"Laser-Cooled Primary Frequency Standards at NIST" by Dr. Steven Jefferts
March 29, 2011 - 7:00am
NIST-F1, a cesium fountain frequency standard which serves as the US primary frequency standard has been operating for several years with fractional frequency uncertainties of . The uncertainties in NIST-F1 are limited primarily by the blackbody radiation shift caused by the room temperature environment of the fountain. We have begun operation of NIST-F2 with preliminary uncertainties in the region of . NIST-F2 uses a novel cryogenic structure to reduce the blackbody radiation shift to negligible levels and should be capable of operation at the level. Recent comparisons between NIST F1&F2 show no significant disagreement at the level, which serves as the best measurement to date of the blackbody radiation shift. We will review the operation of both cesium fountains and present preliminary results of comparisons between the two.