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Ultrafast Laser Frees Prehistoric Fossils

Photonics Spectra
Jan 2000
Michael D. Wheeler

LIVERMORE, Calif. -- A technique based on a scanning, ultrafast laser could soon prove invaluable to paleontologists attempting to liberate fossils entombed in surrounding rock.

Physicists from Lawrence Livermore National Laboratory, working on their own time, have refined a system that monitors the composition of the target and cuts power to the laser when it detects fossilized bone. The result could be a dramatic improvement over the current mechanical cleaning method used by paleontologists, which is both delicate and painstaking. It often takes months to prepare small fossils and years for entire dinosaurs.

The new method involves the use of a powerful, ultrafast laser emitting at 800 nm that is capable of producing a train of 1000 1-mJ pulses per second. "The laser system being used is a homegrown one -- a 'kid brother' of the petawatt laser system first developed at Lawrence Livermore as part of the National Ignition Facility [program]," said Lowell Wood of Livermore.

Because the pulses are so short, the top layer of the target absorbs nearly all the energy, leaving those below unscathed. This permits the automated, raster-type scanning of a large surface to remove one 1-µm layer after another as deep as may be desired.

Emission spectrum

The system determines the composition of the material by analyzing the emission spectrum of the vapor plume. To do this the researchers use optical spectrographic monitoring to observe the ablated material on the fly as well as to map the object in either two or three dimensions.

The laser switches off as soon as it detects phosphorus -- an element rare in ordinary rock but a primary component of fossilized bone. This sensitivity enables the user to preserve the fossil's surface structure to a degree previously impossible.

The team, which also includes Brent Stuart and Muriel Ishikawa of Lawrence Livermore, hopes to present several fossils prepared with the technique at next year's annual meeting of the international Society of Vertebrate Paleontology. Wood predicts that the method, with its high-speed and high-resolution pixel-by-pixel composition analyses, could find extensive commercial applications in the next 10 years, although specifics of other mainline applications are not publicly available.


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