![]() ![]() The final atomic state is determined by measuring the fluorescence of the altered atoms induced by another laser beam. The ball then drops, and again, the microwave field may interact with the atoms, causing more of them to change their state. The cesium ball moves upwards for about a meter in a special microwave-filled cavity, which may alter some of the atoms within the ball. After cooling, two vertical lasers toss the ball of cesium atoms into an upward arc (the “fountain”) and then all laser beams are shut off. During the creation of this ball, the system is cooled to near absolute zero (zero Kelvin) to slow down the movement of the atoms. These cesium atoms begin in a special vacuum chamber, where six infrared laser beams herd the free-flying atoms into a ball. The NIST-F1 clock is also called a “fountain clock” due to the fountain-like movement of the cesium atoms inside the clock that is used to measure time intervals. For the NIST-F1 cesium clock specifically, this process has included rebuilding parts of the clock. The National Institute of Standards and Technology (NIST) laboratories in Boulder, Colorado have housed atomic clocks-including the cesium atomic clock NIST-F1 which serves as the United States' primary time and frequency standard-for decades, as researchers continue to improve the clocks' accuracies through cutting-edge research. The cesium atomic clocks play a consequential role, as a specific atomic transition induced in the atomic cesium is used to define the unit of time: the SI second. They are some of the most accurate clocks in the world and the most fragile. Some of these clocks use lasers and special resonator cavities to measure time intervals. Atomic clocks are crucial for everyday living as they help our telecommunications, electrical power grids, GPS systems, transportation, and other processes around the world keep precise time. ![]()
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