Study of radiative shocks in the context of laboratory astrophysics ; Étude des chocs radiatifs dans le cadre de l'astrophysique de laboratoire

The development of lasers for several decades now allows to concentrate a macroscopic quantity of energy (around ;1 kJ) in a small volume (a few mm3) and over a short duration (around 1 ns). This defines the High Energy Densities (HED) regime, that can be found in planet's core or inside stellar systems. Laboratory Astrophysics is the frame of this thesis, which consists of performing experiments in the laboratory with high-energy lasers. Coupled with scaling laws, experiments results can be used to model dedicated astrophysical phenomena. The experimental parameters that are measured can be extended to the reproduced astrophysical system. During this thesis, we focused on a specific type of phenomenon: radiative shocks. These are present for example during supernova explosions, around molecular clouds, or in accretion disks.We first study the experimental aspect of the radiative shock generated by high energy lasers, especially at the GEKKO laser facility in Osaka (Japan). In particular, we determine the criteria that must be considered to qualify a shock as a "radiative" shock, then we study the experimental constraints that make it possible to generate it, which requires an important work of numerical simulation.Afterwards, we expose different aspects of the interaction between a radiative shock and a solid obstacle, reproducing the ablation of a molecular cloud by massive stars in its neighbouhood. We present theoretical, numerical and experimental aspects.Another effect that has been found experimentally, then explained analytically and numerically, is the deceleration of a shock when radiative effects are significant. This leads to instabilities developments, like in SN1987A supernova circumstellar medium. The model developed gives a possible explanation on the evolution of hotspots observed in the circumstellar medium.Finally, in order to study these effects experimentally for a shock with higher radiative effects, we present in this thesis the design of a Laser MegaJoule (LMJ) experiment that will take ...