Frontal and tilted PDV probes for measuring velocity history of laser-shock induced calibrated particles

Photonic Doppler Velocimetry (PDV, also known as LDV or HetV) is a remarkable tool for measuring the different velocities of many objects simultaneously, including tiny individual reflectors such as particles ejected by the rear face of a metallic plate damaged by a shock. This paper presents simplified experiments in which calibrated particles are accelerated and observed with PDV. They were shock-loaded using a pulsed laser (0.7 J, 10 ns, 532 nm) resulting in an acceleration up to 100 m/s. Various experiments have been performed to study the influence of different particle parameters: the material (Cu, Al), the size (10 to 200 micrometers) and the shape (sphere or rods). We recorded the back-reflected light with both orthogonal and tilted probes, and present the corresponding PDV spectrograms displaying cloud velocities as well as velocity tracks due to single particles. All of them decelerate within the ambient gas, while some rods also rotate. By applying simple models of deceleration and rotation, we try to retrieve their sizes or to evaluate their initial velocities. In addition, the tilted probes could be used to infer information on the global shape of the moving particle clouds.