On parallel laser beam merger in plasmas

Self-focusing instability is a well-known phenomenon of nonlinear optics, which is of great importance in the field of laser-plasma interactions. Self-focusing instability leads to beam focusing and, consequently, breakup into multiple laser filaments. The absolute majority of applications tend to avoid the laser filamentation regime due to its detrimental role on laser beam profile and peak intensity. In our work, using particle-in-cell simulations and a nonlinear Schrodinger equation solver, we address the problem of the interaction of multiple parallel beams in plasmas. We consider both non-relativistic and moderately relativistic regimes and demonstrate how the physics of parallel beam interaction transitions from the familiar self- and mutual-focusing instabilities in the non-relativistic regime to moderately relativistic regime, where an analytical description of filament interaction is impenetrable.