The development of second-generation short-pulse laser-driven radiation sources requires a mature understanding of the relativistic laser-plasma processes as e.g. plasma oscillations, heating and transport of relativistic electrons as well as the development of plasma instabilities. These dynamic effects occurring on femtosecond and nanometer scales are very difficult to access experimentally.
In a first experiment in 2014 at the Matter of Extreme Conditions facility at LCLS we demonstrated that Small Angle X-ray Scattering (SAXS) of femtosecond x-ray free electron laser pulses is able to make these fundamental processes accessible on the relevant time and length scales in direct in-situ pump-probe experiments [Kluge et al., Phys. Rev. X 8, 031068 (2018)]. Here we report on a recent follow-up experiment with significantly higher pump intensity reaching the relativistic intensity domain, improved targetry, XFEL shaping and particle diagnostics. We give an overview of the new capabilities in combining a full suite of particle and radiation diagnostics including ion-, electron-, bremsstrahlung- and K-alpha-spectrometer, proton beam profile imager and SAX scattering. Especially probing at resonant x-ray energies can give new insight into the ultra-fast ionization processes, plasma opacity and equation-of-state in non-equilibrium plasmas.
Respresenting the collaborations of the latest two MEC SAXS experiments we will give an overview of the experimental setup and the technical implementation of radiation and particle diagnostics as well as imaging methods. We will exemplify the capabilities on the specific example of probing the correlation of thin layers under high-intensity laser irradiation and its consequences for modelling the heating of buried layers and rear surface expansion.