Atomic Fountain

Caesium clock geometry in which a laser-cooled cloud is launched upward, giving ~1 s interrogation times and 10⁻¹⁶-level stability.

Specifications & Metrics

A cooled atomic cloud launched in a fountain allows wait times on the order of one second.
That gives much higher frequency resolution than a hot atomic beam, whose interaction times are on the order of tens of microseconds.
NIST-F1, a caesium fountain clock, operates with a fractional instability of 2×10⁻¹⁶.