Caesium clock11/7/2023 Large hyperfine transition, creating better Q of the resulting resonator.Īs opposed to rubidium, cesium only has one stable isotope, so getting a really pure gas is much easier. In part this is because it was chosen as the standard, and as such it is considered more useful to spend development effort on improvements to the standard rather than an alternative.īut why was cesium chosen? Various factors:Īt reasonable temperatures, cesium has a high vapor pressure, making resonance effects relatively easy to observe. But the best performance comes from using cesium. At the very least, rubidium and hydrogen clocks are common, and you can get rubidium standards on eBay for well under $200. It's worth noting that your statement "Modern atomic clocks only use caesium atoms" is simply untrue. The choice of cesium is due to various factors. Which made it the preferred element then the standard and now, pretty much the only one used. When you put all the possible candidate elements against this table, you find that Cs-133 is your top candidate. a high frequency for the transition (more accurate measurement in shorter time).an atom with just one stable isotope (so you don't have to purify it, and don't get multiple lines).an atom with a magnetic field (for the electron - field interaction): odd number of protons/neutrons.an atom that can easily be vaporized at a low temperature (in solids, Pauli exclusion principle causes line broadening in hot gases, Doppler broadening comes into play).To answer that we have to look at the principle of an atomic clock: you look at the frequency of the hyperfine transition - a splitting of energy levels caused by the magnetic field of the nucleus. Please contact us to discuss your requirements."Because that is how the second is defined" is nice - but that immediately leads us to the question "why did Cesium become the standard"? The long-term accuracy of this fountain standard is at parts in 10 16, limited by uncertainty of systematic frequency shifts, such as perturbations by stray external fields.ĭon’t see what you are looking for? Our diverse skill set enables us to provide bespoke solutions. This enables frequency measurement precision equivalent to less than 1 part in 10 13 for one second of averaging time. Using atoms, which are slowed down by laser light (laser cooling technique) and fly freely under gravity (as in a fountain), greatly increases the interaction time with the microwaves. A small change in the measured probability is a direct measure of the frequency deviation of the local oscillator, which can be corrected accordingly, and the value is recorded for analysis. A microwave signal from a local oscillator is tuned to the ground state hyperfine transition of the Cs atoms and the probability of the transition is measured. It comprises a physics package, lasers and optics for cooling and probing, as well as control electronics. The design of our commercial caesium (Cs) fountain is based on those we operate at NPL, which contribute to the international time scale, UTC, and provide stability for the UK national timescale, UTC(NPL). Our cost-effective solutions can be used to increase the availability of accurate frequency references and timescales in critical locations. The standard will also be useful to observatories which require precise timing for astronomical observations and satellite laser ranging.Ĭustomers can trust our proven ability to deliver complex measurement systems to organisations, including other national measurement laboratories. The long-term stability, better than 100 ps/day, and accuracy of the standard can be used to correct clocks which form local time scales in national timing laboratories or in academic and industrial institutions. We can supply caesium fountain primary frequency standards to other national standards laboratories or organisations needing direct reference to a realisation of the SI second, such as time distribution centres and large scientific facilities. The caesium fountain primary frequency standard apparatus is used to realise the SI definition of the second and contributes to the construction of the international time scale, UTC. World-class frequency standards that you can rely on
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