NIST-F1

The clock took fewer than four years to test and build, and was developed by Steve Jefferts and Dawn Meekhof of the Time and Frequency Division of NIST's Physical Measurement Laboratory.

[3] The apparatus consists of an optical molasses made of counter-propagating lasers which cool and trap a gas of cesium atoms.

Depending on the exact frequency of the microwaves, the cesium atoms will reach an excited state.

[1] The evaluated accuracy uB reports of various primary frequency and time standards are published online by the International Bureau of Weights and Measures (BIPM).

[4] It used a model developed by NIST [5] to evaluate Doppler frequency shifts, known as distributed cavity phase, some believe to be incorrect.