Resources for Time & Frequency Metrology

With the advent of atomic frequency standards (atomic clocks), it has become possible to measure frequencies with extremely high precision and accuracy. The definition of frequency has been referenced to a microwave transition of the cesium atom, and it is routinely measured to a few parts in 10-16 by individual laboratories. On shorter scales, frequency standards under development are already capable of measuring frequencies to precisions of 10-18 and even below. For these reasons frequency measurements may well be the most precise and accurate types of measurements ever made by humankind. Time, as the integral of the frequency, is operationally measured at the level of nanoseconds over long distances, and at the several picosecond level within laboratories.

The construction of atomic clocks is an experimental art drawing heavily on quantum mechanics, relativity, and statistics. Conversely, data from atomic clocks has provided important tests of physical theories, and inspired the development of new mathematical and statistical techniques. The applications to atomic clock development are paralleled by the development of new ways to convert time signals from one form to another, such as from microwave to optical, and by the development of the electronic infrastructure and mathematical techniques for combining and differencing data from nearby clocks.

The high precision and accuracy of atomic clocks has also brought about the need for improved long-distance clock comparisons, referred to as time transfer (time and frequency transfer). Long-distance time transfer is operationally carried out by use of geostationary satellites as well as Global Navigational Satellite Systems, while fiber-optic and free-space time and frequency transfer are under active development and finding more and more operational applications. Conversely, GNSS rely on atomic clocks and their characterization for their continuous day-by-day operations.

The field of time and frequency metrology has followed a kind of Moore’s Law in which the accuracy, frequency, and stability of its techniques have improved by orders of magnitude every few years. We expect this to continue at least for the next decade.

Short-duration Training Events

Professional Meetings

Web-Page Tutorials

Open Source Publications

Books at Graduate Level and above

Refereed Professional Journals

Other Resources