Optical technique for determining rarefaction wave velocities at very high pressures

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Abstract
An optical technique to determine rarefaction wave velocities is described. The technique utilizes the property that many transparent materials emit copious radiation when shocked to high pressures. The usual method of producing a rarefaction wave by impacting a target plate with a thinner rapidly moving driver plate is employed. The target plate is made in the form of a step wedge which is covered by the transparent material (or analyzer). When the shock reaches the analyzer it radiates steadily until the rarefaction from the backside of the driver plate overtakes the shock front causing the radiation to decrease. The time between these events is a decreasing linear function of the target thickness and when extrapolated to zero determines the thickness where the rarefaction would have overtaken the shock wave at the surface of the target. Light pipes are used to transmit the radiation to photomultipliers whose response is measured by high‐speed oscilloscopes.