Initial evaluation of the USNO rubidium fountain

We discuss the first rubidium atomic fountain at the U. S. Naval Observatory, NRF1, which has been built as a prototype for future devices to be included in the USNO timescale. The system has demonstrated a short-term Allan deviation of 1.35×10
¹³
/τ
^1/2
when measured against a hydrogen maser. We have directly compared NRF1's performance to that of our cesium fountain, NCF, demonstrating integration as 1/τ
^1/2
below 1×10
^-15
, and performance that is consistent with 7×10
^-16
at 11 hours.