A post-processed time scale, involving an ensemble of five hydrogen masers, has been developed by a NIST scientist in Boulder to serve as a reference for comparing primary frequency standards
. During the last 2 years, this time scale has been used to evaluate the relative frequencies of NIST-7, an optically pumped cesium-beam standard, and NIST-F1, the cesium-fountain frequency standard
The unit is primarily a stable frequency standard
. Once the unit is disciplined, the GPS signal can be removed for several days with only minor interim degradation to frequency accuracy.
Key words: atomic clock; atomic frequency standard
; cesium-beam frequency standard
; cesium-fountain frequency standard
; clock; fountain frequency standard
; frequency; frequency standard
; ion frequency standard
; lasercooling of atoms; stored-ion frequency standard
The rubidium frequency standard
uses the property of atomic resonance in a rubidium physics package to control the output frequency of a 50.225+ MHz voltage controlled crystal oscillator (VCXO) via frequency locked-loop (FLL).
This transition is under investigation as an optical frequency standard
. The perturbations calculated are the quadratic Zeeman shift, the scalar and tensor quadratic Stark shifts, and the interaction between an external electric field gradient and the atomic quadmpole moment.
The frequencies are derived from an internal temperature controlled crystal oscillator or from an external frequency standard
Scientists at NIST (Boulder) are using the results to estimate the shift due to external fields that might be expected to occur in an optical frequency standard
based on the [Hg.sup.+] transition at 281.5 nm; this is one of the most precise frequency standards
currently under development.
With a 10 MHz OCXO frequency standard
and 0.1 Hz resolution, the instrument is priced at $11,500.
The new technology could allow scientists anywhere to access the frequency standard
simply by tapping into the telecommunications network.