Extending imaging VISARs into 3D with digital holography and phase retrieval

Velocity Interferometer Systems for Any Reflector (VISAR) systems can operate with fiber-coupled probes (non-imaging) or with spatially resolving image relays (imaging). Imaging VISARs can resolve the motion temporally in one spatial dimension (as in line-imaging VISAR on a streak camera) or spatially resolved in two dimensions and time gated (as in two-dimensional VISAR). Because the probe light is coherent it is possible to extend the imaging modality into the third spatial dimension using digital holographic techniques. A holographic recording provides both amplitude and phase of the reflected beam, which can then be propagated numerically and interrogated for detailed analysis. By combining a two-dimensional VISAR recording with a digital hologram we can resolve the velocity and spatial structure of reflecting systems throughout a three-dimensional volume down to the resolution limit of the imager. We list several possible applications of this capability: (1) simultaneous determination of both the amplitude (surface topography) and velocity (motion of the topographic structure) of a corrugated reflecting shock front; (2) a similar determination of the corrugation structure and motion of a reflecting perturbed interface between two media after passage of a shock (Richtmyer-Meshkov); and, (3) simultaneous measurement of the surface topography and velocity of the free-surface of a material upon release. In this talk, we will describe an extension to the two-dimensional VISAR diagnostic that provides the digital holographic capability and show initial benchtop experimental results. LLNL-ABS-832654