New Atomic Clock Uses Femtosecond Laser

DENVER, Colo., Feb. 19 -- A new all-optical atomic clock is so accurate, its creators theorize it won't lose or gain a second in 4.5 billion years.

Using a femtosecond laser to measure time intervals too tiny to be measured in nanoseconds, Scott A. Diddams, a researcher with the National Institute of Standards and Technology in Boulder, and his colleagues said they were able to keep time with greater precision than with existing atomic clocks -- by five orders of magnitude. They discussed improvements in the femtosecond laser technology, and their efforts to make counters for the new optical clocks, at the American Association for the Advancement of Science (AAAS) annual meeting here last week.

The optical clock was made possible by technological advances in measuring optical frequencies and in capturing and cooling single ions to very low temperatures, the researchers said. It uses nonlinear optical fibers to generate optical-frequency "combs," which are used to determine frequencies by counting the number of "teeth" in the comb.

Diddams and his colleagues developed the optical clock based on a single trapped mercury ion, and they said their research may someday end the reign of microwave atomic clocks, which use cesium 133 atoms to determine the time. Cesium atoms resonate exactly 9,192,631,770 times per second when irradiated by a magnetic microwave field. So clocks that adhere to that frequency are extremely accurate, Diddams said. The cesium clock is thought to be able to maintain the correct time for 20 million years -- a mere blink of an eye, however, when compared to the 4.5 billion years of accuracy claimed for the optical timekeeper.

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