NUMERICAL SIMULATIONS OF HARMONICS GENERATION BY THE REFLECTION OF AN INTENSE LINEARLY POLARIZED LASER BEAM NORMALLY INCIDENT ON AN OVERDENSE PLASMA

摘要

We use an Eulerian Vlasov code for the numerical solution of the one-dimensional relativistic Vlasov-Maxwell equations for both electrons and ions [1, 2], and a particle-in-cell (PIC) code[3] to study the generation of harmonics in the reflection of a high intensity linearly polarized laser wave normally incident on an overdense plasma. The oscillation of the laser wave at the plasma edge creates an oscillating space-charge, giving rise to an oscillating electric field. If the intensity of the wave is sufficiently high to make the oscillation of the electrons relativistic, then the plasma edge oscillates nonlinearly in the field of the laser beam, which results in an important distortion in the reflected wave, associated with the generation of harmonics. We consider the case when the laser beam wavelength λ is much greater than the scale length of the gradient in the plasma density at the edge L_(edge) (λL_(edge)), and n/n_c =100. The two codes show general qualitative agreement for the mechanisms of harmonics generation, although some quantitative details differ somewhat.