High-intensity, short-pulse laser-solid interactions are of great importance for a number of applications and fundamental research, such as high energy density (HED) physics, laboratory astrophysics, inertial confinement fusion (ICF), particle acceleration, and ultrafast x-ray sources. X-ray spectroscopy is a powerful diagnostic tool to investigate the extreme states of matter created by these interactions. This thesis presents the development and application of x-ray spectroscopy in relativistic laser-solid interactions.
Two x-ray crystal spectrometers have been developed on the DRACO and European X-ray Free Electron Laser (XFEL) facilities for the diagnosis of dense plasmas produced by ultrashort relativistic laser pulses. A high-resolution x-ray crystal spectrometer is developed at the DRACO petawatt laser, measuring the K-shell emission spectra of Ti targets ranging from cold Kα to thermal Heα lines. This spectrometer employs a spherically bent quartz crystal and adopts Johann geometry in the dispersive plane. Geometrical analysis and ray-tracing simulations are implemented, respectively, to determine the most suitable configuration and evaluate the performance of the spectrometer, showing an excellent spectral resolution of E/δE≈15000. With the quartz spectrometer, the production and transport of hot electrons as well as the heating state in the proton acceleration Ti targets can be investigated at the DRACO petawatt laser. In addition, a multipurpose imaging x-ray crystal spectrometer is developed for the HED instrument of the European XFEL. This spectrometer is designed to measure x-rays in the energy range of 4 - 10 keV, providing high-resolution, spatially-resolved spectral measurements. A toroidally bent germanium (Ge) crystal is used, allowing x-ray diffraction from the crystal to image along a one-dimensional spatial profile while spectrally resolving along the other. A detailed geometrical analysis is performed to determine the curvature of the crystal. The theoretical performance of the spectrometer in various configurations is calculated by ray-tracing simulations. The key properties of the spectrometer, including the spectral and spatial resolution, are demonstrated experimentally on different platforms. Experimental results prove that this Ge spectrometer is a powerful tool for spatially resolved measurements of x-ray emission, scattering, or absorption spectra in high energy density physics.
The enhancement effect of a microstructured surface on laser absorption and characteristic Kα emission has been investigated by measuring K-shell emission from titanium (Ti) targets irradiated with high-intensity (~ 10^20 W/cm^2), sub-picosecond (500 fs) laser pulses. The experimental results indicate a modest enhancement (1.6x) of Kα emission from microstructured targets compared to flat foils, but with similar intensity and profile of Heα and Li-like satellites. Particle-in-cell (PIC) simulations are implemented to further understand the underlying physical processes in the laser interaction with both targets, interpreting the mechanisms responsible for the Kα enhancement. The reasons for the lower-than-expected enhancement of Kα emission are discussed. The rapid heating of the bulk plasma might result in the premature shutdown of Kα emission before the thermalization of hot electrons or even the end of laser pulses, suggesting that the use of Kα emission as a diagnostic of the hot-electron yield or relaxation could lead to a misinterpretation. This work reveals that an optimized microstructured target shows promise to produce high-brightness, quasi-monochromatic laser-driven x-ray sources for many probing applications.
While x-ray spectroscopy has been widely used for diagnosing the internal conditions of laser-produced plasmas, it is usually very challenging to extract reliable and accurate physical information from the raw x-ray spectra, especially for time- and space-integrated spectra emitting from a range of plasma conditions. In this thesis, a complex spatio-temporally resolved analysis of time- and space-integrated x-ray emission spectroscopy from the relativistic laser plasmas is presented. Particle-in-cell (PIC) simulations using the PICLS code are performed to investigate the laser-solid interaction within a picosecond (ps). The subsequent plasma evolution is simulated with the hydrodynamic code FLASH on a larger timescale (hundreds of ps). With the outputs of PIC and hydrodynamic simulations, atomic kinetics-spectroscopy simulations using the FLYCHK, SCFLY, and ATOMIC codes are performed to generate a series of synthetic spectra. These synthetic spectra are used to reconstruct a composite emission spectrum and then compared to the measured integrated spectra. A full-time evolution of electron density, temperature, and ionization state of laser plasmas is thus extracted, and verified by the comparison between the measured and simulated spectra. By this methodology, the dynamics of ultrafast relativistic laser-plasma systems was studied. The combination of x-ray spectroscopy, atomic physics, and multi-scale (i.e. PIC and hydro-) simulations is demonstrated to be a promising method to characterize the evolution of internal conditions of laser-produced plasmas. This method can also be used as an effective benchmark or reference for these numerical simulations.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:94122 |
| Date | 24 October 2024 |
| Creators | Pan, Xiayun |
| Contributors | Cowan, Thomas, Schramm, Ulrich, Neumayer, Paul, Falk, Katerina, Technische Universität Dresden, Institute of Radiation Physics, Helmholtz-Zentrum Dresden-Rossendorf |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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