Publications

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The Velocity Interferometer System for Any Reflector (VISAR) is a widely used diagnostic at Sandia National Laboratories. Although the operating principles of the VISAR are well established, recently deployed systems (such as the fast push-pull and air delay VISAR) require more careful consideration, and many common assumptions about VISAR are coming into question. This report presents a comprehensive review of VISAR analysis to address these issues. Detailed treatment of several interferometer configurations is given to identify important aspects of the operation and characterization of VISAR systems. The calculation of velocity from interferometer measurements is also described. The goal is to derive the standard VISAR analysis relationships, indicate when these relationships are valid, and provide alternative methods when the standard analysis fails.

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Using shock wave reverberation experiments, water samples were quasi-isentropically compressed between silica and sapphire plates to peak pressures of 1-5 GPa on nanosecond time scales. Real time optical transmission measurements were used to examine changes in the compressed samples. Although the ice VII phase is thermodynamically favored above 2 GPa, the liquid state was initially preserved and subsequent freezing occurred over hundreds of nanoseconds only for the silica cells. Images detailing the formation and growth of the solid phase were obtained. These results provide unambiguous evidence of bulk water freezing on such short time scales.