Deriving Particle Distributions from In-Line Fraunhofer Holographic Data

Holographic data are acquired during hydrodynamic experiments at the Pegasus Pulsed Power Facility at the Los Alamos National Laboratory. These experiments produce a fine spray of fast-moving particles. Snapshots of the spray are captured using in-line Fraunhofer holographic techniques. Roughly one cubic centimeter is recorded by the hologram. Minimum detectable particle size in the data extends down to 2 microns. In a holography reconstruction system, a laser illuminates the hologram as it rests in a three-axis actuator, recreating the snapshot of the experiment. A computer guides the actuators through an orderly sequence programmed by the user. At selected intervals, slices of this volume are captured and digitized with a CCD camera. Intermittent on-line processing of the image data and computer control of the camera functions optimizes statistics of the acquired image data for off-line processing. Tens of thousands of individual data frames (30 to 40 gigabytes of data) are required to recreate a digital representation of the snapshot. Throughput of the reduction system is 550 megabytes per hour (MB/hr). Objects and associated features from the data are subsequently extracted during off-line processing. Discrimination and correlation tests reject noise, eliminate multiple counting of particles, and build an error model to estimate performance. Objects surviving these tests are classified as particles. The particle distributions are derived from the data base formed by these particles, their locations and features. Throughput of the off-line processing exceeds 500 MB/hr. This paper describes the reduction system, outlines the off-line processing procedure, summarizes the discrimination and correlation tests, and reports numerical results for a sample data set