Waves in two cavities placed along their path, and then selected by a magnetic gradient according to the resulting atomic state. Type, in which heated cesium atoms are emitted horizontally, exposed to electromagnetic ![]() Ramsey's method was first applied to cesium standards of the hot-beam, magnetic-selection The optically pumped cesium beam standard NICT-O1. By carefully maintaining the signal's phase between the two exposures, this revolutionary method delivers the same resolving power as if the atoms were constantly exposed during the interval between the two interactions. This problem was overcome with the development of Ramsey's method of separated oscillating fields, where the atom is only exposed to electromagnetic fields during two short periods. The cesium atoms can not be held in a fixed position during the measurement, which makes such extended measurements problematic. Narrow line widths typically require that the atom is exposed to the electromagnetic signal for an extended time. In other words, they need to observe the atomic spectrum with a very narrow line width. The performance of any atomic frequency standards depends on precisely determining the resonant frequency of the observed transition. History of primary frequency standard development at NICTĬesium fountain atomic spectrum recorded using Ramsey's method of separated oscillating fields. Primary frequency standard are therefore designed specifically to minimize and precisely control the residual effects, so that they can be quantitatively evaluated and corrected for. However, it is not possible to observe a signal under these conditions in a real experimental system. The cesium atom is expected to be at rest, in an environment of absolute zero temperature (0K), with no magnetic or electric fields, no gravitational effects and no interactions with other atoms or molecules. However, there a few assumptions that are not explicitly stated above. ![]() The International Bureau of Weights and MeasuresĪ primary frequency standard implements a frequency measurement according to this definition. It is defined by taking the fixed numerical value of the caesium frequency ΔνCs, the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be 9,192,631,770 when expressed in the unit Hz, which is equal to s –1. The second, symbol s, is the SI unit of time.
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