Modeling of laser ponderomotive self-focusing in plasma within the Paraxial Complex Geometrical Optics approach

A. Ruocco (1) , G. Duchateau (1) , V. Tikhonchuk (1) , Stefan Hüller (2)

1 CELIA - Centre d'Etudes Lasers Intenses et Applications
2 CPHT - Centre de Physique Théorique [Palaiseau]

Laser ponderomotive self-focusing in an underdense homogeneous plasma is studied within the Paraxial Complex Geometrical Optics (PCGO) approach implemented in a hydrodynamic code in 2D planar geometry. The self-focusing of a PCGO Gaussian beam is compared to simulations performed with a paraxial electromagnetic code. Good agreement has been found for beam powers less than three times the critical power and for plasma densities 5%-10% of the critical density. Besides Gaussian beams, PCGO allows to reproduce spatially modulated beams by superposition of Gaussian beams, mimicking a speckle pattern. Although the statistics of speckle patterns generated with PCGO reproduces well the speckle statistics of optically smoothed beams, a PCGO speckle is larger than optical speckles, carrying thus higher power such that they overestimate self-focusing effects. To overcome this issue, an algorithm is proposed within PCGO framework: it consists of superposing several Gaussian beams forming a speckle such that self-focusing effects are eventually well controlled. It is found that the superposition of three Gaussian beams with appropriate initial conditions leads to a reduction of the PCGO speckle intensity enhancement.

Mots clés: hydrodynamics codes; laser-plasma interaction; inertial confinement fusion; beam self-focusing

Domaines: Physique [physics]; Physique des plasmas [physics.plasm-ph]

A. Ruocco, G. Duchateau, V. Tikhonchuk, Stefan Hüller. Modeling of laser ponderomotive self-focusing in plasma within the Paraxial Complex Geometrical Optics approach. Plasma Physics and Controlled Fusion, 2019, Plasma Physics and Controlled Fusion, 61 (115009), ⟨10.1088/1361-6587/ab467b⟩. ⟨hal-02289443⟩