Laser-induced shock waves in PMMA confined foils

Confined ablation experiments were performed to measure pulsed laser-induced shock wave profiles in aluminum and copper foils by using polyvinylidene fluoride (PVDF) gauges. The aluminum and copper targets of 40–200 μm thickness were irradiated by neodymium laser at 1.06 μm wavelength and at a pulse width of 33 ns (FWHM, full-width at half-maximum) at a power density around 0.45 G W/cm2. A 3 mm thick polymethyl methacrylate (PMMA) overlay was used to confine the target. Experimental measurements revealed the dependence of the laser-induced shock pressure on the thickness and material properties of the target. It was found that attenuation of peak pressure of the laser-induced shock waves could be well fitted by a power-form function PM=P0X−n. Here, n is a parameter relevant to material properties, P0 is the pressure when X=1 and PM is the maximum pressure at X, the propagation distance of the shock wave from the front surface of the target. A simplified analytical description is presented to illustrate the features of the shock profiles obtained from experiments. The space–time diagram of wave propagation and the successive pressure states were determined from which theoretical pressure time profiles were constructed. Both the experiment and theoretical analysis inferred a shock pressure of 4.5–5.5 kbar in the target. Some direct ablation experiments were also conducted to evaluate the enhancement of pressure for PMMA confinement. By comparison with direct ablation, confined ablation can increase the pressure by 7.5–11.8 times. The study provides the data for the PMMA-confined targets.