We have designed and used for several years now a ¼ inch O.D., 11.5 inch length optical probe for imaging light from a surface area inside a confined space. The design is based on a commercial SelFoc gradient index objective and relay rod combination with acceptance angle +-30 degrees. We have used our probe both for framing camera images and for imaging spots on a surface onto a fiber array for interferometry. Probe efficiency is 1x10-6 at an object distance of 10 centimeters, where, for imaging onto the array, the probe has a depth of field from 2 cm to infinity. If a spot size of 1 mm is acceptable, the object can be brought within a few mm. For interferometry, the probe images enough of the surface to require automation from the analysis software. Below we report our probe construction and performance calculations, and software automation and analysis improvements.

A new, non‐radiographic diagnostic has been developed that appears to provide information on multiple spall and damage layers in metals. The velocities of multiple layers (up to 5 in copper) can be determined using this method, with additional information possible on damaged material between layers at densities less than the bulk metal value. Metals that are melted on release (tin) also seem to exhibit a distinctive signature that is quite different from conventional multi‐layer spall. Experimental results on these metals and proton radiographs confirming these results are also presented.

Interferometric techniques have been used routinely for more than 20 years to measure velocities of explosive shock-fronts. Recently, structured-light measurements have been used for the same purpose. Explosions accelerate surfaces to as much as 15 km/sec in a nanosecond or less, often generating much light, large changes in reflectivity, and ejecting particles or layers at different speeds. I will describe the current performance of fiber-optic displacement-interferometers, Fabret-Perot inteferometers, velocity interferometers (VISAR), and structured light, in this interesting physical space. We have designed and used for several years a 1/4 inch OD optical probe with large depth of field that both illuminates and returns the image from a surface inside a confined geometry. We report on its design and performance. The increased information from the surface requires greater automation from the analysis software. We report our software automation and analysis improvements.

Multiple spall and damage layers can be created in metal when the free surface reflects a Taylor wave generated by high explosives. These phenomena have been explored in different thicknesses of several metals (tantalum, copper, 6061 T6-aluminum, and tin) using high-energy proton radiography. Multiple images (up to 21) can be produced of the dynamic evolution of damaged material on the microsecond time scale with a <50 ns "shutter" time. Movies and multiframe still images of areal and (Abel inverted) volume densities are presented. An example of material that is likely melted on release (tin) is also presented.

A Velocity Interferometer System for Any Reflector (VISAR) is a laboratory tool that measures high velocities by continuously measuring the Doppler shift of laser light reflected from a moving surface. It produces lower output frequencies than a displacement interferometer in which Doppler-shifted laser light from a moving target is mixed with unshifted laser light. To obtain lower frequencies a VISAR employs a wide-angle Michelson interferometer with a time delay in one leg. Undelayed and delayed light rays are thus mixed to detect the relatively small difference between two Doppler shifts produced by accelerating motion at two slightly different velocities. In most VISAR data reduction programs the velocity is assumed to be proportional to the interferometer fringe count at any instant. This yields velocity details that are inaccurate over the interferometer delay time. In the examples of this paper the signal time resolution was shorter than the interferometer delay. The subject of this paper is a data reduction method that uses the displacement information in suitable VISAR signals to recover velocity features that occur during the interferometer delay. 1.

A method for measuring the velocity history of a line element on a shock-loaded solid has been demonstrated. Light from a single-frequency laser is focused through a cylindrical lens to a line on a moving target. The return Doppler-shifted image is passed through a Fabry-Perot interferometer. Because only specific combinations of incident light angle and frequency can pass through the interferometer the output is an incomplete image of the moving target appearing as a set of fringes. This image is focused onto an electronic streak camera and swept in time. The fringe pattern changes with time as the target surface moves allowing determination of velocity for each point on the target that forms a fringe. Because the velocity can only be measured at the fringe positions it is necessary to use an interpolating polynomial to obtain a continuous function of time and velocity along the sampled line. 1.

Velocity interferomety has been used to determine velocities of miniature laser-driven flyer plates with sub-nanosecond (100 ps typical) time resolution. Since laser-driven flyer plates can have acceleration 101 0 m/s2 and attain 95 of terminal velocity within 20 nanoseconds the acceleration rate and terminal velocity cannot easily and accurately be resolved by current velocity interferometry techinques because of limitiations in temporal resolution of the interferometer and/or spatial resolution for conventional methods of recording raw data. By selecting an interferometer and recording system that is appropriate for the experiment sub-nanosecond time resolution is possible.

The VISAR (velocity interferometer system for any reflector) has become a common tool used in experiments where high surface velocities must be measured. A modification that uses previously wasted interferometer light to more than double output signals and to cancel noise is described. Laser power is used more efficiently, VISAR performance in the presence of intense target self-light is improved, and only two data signals are required instead of the usual three or four. Effects of changing light intensity and fringe visibility are eliminated using a novel detection system with a simplified solution for velocity.