NOW there鈥檚 no excuse for being more than a million-billionth of a second
late. Researchers at the US government鈥檚 National Institute of Standards and
Technology in Boulder, Colorado, have created a 鈥渇emtosecond鈥� clock so accurate
that it would be no more than a second out after 30 billion years.
The clock counts the oscillations of a laser beam, which are held at an exact
frequency by linking the laser to electrons jumping between energy levels in a
mercury ion. These transitions tune the laser oscillator to 鈥渢ick鈥� 100,000 times
as fast as conventional atomic clocks, which are based on caesium atoms. The
faster tick improves timekeeping.
The researchers, whose invention will be described in a future issue of
Science, expect it to improve navigation by satellite, which relies on
accurate time measurements.
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