Vanadium Dioxide is Fast

Timing nature’s fastest optical shutter

It's nature's fastest quick-change artist: In less than the time it takes a beam of light to travel a tenth of a millimeter, vanadium dioxide can switch from a transparent to a reflective, mirror-like state.
How this material (VO2) can turn from a transparent insulator into a reflective metal so rapidly has physicists scratching their heads, but a collaboration among researchers at Vanderbilt, Oak Ridge National Laboratory and Lawrence Berkeley National Laboratory has clocked the transfiguration at one-tenth of a trillionth of a second.