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Phone: 613-993-2181
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Generation of the SI unit of time and frequency
Cesium clocks use the natural oscillation frequency of cesium atoms, which is exactly 9192631770Hz by definition. Using an electronic circuit to count 9192631770 oscillations, the cesium fountain clock exploits the principle that if you measure a frequency over a longer period of time, you will obtain a better measurement. In the fountain clock, the cesium atoms are slowed down with lasers and launched upwards to a height of one meter. the trajectories of these atoms form the shape of a water fountain, which inspired the name for this type of clock. The time it takes for the atoms to go up and return is about half a second, 100 times longer than a traditional clock. The frequency measurement is therefore 100 times more precise so that a very good clock can be built based on this principle. By averaging many measurements over periods of hours, a very stable time scale is produced.
Dr. Rob Douglas, Research Officer in the Frequency and Time group, makes adjustments to one of the NRC-built cesium atomic clocks. The large aluminum tube is a vacuum vessel which contains the heart of the clock. Cesium atoms are emitted at one end of the tube and pass through two microwave cavities (the copper waveguide which feeds the microwaves to these cavities can be seen above the tube) before they are analyzed and detected at the other end. The control electronics are shown in the lower part of the photograph.
