A simple device for the production and study of cylindrical shock waves, based on the sliding discharge mechanism, is described. Initial gas pressures of up to several hundred torr and line source energies from below 1 J cm-1 up to above 10 J cm-1 can be applied. Interferometric measurements carried out on shock waves produced by line source energies of 1.8 J cm-1 have yielded information on the initial ionisation of the gas ( approximately 5%), on the compression of the shock front ( approximately 3.5 rho 0) during the early stages and on its velocity as a function of the radius. Good agreement was found with numerical calculations of cylindrical shock waves.
Rapid (100 ps) voltage oscillations have been observed in a capacitively coupled target irradiated with 3.5 ns pulses of Nd-YAG light at irradiances of between 5*1012 and 2*1015 W cm-2 on a 40 mu m spot. The measurements were made using a fast (40 ps rise-time) Pockels cell intercepting a diagnostic light pulse to a streak camera. The oscillations were found to depend on the spot size and the shape of the laser pulse. The oscillation frequencies found (up to 12 GHz) were too low to correspond to plasma instabilities. Double layers and plasma turbulence are proposed as the cause of the voltage oscillations.
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