The article from NIST discusses various time and frequency standards, including:
1. Calibration: Comparing a device to an established standard like UTC (NIST) to determine its time and frequency offset with measurement uncertainty.
2. Carrier Frequency: The base frequency of a transmitted signal, often used for frequency calibration. Examples include WWVB (60 kHz), WWV (2.5-20 MHz), WWVH (2.5-15 MHz), and GPS (1575.42 MHz, 1227.6 MHz).
3. Cesium Beam Oscillator: A primary frequency standard using cesium atoms. The atoms are heated, cooled, and exposed to microwave radiation in a vacuum tube. The oscillator’s frequency is derived from a quartz oscillator and has a stability of 5 × 10^-12 at 1 second, improving to a few parts in 10^14 after one day.
4. Cesium Fountain Oscillator: The current state-of-the-art cesium oscillator, named NIST-F2. It uses laser-cooled cesium atoms in a fountain-like motion through a microwave cavity. The Q is about 10^10, with a combined frequency uncertainty near 1 × 10^-16.
The article provides detailed descriptions of these standards, their operation, and their technical specifications.
Keywords: Atom, Frequency, Quartz, Cesium
