Laser driven shock wave studies in gold coated Plexiglas targets

Abstract

Laser-driven shock wave propagation in a transparent material such as Plexiglas coated with a thin overlayer of gold is studied using the technique of high speed optical shadowgraphy. A Nd: glass laser was focussed to produce intensities in the range of 10′²-10′⁴W/cm² on the target, within an irradiation spot diameter of 160 pm, optical shadowgrams were recorded bya second harmonic (0.53 pm wavelength) pulse. Shock pressures and scaling of pressure with laser intensity was studied. Shock pressures in gold-coated Plexiglas target was observed to be considerably higher compared to those in uncoated targets. This enhancement of shock pressure has been explained on the basis of contribution of an X-ray driven ablative heat wave in the gold plasma. Shock pressure values show a close agreement with those obtained from a one-dimensional Langrangian hydrodynamic simulation. Shadowgrams of shock fronts produced by non-uniform spatial laser beam irradiation profiles have shown complete smoothing when a gold layer is used on a Plexiglas target.