A laser velocity interferometer instrumentation system has been developed which can measure the velocity history of either spectrally or diffusely reflecting surfaces. The system provides two interferometer fringe signals in quadrature to improve resolution and to distinguish between acceleration and deceleration. Accuracies of 2% or better are attainable for peak surface velocities of 0.2 mm/μsec or more. The system has been applied to the measurement of free surface motion in plate-impact experiments, and to the measurement of the velocity history of a projectile during its acceleration down a long gun barrel.

The shock-wave propagation characteristics of polymethyl methacrylate (PMMA), fused silica, and sapphire were measured for both compressive and rarefaction waves using plate-impact experiments and interferometer instrumentation techniques. The peak stress levels in the experiments were 22, 65, and 120 kbar, respectively. The high-resolution measurements of the stress wave profiles showed the PMMA to be a complex material whose wave propagation is influenced by nonlinearity, strain-rate dependence, and elastic-plastic effects in which plastic working increases the zero-pressure volume of the material. The fused silica is very well characterized as a nonlinear elastic material having the interesting property of propagating stable rarefaction shock waves. The sapphire was nearly linear elastic to 120 kbar. The use of these three transparent materials as ``windows'' in laser interferometer instrumented shock-wave studies of other materials is discussed. The effect of the shock-induced variation of the index of refraction on the interferometer data was also measured and is presented.

Plate impact experiments producing plane waves of up to 40 GPa (400 kbar) peak stress were performed using Armco iron specimens and impactors. Highly accurate time-resolved measurements of the resulting free-surface velocities of the specimens were obtained with the VISAR laser interferometer instrumentation system. The free-surface velocity profiles provide new information concerning the rate effects associated with the α → ε polymorphic phase transition at 13 GPa, the material strength and release wave speeds at 10 and 40 GPa, and the stress level at which the iron reverts back to the α phase on unloading. A strong magnetic field was found to produce no measurable change in the phase-transition stress. The accuracy of the ``factor-of-2'' assumption relating free-surface velocity to particle velocity in iron was also evaluated experimentally.

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A Doppler shift in wavelength can result in a very slight change in the index of refraction of a transparent material due to disperison. This effect, if not accounted for, produces an error of a few percent in the velocities determined using the recently developed velocity interferometer for diffusely reflecting surfaces.