Further improvements to NIST-F1. (News Briefs).

NIST scientists have made several improvements to NISTs primary frequency standard, the cesium-fountain clock NIST-F1. The result is improved reliability of operation and improved accuracy. Reliability is important since the value of NIST data submitted to the BIPM is substantially higher if data are submitted at regular intervals. Furthermore, the achievement of highly regular operation offers the opportunity to use the data from this standard directly in the NIST time scale.

The improvements include: installation of new light shutters of substantially higher reliability; implementation of a servo-control system on the number of atoms tossed in each ball; a lower noise quartz-crystal local oscillator; and new software for the main line-center servo-control system. A completely new laser system (Ti:sapphire) has been acquired, and it will replace the current system as soon as final acceptance testing has been completed.

With these changes, the uncertainty of the standard has been improved from 1.7 X [10.sup.-15] to 1.3 X [10.sup.-15]. This is the best yet reported to the BIPM. Furthermore, quantum-projection noise has now been observed at a level of 30 atoms. This is lower by a factor of two to three than had been seen previously in a fountain frequency standard.

CONTACT: Steven Jefferts, [phone]; [e-mail].