Free-surface velocity measurements of opaque materials in laser-driven shock-wave experiments using photonic Doppler velocimetry

We present a novel photonic Doppler velocimetry(PDV)design for laser-driven shock-wave experiments.This PDV design is intended to provide the capability of measuring the free-surface velocity of shocked opaque materials in the terapascal range.We present measurements of the free-surface velocity of gold for as long as∼2 ns from the shock breakout,at pressures of up to∼7 Mbar and a free-surface velocity of 7.3 km/s with an error of∼1.5%.Such laboratory pressure conditions are achieved predominantly at high-intensity laser facilities where the only velocity diagnostic is usually line-imaging velocity interferometry for any reflector.However,that diagnostic is limited by the lower dynamic range of the streak camera(at a temporal resolution relevant to laser shock experiments)to measure the free-surface velocity of opaque materials up to pressures of only∼1 Mbar.We expect the proposed PDV design to allow the free-surface velocity of opaque materials to be measured at much higher pressures.