Caesium fountain atomic clock
Reloj atómico de fuente de cesio
- Date
- 1989-1999 · confidence high
- Place
- Stanford, California, United States
- Credited to
- Steven Chu, Mark Kasevich and colleagues
- Field
- Knowledge & symbols
What it is
A clock in which laser-cooled caesium atoms are tossed upward and fall back under gravity, so the slow atoms are interrogated twice with an interaction time of about one second. It reached an accuracy of one part in 10¹⁵ and is the primary time standard of national laboratories.
The fountain idea was proposed by Jerrold Zacharias in 1953 and failed because of thermal dispersion; Chu and Kasevich made it work in 1989 with laser-cooled atoms. NIST-F1 (1999) was the first US primary standard of this type.
What it led to
- primary frequency standards (NIST-F1, 1999, and fountain clocks of other countries)
- a more accurate International Atomic Time scale
- satellite clock comparisons between laboratories