The JILA instrument shops are a key factor in making JILA a unique research institution. It's been amazing to watch my fellow instrument makers flex their expertise. Making components of a clock that will be the nation's time standard is a big deal that has taken some real thought. In the fabrication stage, we're all regularly checking in with each other to make sure our parts fit and our designs agree. "It's incredibly rare to have a full shop collaboration like this," stated JILA instrument maker Adam Ellzey "All six of us sat in with Vladi during design consultations. To increase the cavity's Q, Gerginov collaborated with the machine and instrument shops at JILA, using the instrument shop and clean room to build the new microwave cavity out of copper. Keck Metrology Lab and Clean Room at JILA, "The quality of the cavity (Q) is very important to improve the clock's performance." According to Curtis Beimborn, Head of the W.M. To do this, the researchers leaned on the expertise found a JILA. "The frequency that a microwave cavity resonates at depends on the volume inside of it." "One of the crucial steps in building a cesium clock is tuning the frequency of the cavity to match the transition frequency of cesium," explained instrument maker Calvin Schwadron of JILA (a joint institute between NIST and the University of Colorado Boulder). "One of the issues was with the cavity's material (aluminum)."Īs atomic clocks are extremely sensitive to imperfections in the cavity shape, electrical conductivity, and polish, the cavity's materials have to be made of the right material, and have the exact shape, size and finish for minimizing clock inaccuracies. "We had issues with the previous clock cavity that limited the clock's accuracy," explained NIST scientist Vladislav "Vladi" Gerginov. The microwave cavity is a crucial piece of the timekeeping process, and researchers at NIST hoped to improve the accuracy of the clock by rebuilding the entire cavity. This definition is then applied to other clocks for calibration and accurate timekeeping. Once the microwave frequency is found, at which the microwave signal interacting with the cesium atoms would cause a maximum amount of them to change their state (at maximum fluorescence), that frequency is then used to define a second of time by counting exactly 9,192,631,770 signal periods (found by the scientists) with a counter. The entire process takes around one second, and is repeated multiple times to find the right frequency that excites the specific clock transition of the cesium atoms. 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. During the creation of this ball, the system is cooled to near absolute zero (zero Kelvin) to slow down the movement of the atoms.Īfter cooling, two vertical lasers toss the ball of cesium atoms into an upward arc (the "fountain") and then all laser beams are shut off. 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.
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