Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

We report the first systematic observations of relativistic self-phase-modulation (RSPM) due to the interaction of a high intensity laser pulse with plasma. The plasma was produced in front of a solid target by the prepulse of a 100 TW laser beam. RSPM was observed by monitoring the spectrum of the harmonics generated by the intense laser pulse during the interaction. The multipeaked broadened spectral structure produced by RSPM was studied in plasmas with different density scale lengths for laser interactions at intensities up to 3.0×[formula presented] [formula presented] [formula presented] The results are compared with calculated spectra and agreement is obtained. © 2002 The American Physical Society.

Abstract:

The construction of short pulse (<200 fs) tunable X-ray laser sources based on the X-ray free electron laser (XFEL) concept will be a watershed for plasma-based and warm dense matter research. These new fourth generation light sources will have extremely high fields and short wavelengths (&SIM;0.1 nm) with peak spectral brightnesses 10(10) greater than third generation sources. Further, the high intensity upgrade of the GSI accelerator facilities will lead to specific energy depositions up to 200 kJ/g and temperatures between 1 and 10 eV at almost solid-state densities, enabling interesting experiments in the regime of nonideal plasmas, such as the evolution of intense ion beams in the interior of a Jovian planet. Below we discuss several applications: the creation of warm dense matter (WDM) research, probing of near solid density plasmas, and laser-plasma spectroscopy of ions in plasmas. The study of dense plasmas has been severely hampered by the fact that laser-based methods have been unavailable and these new fourth generation sources will remove these restrictions.

Abstract:

We present detailed spectroscopic analysis of the primary K-shell emission lines from a uniaxially expanding laser-produced hydrogenic and heliumlike aluminum plasma. The spectroscopic measurements are found to be consistent with time-dependent hydrodynamic properties of the plasma, measured using Thomson scattering and shadowgraphy. The K-shell population kinetics code FLY with the measured hydrodynamic parameters is used to generate spectra that are compared to the experimental spectra. Excellent agreement is found between the measured and calculated spectra for a variety of experimental target widths employed to produce plasmas with different optical depths. The peak emission from the hydrogenic Lyman series is determined to be from a temporal and spatial region where the hydrodynamic parameters are essentially constant. This allows a single steady-state solution of FLY to be used to deduce the electron temperature and density, from the measured line ratios and linewidths, for comparison with the Thomson and shadowgraphy data. These measurements are found to agree well with time-dependent calculations, and provide further validation for the FLY calculations of the ionization and excitation balance for a K-shell aluminum plasma. We also discuss the possible application of this data as a benchmark for hydrodynamic simulations and ionization/excitation balance calculations. © 2002 The American Physical Society.