Largest Laser Shocks Diamond into Metal
Laurel M. Sheppard
LIVERMORE, Calif. -- Though physicists may be jumping for joy, those who consider diamonds their best friends won't be. Scientists at Lawrence Livermore National Laboratory have turned diamond into metal.
Using the Nova laser, whose 10 beams can produce more than 30 TW, Gilbert Collins and colleagues relied on a shock compression method to perform this feat. In this method, large amounts of energy are added suddenly to a material system, creating intense sound or pressure waves that become shock waves. Shock waves then compress the material to greater pressure (millions of atmospheres), changing it to a state of higher density and temperature.
The scientists previously used this method to convert the hydrogen isotope deuterium from a gas into a metal. The data from these experiments provided a revised equation of state for hydrogen, which is important for high-energy-density physics applications. The new equation of state will also change the way planets such as Jupiter are modeled, especially the size of its metallic core.
In the more recent experiment, an aluminum target, to which a small diamond is attached, is used to absorb the laser energy and to transmit the shock wave into the diamond. Three laser beams are used: one Nova beam to shock the diamond, a second Nova beam to create an x-ray source for transverse radiography to obtain shock-wave and reflectivity measurements, and the third beam from a tabletop laser for optical interferometric measurements. The latter is used to determine the shock speed, which helps determine the pressure at which a change in reflectivity occurs. A higher reflectivity (around 60 percent) is characteristic of a reflecting metal.
After shocking the diamond, the surface begins reflecting light like a metal. The scientists believe that the transition occurs when the diamond melts, opening up the structure so electrons can move freely.
This metallized form of diamond may be similar to the matter at the core of dense stars, such as white dwarfs, which form when they lose their thermal energy. Studying the characteristics of melted diamond could help astronomers understand what is happening inside the fading stars.
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