Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

We present high-resolution spectroscopic measurements of the optically thick hydrogen-like Al Ly-α line shape from a cylindrically expanding plasma. The cylindrical expansion is produced by symmetrically irradiating a 120 μm diameter coated wire target with six beams of the VULCAN Nd:glass laser at an irradiance of 2×1014Wcm-2. Small shifts in the line position and changes in the line shape can be attributed to radiation emitted from different regions of the plasma and passing through different gradients in plasma density, temperature, and velocity. The experimental profiles are compared to a time-dependent hydrodynamics code incorporating a Sobolev escape probability treatment of the radiative transport. © 2000 Elsevier Science B.V.

Abstract:

Fast electron generation and propagation were studied in the interaction of a green laser with solids. The experiment, carried out with the LULI TW laser (350 fs, 15 J), used [Formula Presented] emission from buried fluorescent layers to measure electron transport. Results for conductors (Al) and insulators (plastic) are compared with simulations: in plastic, inhibition in the propagation of fast electrons is observed, due to electric fields which become the dominant factor in electron transport. © 2000 The American Physical Society.

Abstract:

We analyze recent experimental results on the increase of fast electron penetration in shock compressed plastic [Phys. Rev. Lett. 81, 1003 (1998)]. It is explained by a combination of stopping power and electric field effects, which appear to be important even at laser intensities as low as [Formula Presented] An important conclusion is that fast electron induced heating must be taken into account, changing the properties of the material in which the fast electrons propagate. In insulators this leads to a rapid insulator to conductor phase transition. © 2000 The American Physical Society.

Abstract:

The results of a study of the channeling of intense picosecond laser pulses by a discharge-ablated capillary waveguide are presented. The peak-energy transmission for a 10-mm-long waveguide is measured to be 65% for an input intensity of 1 × 10¹⁶ W cm^-2. The importance of inverse bremsstrahlung, stimulated Raman scattering, stimulated Brillouin scattering, atomic modulation instabilities, and ionization of the discharge plasma as loss mechanisms for both intense femtosecond and picosecond pulses are considered. © 2000 Optical Society of America.