scholarly journals Suppression of stimulated Brillouin scattering in laser beam hot spots

2009 ◽  
Vol 27 (4) ◽  
pp. 619-627 ◽  
Author(s):  
R.P. Sharma ◽  
Prerana Sharma ◽  
Shivani Rajput ◽  
A.K. Bhardwaj
Keyword(s):  
Laser Beam ◽  
Brillouin Scattering ◽  
Collisionless Plasma ◽  
Stimulated Brillouin Scattering ◽  
Landau Damping ◽  
Beam Radius ◽  
Plasma Parameters ◽  
Power Flux ◽  
Ion Acoustic Wave ◽  
Stimulated Brillouin

AbstractIn this article, filamentation of a high power laser beam in hot collisionless plasma is investigated considering the ponderomotive nonlinearity. We have studied the effect of self focusing (filamentation) of the laser beam on the localization of ion acoustic wave (IAW) and on stimulated Brillouin scattering (SBS) process. The nonlinear coupling between the laser beam and IAW results in the modification of the Eigen frequency of IAW; consequently, enhanced Landau damping of IAW and a modified mismatch factor in SBS process occur. Due to enhanced Landau damping, there is a reduction in the intensity of IAW wave, and the SBS process gets suppressed. For the typical laser plasma parameters: the laser power flux = 1016 W/cm2, laser beam radius (r0) = 12 µm, n/ncr = 0.11, and (Te/Ti) = 10, the SBS reflectivity is found to be suppressed approximately by 10%.

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

2015 ◽  
Vol 33 (3) ◽  
pp. 499-509 ◽  
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.

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

2014 ◽  
Vol 32 (4) ◽  
pp. 557-568 ◽  
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.

scholarly journals Study of stimulated Brillouin scattering in extended paraxial region

2012 ◽  
Vol 30 (2) ◽  
pp. 207-213 ◽  
Author(s):  
Prerana Sharma ◽  
A.K. Bhardwaj ◽  
R.P. Sharma
Keyword(s):  
Laser Beam ◽  
Brillouin Scattering ◽  
Stimulated Brillouin Scattering ◽  
Paraxial Approximation ◽  
Laser Beam Propagation ◽  
Ion Acoustic Wave ◽  
Laser Plasma Interaction ◽  
Laser Beam Profile ◽  
Axial Part ◽  
Stimulated Brillouin

AbstractThis communication presents a comparison of two cases to study the process of laser beam propagation and Stimulated Brillouin Scattering (SBS) in laser plasma interaction. These two cases are, with imposing the restriction of paraxial approximation on the laser beam and, relaxing this restriction up to a certain extent. In this work, the study done by Sharma et al. (2009) using paraxial approximation is extended by taking contribution of the off-axial rays in the laser beam profile. The spitted profile of the laser beam is obtained due to uneven focusing of the off-axial rays and its effect on localization of the ion acoustic wave (IAW) has been studied. Including the off-axial part of the laser beam semi-analytical solution of the nonlinear coupled IAW equation has been found and this is examined that off-axial part affects background densities. The nonlinear coupling between the laser beam and IAW is severely affected by modified profile of the laser beam. Further, it is investigated that the SBS is also influenced by this coupling process. Therefore, the reflectivity of SBS has been compared with and without contribution of off-axial rays. A notable change is found in the magnitude of SBS reflectivity in modified-paraxial case in comparison to the paraxial case.

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

2017 ◽  
Vol 35 (2) ◽  
pp. 226-233 ◽  
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.

scholarly journals Stimulated Brillouin backscattering of filamented hollow Gaussian beams

2013 ◽  
Vol 31 (4) ◽  
pp. 689-696 ◽  
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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