The evolution of a shock wave pressure induced by a laser pulse in a liquid filled thin tube using the background-oriented schlieren technique

We investigate an angular variation of pressure at a laser-induced shock front in a liquid filled thin tube. We adopt the background-oriented schlieren (BOS) technique. This technique enables us to measure twoor three-dimensional pressure field in a small region with a simple setup. We obtain the spatiotemporal evolution of the pressure field thanks to an ultra high-speed video camera and a laser stroboscope. Remarkably, although shape of the shock wave is like a sphere, we find an angular variation of the pressure at the shock front. The maximum pressure is at the region in the direction of the laser shot. It is about four times higher than that in the perpendicular direction. Pressure measured by BOS technique are compared with those obtained by another method. Our results might be used for efficient generation systems of the microjet which can be applicable for needle free injection devices.