Research Paper: Laser Self-focusing Effect on Collisional Quantum Plasma with Ramped Density Profile

Document Type : Research Paper

Author

Assistant Professor, Photonics and Quantum Technology Research School, Nuclear Science and Technology Research Institute, Tehran, Iran.

Abstract

When an intense laser beam propagates in plasma, due to relativistic electrons resulting from the laser electric field, the plasma refractive index alters. Subsequently, the plasma behaves initially similar to a positive lens that decreases the laser spot size. In this article, the propagation of the laser beam in collisional quantum plasmas is investigated with considering a ramped density profile. Using WKB and paraxial approximations through parabolic equation, a mathematical formulation for the beam width parameter is obtained from the wave equation. Acquired equations are numerically solved by employing the fourth-order Runge-Kutta method. In the collisionless plasma, by increasing the ramp slope, the beam width focuses with less oscillation amplitude, smaller laser spot size and more oscillations. In the collisional quantum plasma, due to energy absorption, the oscillation amplitude enhances by passing through the plasma and the laser beam defocuses at a few lengths. For the greater values of the slope and the collision frequency, the laser spot size oscillates with the higher amplitude and defocuses in a shallower plasma depth. Also, greater plasma density results in smaller laser spot size and bigger oscillation frequency. Then, this effect is compared in the strong and weak quantum and classical plasmas. Decreasing the plasma temperature improves the magnetization due to the ponderomotive force related to the time variation, the beam-width oscillates with greater frequency and deeper penetration in the strong quantum plasma in comparison with the weak quantum or the classical cases.

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References

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  • Receive Date: 04 September 2020
  • Revise Date: 16 October 2020
  • Accept Date: 20 December 2020

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