Session kWeaP3 - Poster Session: Laser-Plasma Interactions.
POSTER session, Wednesday morning, November 19
South Hall, Convention Center
We report on experiments performed at the Rutherford Appleton Laboratory with the Vulcan CPA laser (30J, 1ps, 1.054 \mum) focussed to 10^18-10^19 Wcm^-2 at 30^o incidence angle on a plastic target(thickness 140 to 250 \mum). The prepulse intensity was measured to be 10^-6. Interferomtry, polarimetry and shadowgraphy was used to diagnose the ablated plasma with a transverse 1 ps, frquency doubled (527 nm), low power laser probe. The observations show:(i) the electron density distribution in the ablated plasma has a minimum along the target normal similar to the observation by Atwood et al.[1]: this minimum ascribed to the laser pondermotive force;in our experiment the minimum was found to persist long after the laser pulse (> 1 ns);(ii) the polarimeter failed to detect any Faraday rotation which indicates that any azimuthal magnetic field, if generated, was about 2 MG; (iii) plasma was observed on the rear surface of the target; the earliest time at which this plasma was observed was at 22 ps for a 140 \mum thick CD_2 target localised exactly in line with the laser focus on the front surface; this plasma is consistent with it being generated by fast electron penetration into the sold target in agreement with Monte-Carlo simulations [2]. [1] D.T. Atwood et al., Phys. Rev. Lett. \bf40, 184 (1978). [2] J.R. Davies et al., submitted to Phys. Rev. E