This locked frequency is then divided by 9,192,631,770 to give the familiar one pulse per second required by the real world. This peak is then used to make the slight correction necessary to bring the crystal oscillator and hence the microwave field exactly on frequency. A detector at the end of the tube gives an output proportional to the number of cesium atoms striking it, and therefore peaks in output when the microwave frequency is exactly correct. When a cesium atom receives microwave energy at exactly the right frequency, it changes its energy state.Īt the far end of the tube, another magnetic field separates out the atoms that have changed their energy state if the microwave field was at exactly the correct frequency. The range of the microwave generator is already close to this exact frequency, as it comes from an accurate crystal oscillator. The frequency of the microwave energy sweeps backward and forward within a narrow range of frequencies, so that at some point in each cycle it crosses the frequency of exactly 9,192,631,770 Hertz (Hz, or cycles per second). First they pass through a magnetic field that selects atoms of the right energy state then they pass through an intense microwave field. First they pass through a magnetic field that. Please contact us to discuss your requirements.To create a clock, cesium is first heated so that atoms boil off and pass down a tube maintained at a high vacuum. To create a clock, cesium is first heated so that atoms boil off and pass down a tube maintained at a high vacuum. Atomic clocks are designed to measure the precise length of a second, the base unit of modern timekeeping. 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. In this clock, atoms of vapourised caesium-133 oscillate between two energy levels as they pass back and forth between magnets at each. 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. Fibre optic links eliminate GNSS jamming, spoofing, urban canyon effects and solar storms to ensure resilience and security. It is therefore directly traceable and certified to UTC at the point of provision. 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. NPL Time® is monitored and maintained 24/7 up to the point of entry to your network. ![]() 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. The first caesium clock was built by Louis Essen in 1955 at the National Physical Laboratory in the UK. The apparatus for this measurement is named NBS-1. The caesium standard is a primary frequency standard in which the photon absorption by transitions between the two hyperfine ground states of caesium-133 atoms is used to control the output frequency. World-class frequency standards that you can rely on 1952 - NIST completes the first accurate measurement of the frequency of the cesium clock resonance.
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