Optically Recording Velocity Interferometer System Research Articles

Optically recording velocity interferometer system configurations and impact of target surface reflectance properties [invited

The utility of the optically recording velocity interferometer system (ORVIS) diagnostic to be configured to meet specific experimental needs in terms of line- and surface-imaging modes enabling direct control of the spatial, temporal, and velocity sensitivities is presented along with two case studies of gas gun testing with highly heterogeneous materials. These experiments have successfully coupled two and three ORVIS interferometers onto a single experiment. Light collection from the target reflector is of critical importance to successful test execution. By utilizing the established field of electromagnetic wave scattering from rough surfaces, the reflectance characteristics of several ORVIS reflectors are qualitatively and quantitatively analyzed in terms of the surface roughness statistics, power spectral density, and bidirectional reflectance distribution function. Insights into the impact of the surfaces on ORVIS image records are quantified. Through method development for quantitatively characterizing reflector surfaces, future experimentation can begin with an ability to tailor a reflector to a given test material and experimental arrangement.

Measuring three-dimensional deformation with surface-imaging ORVIS

With growing interest in understanding heterogeneous material phenomena under shock compression and the advancement of computational methods, three-dimensional data suitable for model validation and scientific pursuit is needed. The optically-recording velocity interferometer system (ORVIS) is a velocity interferometer that measures the apparent motion of a set of parallel interference fringes. Initially demonstrated for collecting one-dimensional data at a point using a streak camera and a focused laser spot, line-imaging ORVIS is a useful extension for the collection of two-dimensional data using a streak camera and a laser light sheet. We extend ORVIS operation further to a surface-imaging mode for collecting three-dimensional data using a framing camera and an expanded region of laser illumination. In surface-imaging mode, snapshots of surface velocity across a cross-sectional area are collected at regular time intervals and combined to yield the surface velocity history. Surface-imaging ORVIS is demonstrated through an analytical model of a vibrating circular membrane and an experimental and analytical model of a rotating ellipse. A discussion of the analysis methodology and some experimental challenges are discussed.

ADL ORVIS: an air-delay-leg, line-imaging optically recording velocity interferometer system.

An interferometry system that enables acquisition of spatially resolved velocity-time profiles with very high velocity sensitivity has been designed and applied to two diverse, instructive experimental problems: (1) measurement of low-amplitude reverberations in laser-driven flyer plates and (2) measurement of ramp-wave profiles in symmetric impact studies of fused silica. The delay leg in this version of a line-imaging optically recording velocity interferometer system (ORVIS) consists of a long air path that includes relay optics to transmit the optical signal through the interferometer cavity. Target image quality from the delay path at the image recombination plane is preserved by means of a compact and flexible optical design utilizing two parabolic reflectors (serving as the relay optics) in a folded path. With an instrument tuned to a velocity per fringe constant of 22.4 m s(-1) fringe(-1), differences of 1-2 m s(-1) across the probe line segment can be readily distinguished. Measurements that capture small spatial variations in flyer velocity are presented and briefly discussed. In the fused silica impact experiments, the ramp-wave profile observed by this air-delay instrument compares favorably to the profile recorded simultaneously by a conventional line-imaging ORVIS.

Development of laser-driven shock compression system with a line-imaging ORVIS to determine the Hugoniot equation-of-state

A laser-driven shock compression system using a table-top type pulsed laser was developed in order to investigate the Hugoniot equation-of-state (EOS) of laser-shocked materials. A line-imaging optically recording velocity interferometer system (ORVIS) was implemented for measurements of both shock wave velocity (Us) and particle velocity (up). The measurement of Hugoniot equation-of-state of nitromethane was performed by using the developed experimental system. The obtained experimental results showed a good agreement with the previous data. It was indicated that the developed experimental system and the analytical method implemented in this study were worked well and useful to investigate the Hugoniot equation-of-state of transparent materials such as nitromethane.

Hydrogen effects on the spall strength and fracture characteristics of amorphous Fe-Si-B alloy at very high strain rates

A novel approach is suggested, using laser-induced shock wave measurements to estimate the effects of cathodic hydrogen charging on the mechanical properties and fracture characteristics of materials. This approach is applied to (1) determine the dominant mechanism of hydrogen embrittlement (HE) in an amorphous Fe80B11Si9 alloy; and (2) estimate the effects of the high pressures involved in cathodic charging. The dynamic spall strength of an amorphous Fe80B11Si9 alloy shocked before and after hydrogenation by a high-power laser to very high pressures (tens of giga Pascals) is measured. The dynamic spall strength of crystalline iron is measured as well for comparison. An optically recording velocity interferometer system (ORVIS) is used to measure the profile of the free surface velocity in time. The spall strength and the strain rate are calculated from the measurement of the free surface velocity as a function of time. Fracture characteristics are studied by scanning electron microscopy (SEM). The main conclusions are (1) the most reasonable mechanism of HE in the amorphous Fe-Si-B alloy is the high-pressure bubble formation; (2) the high pressures involved in cathodic hydrogen charging or laser-induced shock waves measurements may have similar effects on fracture characteristics; and (3) at very high strain rates, the spall strength is determined mainly by the interatomic bonds.