Ionization dynamics in relativistic laser plasma

This work presents a novel resonance X-ray diagnostic method for hot dense plasma with femtosecond temporal resolution. In particular, I was able to show that the Cu 21+ ionization state in relativistic laser-matter interaction with 1021 W/cm2 intensity is strongly localized in depth to less than a micrometer. This precision allows to reveal disagreements with state-of-the-art particle-in-cell simulations. Experimentally, I employed the combination of a relativistic femtosecond laser and a free-electron X-ray laser (XFEL), enabling synchronous excitation and probing of the plasma. Emission spectroscopy and X-ray imaging were employed for the selective study of the temporal and spatial evolution of ionization states. My results will allow to improve the understanding of these laser-matter-interactions and implementation of currently lacking processes into simulations.:1 Introduction 1.1 Background and Motivation 1.2 Objectives of the Thesis 1.3 Structure of the Thesis 2 European XFEL and Relativistic Laser 2.1 European XFEL 2.1.1 Synchrotron Radiation 2.1.2 Undulator 2.1.3 X-FELs 2.1.4 European XFEL 2.2 ReLaX – Relativistic Laser at XFEL 2.2.1 Chirped-Pulse Amplification 2.2.2 ReLaX – Details and parameters 2.3 Synchronization of XFEL X-ray Pulses and ReLaX Laser Pulses 2.3.1 Challenges in Temporal Synchronization 2.3.2 The RF Master Timer System 2.3.3 The Cross-Correlation Method, Photon Arrival Monitor, Zero-Timing 3 Fundamental Aspects of Laser-Induced Plasma in Femtosecond Laser–Matter Interaction 3.1 Plasma theory – Hot and Dense plasma regime 3.1.1 Essential Plasma Parameters 3.1.2 Dense Plasma Regimes: Hot Dense Plasma and Warm Dense Plasma 3.2 Femtosecond laser plasma 3.2.1 Structure of a Femtosecond Laser Pulse 3.2.2 Dielectric Permittivity of Plasma and Critical Density 3.2.3 Interaction of laser prepulse with target. Preplasma 3.2.4 Laser Field Ionization 3.2.5 Absorption Mechanisms for Laser Pulses 3.2.6 Hot Electrons Generation 3.2.7 Stages of Femtosecond Plasma Generation 3.3 X-Ray Emission Generation in Laser Plasma, Ionization Distribution 3.3.1 Bremsstrahlung Radiation 3.3.2 Characteristic X-Ray generation 3.4 Relaxation and Recombination 3.4.1 Collisional Relaxation 3.4.2 Heat Transfer Processes 3.4.3 Adiabatic Expansion 3.4.4 Plasma Recombination 3.5 X-Ray Methods in Plasma Research 3.5.1 X-ray Emission Spectroscopy (XES) 3.5.2 Resonant Inelastic X-ray Scattering (RIXS) 3.5.3 X-ray Absorption Spectroscopy (XAS) 3.5.4 Small-Angle X-ray Scattering (SAXS) 3.5.5 X-ray Diffraction (XRD) 3.5.6 X-ray Thomson Scattering (XRTS) 4 Resonant X-Ray Emission Spectroscopy of Specific Ionization States 4.1 X-ray Resonant Probing 4.1.1 Principle of X-ray Resonant Probing 4.1.2 Efficiency of Resonant Absorption 4.2 Targets 4.3 High-Resolution X-ray Spectroscopy for HED Instrument 4.3.1 Bragg Spectroscopy: Von Hámos Geometry 4.3.2 Jungfrau detectors 4.3.3 Technical concept 4.4 Experimental setup 4.5 Spectrum processing and Results 4.6 Conclusions 5 Absorption Imaging of X-Ray Resonant Pumping 5.1 X-Ray Imaging with XFEL 5.1.1 Using XFEL for X-ray Imaging 5.1.2 Phase Contrast Imaging 5.1.3 The Complex Refractive Index in X-ray Optics 5.1.4 Implementation of Phase Contrast Imaging 5.1.5 Propagation-Based Imaging Scheme 5.2 Compound Refractive Lenses 5.3 Experimental Setup 5.4 Image processing and results 5.5 Conclusions 6 Simulations of X-Ray Resonant Probing and Results Discussion 6.1 Methods for Modeling the Interaction of Laser Radiation with Matter 6.1.1 Static models 6.1.2 Hydrodynamics Models 6.1.3 Kinetic Models 6.1.4 Particle-In-Cell (PIC) method 6.1.5 Atomic Codes 6.1.6 Hybrid Codes 6.2 Opacity spectra calculated with FLYCHK 6.3 PIC-simulations of Laser-Plasma Interaction 6.4 Imaging Calculations with Simulated Resonant Opacities 6.5 Results discussion 7 Summary and Outlook 7.1 Summary 7.2 Outlook Bibliography Acknowledgments