential equation for beam-width parameter is determined considering relativistic nonlinearity using the paraxial and Wentzel–Kramers–Brillouin approximations by the parabolic equation method. The propagation features of the IAW are found to be modified due to the nonlinearity present in the system. The hollow Gaussian beam (HGB) gets nonlinearly coupled with the seed IAW, results in excitation of nonlinear IAW. The interaction of nonlinear IAW with pump beam demonstrated stimulated Brillouin scattering (SBS) of HGB. It is found that the power of IAW and power of SBS is affected with the order of HGB. The power of IAW and backscattered power of SBS is determined analytically and numerically for various orders of HGB. It is found that the power of IAW and the backscattering is diminished for higher order of HGB.

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Self-focusing of Gaussian laser beam in collisionless plasma and its effect on stimulated Brillouin scattering process

Optics Communications ◽

10.1016/j.optcom.2012.10.063 ◽

2013 ◽

Vol 290 ◽

pp. 175-182 ◽

Cited By ~ 17

Author(s):

Arvinder Singh ◽

Keshav Walia

Keyword(s):

Laser Beam ◽

Brillouin Scattering ◽

Collisionless Plasma ◽

Stimulated Brillouin Scattering ◽

Scattering Process ◽

Gaussian Laser Beam ◽

Self Focusing ◽

Stimulated Brillouin

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Stimulated Brillouin backscattering of filamented hollow Gaussian beams

Laser and Particle Beams ◽

10.1017/s0263034613000670 ◽

2013 ◽

Vol 31 (4) ◽

pp. 689-696 ◽

Cited By ~ 10

Author(s):

R.P. Sharma ◽

Ram Kishor Singh

Keyword(s):

Acoustic Wave ◽

Gaussian Beam ◽

Brillouin Scattering ◽

Collisionless Plasma ◽

Stimulated Brillouin Scattering ◽

Ion Acoustic Wave ◽

Ion Acoustic ◽

Paraxial Ray ◽

Stimulated Brillouin ◽

Plasma Coupling

AbstractThis paper presents an investigation for excitation of ion acoustic wave and resulting stimulated Brillouin scattering in a collisionless plasma due to presence of a laser beam carrying null intensity at center (hollow Gaussian beam). In presence of ponderomotive nonlinearity, the pump beam get focused and affects the back stimulated Brillouin scattering process. To understand the nature of laser plasma coupling, a paraxial-ray approximation has been invoked for the propagation of the hollow Gaussian beam, ion acoustic wave, and stimulated Brillouin scattering. It is observed from the result that self-focusing and back reflectivity reduces for higher order of hollow Gaussian beam.

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