Photonic Doppler Velocimetry (PDV) systems are developed to measure velocities in physics experiments such as ramp compression experiment on novel materials. Better time resolution, in the fast acceleration phase, is required when the velocity reached is limited to few tens of m/s. This resolution being proportional to the wavelength, a green PDV system provides a factor 3 gain compared to a telecom based PDV. Furthermore, a Triature design allows to further increase the time resolution thanks to the phases signal processing. A 532-nm Triature PDV system was realized with singlemode fibers (4.5 µm core diameter) and compared to three standard PDV systems in reproducible ramp compression experiments. To minimize the optical losses, most of the fibers components were fused. The velocity profile measured has oscillations between 0 and 10 m/s. The first velocity peak is reached in 1.0 µs. The 1550-nm homodyne PDV system provides only 6 fringes and it clearly limits the time resolution. The 1550-nm heterodyne PDV system provides hundreds of fringes but variations of about 0.1 m/s are observed. The green homodyne PDV system provides almost the correct velocity profile by Short Time Fourier Transform. The 250-ns long acceleration phase is better resolved applying a signal processing with at least two phases.
A method for obtaining time-resolved diffraction data from laser-shocked solids was developed at the High-Energy beamline ID15 of the European Synchrotron Radiation Facility. This method combines the use of an appropriate timing electronics with a triple-axis diffractometer coupled to a short-pulsed laser source. Real time diffraction measurements were performed on single crystalline samples in order to monitor their compression under different loading conditions through the evolution of the Bragg reflection. As an example, we present results obtained from cadmium sulfide single crystals at stress values below and near the Hexagonal-Closed Packed to Rock Salt pressure-induced phase transition. These results clearly show two different behavior when the sample is compressed below and above its elastic limit.
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