Development of an all fiber velocity interferometer dedicated to measurement of thermal stress waves on samples irradiated by Sphinx Z-pinch source

Summary form only given. An all fiber 1550 nm heterodyne velocimeter (HetV) has been developed at CEA Gramat to measure thermal stress waves on samples irradiated by Sphinx Z-pinch source. Previously, wave´s velocities were measured by VISAR, for which the setup and adjustement procedures were heavy compared to those of the all fiber HetV. For both diagnostics, the low velocity and fast rise time of the mechanical strain are the main issues in terms of unfolding techniques. In VISAR measurements, the time resolution is inversely proportional to the velocity per fringe (VPF) chosen. Hence, in order to achieve good temporal resolution for a fast rise time signal, on needs to increase the VPF, which is not optimal at relatively low velocities. In HetV measurements, velocity can be inferred from the signal beat frequency, but the typical mechanical strain dynamics results in less than a fringe shift during the pulse rise time; hence signal processing by a short-time Fourrier transform is ineffective. Therefore HetV has to be considered as a displacement interferometer, where a complete fringe shift is equivalent to a displacement of lambda/2 of the moving surface. Simultaneous VISAR and HetV measurements were carried out on irradiated samples. The results obtained using both interferometric techniques are quite consistent.