Introduction to laser-plasma interactions*

Laser-plasma interactions (LPI) dictate how intense laser beams propagate, deposit their energy and potentially drive parametric instabilities in inertial confinement fusion (ICF) experiments [1]. In this tutorial, we will provide a simple introduction to the essential LPI processes relevant to ICF, i.e., in the “long” pulse (nanosecond-scale) regime, emphasizing the intuitive physical pictures of the various processes at play over their detailed mathematical description.

We will begin with the description of the linear propagation and absorption of light waves in plasmas, before introducing the ponderomotive force, which is the primary mechanism at the origin of most nonlinear processes relevant to ICF. The second part of the talk will introduce nonlinear phenomena, beginning with “self-action” effects (self-focusing and beam deflection) and following up with an introduction to all three-wave instabilities in laser-plasmas. These include Raman or Brillouin scattering, two-plasmon decay and crossed-beam energy transfer, which all play a crucial role in ICF experiments.

Finally, the last part of the presentation will present some of the nonlinear saturation mechanisms for parametric instabilities, such as secondary instabilities and kinetic effects (“kinetic inflation”).

The target audience for this talk will be students and researchers new to the field of LPI.

[1] “Introduction to laser-plasma interactions”, P. Michel (Springer, 2023)