Anisotropic heating and magnetic field generation due to Raman scattering in laser-plasma interaction*

The interaction of intense electromagnetic waves with plasmas is a rich research topic. Magnetic fields play a crucial role in this context and there are several processes that can lead to the generation and amplification of these fields. Recent experiments, for instance, demonstrated the generation of large-scale magnetic fields due to hot electron currents in underdense plasmas and determined the turbulent dynamics of intense magnetic fields in laser-solid interactions. 
In this work, we explore a novel mechanism to drive the Weibel instability in laser-plasma interactions. Using two and three-dimensional particle-in-cell simulations with OSIRIS, we show that in sub-quarter-critical density plasmas, Raman scattering will heat the plasma preferably in the direction of the scattered plasma waves, creating a temperature anisotropy behind the laser. The direction of the scattered waves has a dependence on the plasma temperature, as Landau damping can prevent small wavelength waves to grow. We find a good match between the observed magnetic fields and the theoretical predictions of the Weibel instability due to temperature anisotropy.