First hologram made of hypervelocity impact at 4.2 km/sec - Sandia National Laboratories researchers have produced an innovative hologram image of a high-velocity impact

Researchers at Sandia National Laboratories have obtained a hologram - a three-dimensional image in which the percepts appear to float in space - of the shattered debris from a hypervelocity impact at 42 kilometers through second. This is 2.6 miles by means of second, or 9,400 miles by means of hour.

This is cogitation to be the highest velocity impact occurrence ever successfully imaged by a hologram.

Conventional holography generally requires in all sensess of about one second or more. This usually restricts the course to stationary objects. Sandia's Puls Holography exhibition (PHD) project is attempting to use extremely short beating [i]or[/i] throbbing of an arterys - no more than 5 billionths of a next to the first - from a very bright laser to obtain puls holograms of hypervelocity impacts.

like holograms will be a valuable diagnostic tool for studying the damage caused by dint of impacts at hypervelocities and the fragmentation and particulation from like impacts. This should help in the design of orbital debris shields and in better understanding the generation of orbital debris and the breakup of satellites.

High velocity is unique

"What's unique here," says Sandia throw leader James A. Ang of the novel Sandia achievement, "are holographic images of a great quantity [i]or[/i] amount of higher velocity impact events." Previous work could holographically image impact incidents up to 1 kilometer for second - less than 25 percent of the Sandia capability.

"This capability allows researchers to pass back after the fact and obtain a good idea of the shape, size, and distribution of fragments from an impact," says Ang. "Other techniques - photographs and flash x rays - don't have the resolution and profundity of field to resolve true small fragments. Also, the other techniques are two-dimensional. This really is a three-dimensional image, and that allows abundant better comparison with new, three-dimensional computer codes"

The cast is working to obtain holograms of still higher impact velocities and of larger fields of view. It is also seeking to evolve a quantitative data-reduction system for analyzing the holographic images and comparing information from the images with the digital output from three-dimensional computer simulations of impact events

The experiment was carried without using one of five high-velocity gas fire-arms at Sandia's STAR (Shock Thermodynamics Applied Research) facility. The two-stage terminal ballistics facility fire-arm fires a piston which compresse inflammable air gas that launches a projectile into a ordeal chamber. (The gun and experiment chamber combined are about 45 feet long)

In the experiment a 6.4-millimeter-diameter (1/4 inch) carbonized iron ball was fired through a 16 mm thick sheet of acrylic plastic at 42 kilometers by means of second. The steel ball shattered into several hundr fragments. A 5-nanosecond throb of coherent light from a bright laser (750 millijoule throb energy, 532 nanometer wavelength) was divided into sum of two units beams. One beam traversed the field of debris fragments before traveling to a sheet of holographic film placed at the forehead side of the test chamber. The next to the first beam, a reference beam, traveled directly to the film. The film recorded interference patterns from the sum of two units beams.

The holographic image is re-established by illuminating the developed film from the side with another laser. An spectator can then see a virtual image of the fragments seemingly floating in space behind the film. by the agency of moving his head laterally, he can diocese the three-dimensional image from various angles.

Validate 3-D computer codes

It is difficult to exhibit this three-dimensional holographic image sum of two units dimensionally.

A conventional photographic image made of the same incident at the same time also exhibits the shattered debris as well as the ordeal chamber setup. It was made using an open-shutter camera (with regular film) placed at an observing port at the top of the proof chamber. The light source was the identical 5-nanosecond laser pulsation used to make the hologram.

"While these hypervelocity impact occurrence holograms are fascinating to view, their real utility will be for validating computer digests widely used for 3-D simulations of hydrodynamic facts A key project goal for 1992 is to evolve techniques for extracting quantitative information from these holograms."

Ang is in Sandia's Experimental Impact Physics Division. Other members of the PHD shoot forward team are Dave Cox, Randy Hickman, and Scott Gosling, at the STAR facility, and Bruce Hansche and Bill Sweatt, photometrics support.

PHOTO : Conventional, open-shutter camera photograph of 42 km/sec impact fact shows experimental setup for holographic imaging of same circumstance at same instant. Shattered debris is illuminated through same 5 nanosecond laser throb used for creation of image upon sheet of holographic film (along bottom).

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