Lasers can give quartz glass properties of a metal for a few femtoseconds.
Everyone knows that glass – from window panes to laboratory test tubes to high-tech quartz glass – does not conduct electricity. But is it still true? Perhaps not.
Glass has always been used as an electrical insulator. But quartz glass can take on the properties of metals if an ultra-short laser pulse is applied to it for a number of femtoseconds. (One femtosecond equals one quadrillionth of a second, or one millionth of a billionth of a second.) This laser pulse has to be strong enough to make electrons in the glass material move around quite freely.
During this period, the usually clear glass will become opaque and will be able to conduct electricity just like a metal. This is such an ultra-fast phenomenon that it may be applied in future to create ultra-fast electronics.
Once the laser pulse is removed, the glass reverts to its original state. This strange effect has been studied by scientists at the Vienna-based University of Technology in Austria. They explain the effect as similar to one where a ball bounces around on an uneven surface. If the ball has only a small amount of energy, it will come to rest quickly in a dent on the surface. But if the ball is given a high amount of energy, it can move freely around the surface without becoming stuck.
So when the laser pulse is applied to the quartz glass, quantum mechanics will come into play. Electrons that are attached to a single atom within the material become energised by the powerful electrical field created by the laser pulse. This energy injection from the laser pulse not only allows the electron to jump to a higher energy level in the material, but it also distorts all of the states of electrons throughout it.
As a result, an electron that previously was attached to an oxygen atom (glass is the chemical compound silicon dioxide) can jump to a silicon atom or another oxygen atom and then move around the entire material quite freely. This is the behaviour of electrons in a metal when subjected to an electrical field. Such movement gives the metal, or the material, the properties of an electrical conductor.
However, such charges in ordinary transistors move at speeds of picoseconds, or trillionths of a second. The effect in quartz glass makes this process one thousand time faster.
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