TY - JOUR

T1 - Growth of spike in relativistic Gaussian laser beam in a plasma and its effect on third-harmonic generation

AU - Ahmad, N.

AU - Mahmoud, S. T.

AU - Purohit, G.

N1 - Funding Information:
The author Andre Luis Ribeiro Ribeiro is grateful to the CAPES foundation , Ministry of Education of Brazil, for funding his scholarship (grant no. 0698130 ).
Publisher Copyright:
Copyright © Cambridge University Press 2017.

PY - 2017/3/1

Y1 - 2017/3/1

N2 - A paraxial ray formalism is developed to study the evolution of an on axis intensity spike on a Gaussian laser beam in a plasma dominated by relativistic and ponderomotive non-linearities. Ion motion is taken to be frozen. A single beam width parameter characterizes the evolution of the spike. The spike introduces two competing influences: diffraction divergence and self-convergence. The former grows with the reduction in spot size of the spike, while the latter depends on the gradient in non-linear permittivity. Parameter δ = (ωp r 00/c) a 00/(3.5 r 00/r 01) characterizes the relative importance of the two, where r 01 and r 00 are the spike and main beam radii, ωp is the plasma frequency, and a 00 is the normalized laser amplitude. For δ > 1, the intensity ripple causes faster self-focusing of the beam; higher the ripple amplitude stronger the focusing. In the opposite limit, diffraction divergence increases more rapidly, slowing down the self-focusing of the beam. As the beam intensity rises due to self-focusing, it causes stronger generation of the third harmonic.

AB - A paraxial ray formalism is developed to study the evolution of an on axis intensity spike on a Gaussian laser beam in a plasma dominated by relativistic and ponderomotive non-linearities. Ion motion is taken to be frozen. A single beam width parameter characterizes the evolution of the spike. The spike introduces two competing influences: diffraction divergence and self-convergence. The former grows with the reduction in spot size of the spike, while the latter depends on the gradient in non-linear permittivity. Parameter δ = (ωp r 00/c) a 00/(3.5 r 00/r 01) characterizes the relative importance of the two, where r 01 and r 00 are the spike and main beam radii, ωp is the plasma frequency, and a 00 is the normalized laser amplitude. For δ > 1, the intensity ripple causes faster self-focusing of the beam; higher the ripple amplitude stronger the focusing. In the opposite limit, diffraction divergence increases more rapidly, slowing down the self-focusing of the beam. As the beam intensity rises due to self-focusing, it causes stronger generation of the third harmonic.

KW - Gaussian laser beam

KW - Harmonic generation

KW - Non-linear plasma physics

KW - Paraxial theory

KW - Self-focusing

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U2 - 10.1017/S0263034616000902

DO - 10.1017/S0263034616000902

M3 - Article

AN - SCOPUS:85010899673

SN - 0263-0346

VL - 35

SP - 137

EP - 144

JO - Laser and Particle Beams

JF - Laser and Particle Beams

IS - 1

ER -