ALEXANDER TSIARAS / SCIENCE PHOTO LIBRARY ALEXANDER TSIARAS / SCIENCE PHOTO LIBRARY
James Berquist of the US National Institute of Standards and Technology (NIST) studying a dye laser used in the NIST-7 atomic clock. The dye laser is one of many lasers used in this clock. The job of the dye laser is to excite hydrogen ions contained in an ion trap. Once raised to a higher energy state by the laser, the ions start to oscillate between energy levels. Other lasers are used to count these oscillations, providing the basis for extremely accurate time keeping. When operational in 1992, NIST-7 wil be the world's most accurate atomic clock, with a precision of one billionth of a second per day (one second in three million years).
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