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Record-breaking laser is hot stuff

May 12, 2006 By Mark Peplow This article courtesy of Nature News.

The record for the fastest rise in temperature has just been topped.

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With the heat of a burning sun, a laser pulse has ripped through pure sapphire, heating it faster than any explosion ever recorded.

The experiment was a blast, say physicists who reckon their laser can drive temperature increases of a billion billion (1018) degrees per second, although they could only keep it going for a couple of hundred femtoseconds (with a femtosecond being 10-15 s). That tops the previous heating-rate record, they say.

The intense heating power of the laser made miniature fireballs, just thousandths of a millimetre in size, at pressures of 10 terapascals (1013 Pa). That's about 20 times the pressure at the Earth's core. Although more powerful lasers have previously managed to create greater pressures, these required large, specialized facilities.

The intense crush also raised the temperature to about half a million °C. "You have the same parameters in an atomic explosion," says Vladimir Tikhonchuk, a theoretical physicist from the University of Bordeaux, France.

The success shows that scientists can now simulate the intense condition at the hearts of planets, or possibly even trigger fusion reactions, using a conventional tabletop laser.

High-pressure job

Tikhonchuk says similar heating rates have probably been generated before in experiments that used laser light to drill holes through materials. But no one had actually worked out the temperatures and pressures involved in those cases, he says, and this probably tops them. "We have also focused the pulse to a much smaller size," he adds. "Because of that we have a very high energy delivery."

The laser shots themselves were overseen by Saulius Juodkazis, at Hokkaido University, Japan, while Tikhonchuk helped to calculate the intense conditions based on the size and shape of the tiny teardrop cavities left behind in the sapphire by the explosive bursts of energy.

Each laser pulse lasted just 200 femtoseconds, enough time for light travelling in a vacuum to zip across the width of a human hair. The sapphire exploded under the heat in just a few femtoseconds, and as the ball of shredded atoms grew it became much less dense, making further heating much less efficient. "The trick is to heat the plasma before it starts to expand," says Tikhonchuk.

To put the pressure in perspective, 10 terapascals (1013 Pa) would be generated by two Great Pyramids of Giza balancing on a CD, or a couple of hundred elephants dancing on the head of a pin.

Although the temperature rise is thought to be the fastest observed yet, it's a long way from reaching the highest temperature recorded on Earth. That prize goes to the Z machine at Sandia National Laboratories, Albuquerque, New Mexico, which sends millions of amps of electricity coursing through fine tungsten wires to create conditions for atomic fusion. Earlier this year, Sandia scientists reported that their experiment had topped 2 billion °C2.

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  1. Juodkazis S., et al. Phys. Rev. Lett. , 96, 166101 (2006).
  2. Haines M. G., et al. hys. Rev. Lett., 96, 075003 (2006).


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