Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

Measurements of magnetic fields generated during ultrahigh intensity (>10 19Wcm -2), short pulse (0.7-1 ps) laser-solid target interaction experiments are reported. An innovative method is used and the results are compared with particle-in-cell simulations. It is shown that polarization measurements of the self-generated harmonics of the laser can provide a convenient method for diagnosing the magnetic field - and that the experimental measurements indicate the existence of peak fields greater than 340 MG and below 460 MG at such high intensities. In particular, the observation of the X-wave cutoffs and the observed induced ellipticity of the harmonics can provide a reliable method for measuring these fields. These observations are important for evaluating the use of intense lasers in various potential applications and perhaps for understanding the complex physics of exotic astrophysical objects such as neutron stars. © 2002 American Institute of Physics.

Abstract:

The generation of harmonics from the interaction of an intense (I ≥ 1018 W cm-2) laser with a solid surface was discussed. At higher laser intensities, the modulation of the harmonic emission spectrum with a periodicity of two to four harmonics was observed. The results showed that the dynamics of the critical surface can be inferred from the shape of the harmonic spectrum.

Abstract:

In this paper we present an analysis of Thomson scattered light from an arc plasma jet. Our approach goes beyond the standard random-phase approximation (RPA) and provides more consistent data for the electron temperature and density in plasmas that are weakly nonideal and collisional. The theory is based on a memory function formalism for the spectral density function with the use of the three lowest-order frequency-moment sum rules. These moments are then corrected for temperature inhomogeneities in the scattering volume. The proposed interpretation of scattering data is compared with the RPA result and with the standard Bhatnagar-Gross-Krook collisional model for the dynamic structure factor. It is shown that the obtained electron temperature values are closer but not equal to local thermodynamic equilibrium temperature values extracted from spectroscopic measurements.