Search results for: S.R. Jefferts

Items from 1 to 15 out of 15 results

article

Cryogenic fountain development at NIST and INRIM: preliminary characterization

F. Levi, C. Calosso, D. Calonico, L. Lorini, more

IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control > 2010 > 57 > 3 > 600 - 605

This paper describes the new twin laser-cooled Cs fountain primary frequency standards NIST-F2 and ITCsF2, and presents some of their design features. Most significant is a cryogenic microwave interrogation region which dramatically reduces the blackbody radiation shift. We also present a preliminary accuracy evaluation of IT-CsF2.

chapter

The cryogenic fountain ITCsF2

F. Levi, C. Calosso, D. Calonico, L. Lorini, more

2009 IEEE International Frequency Control Symposium Joint with the 22nd European Frequency and Time forum > 769 - 773

2009 Joint Meeting of the European Frequency and Time Forum (EFTF'09) and the IEEE International Frequency Control Symposium (FCS'09)

This paper describes the new twin laser-cooled Cs fountain primary frequency standards NIST-F2 and IT-CsF2, and presents their most innovative design features. Most significant is a cryogenic microwave interrogation region which dramatically reduces the blackbody radiation shift. We present as well a preliminary accuracy evaluation of IT-CsF2.

article

First-Order Sideband Pulling in Atomic Frequency Standards

J.H. Shirley, T.P. Heavner, S.R. Jefferts

IEEE Transactions on Instrumentation and Measurement > 2009 > 58 > 4 > 1241 - 1246

Many high-performance atomic frequency standards, including cesium fountains and most optical standards, operate with pulsed measurements, that is, an atomic sample is prepared for measurement, the measurement is made, and the process is repeated at fixed intervals. By introducing frequency modulation of the excitation coherent with the measurement cycle time, we have observed biases in our primary...

chapter

First-order sideband pulling in atomic frequency standards

J.H. Shirley, T.P. Heavner, S.R. Jefferts

2008 Conference on Precision Electromagnetic Measurements Digest > 60 - 61

2008 Conference on Precision Electromagnetic Measurements

High performance frequency standards, including cesium fountains and most optical standards, operate with pulsed measurements repeated at a fixed frequency. By introducing frequency modulation of the excitation coherent with the measurement cycle time, we have observed biases in the primary frequency standard NIST-F1 much larger than biases predicted by previous theories. We derive a theory of such...

chapter

Improved Limits on Variation of the Fine Structure Constant and Violation of Local Position Invariance

T.M. Fortier, N. Ashby, J.C. Bergquist, M.J. Delaney, more

2007 IEEE International Frequency Control Symposium Joint with the 21st European Frequency and Time Forum > 663 - 665

2007 IEEE International Frequency Control Symposium Jointly with the 21st European Frequency and Time Forum

We report tests of Local Position Invariance (LPI) and constancy of fundamental constants from measurements of the frequency ratio of the 282-nm 199Hg+ optical clock transition to the ground-state hyperfine splitting in 133Cs. Analysis of the frequency ratio, extending over six years at NIST, is used to place a limit on the fractional variation of the two clocks of less than 5.8??10-6 per change in...

chapter

Testing Local Position Invariance with Four H Masers and Four Cs Fountains

N. Ashby, T.P. Heavner, S.R. Jefferts, A.G. Radnaev, more

2007 IEEE International Frequency Control Symposium Joint with the 21st European Frequency and Time Forum > 355 - 356

2007 IEEE International Frequency Control Symposium Jointly with the 21st European Frequency and Time Forum

We report the most sensitive tests to date of the assumption of local position invariance (LPI) underlying general relativity, based on a 7 yr comparison of cesium and hydrogen atomic clocks (frequency standards). The latest results place an upper limit that is over 20 times smaller than the previous most sensitive tests; this is consistent with the null shift predicted by LPI. The result is based...

article

Optical-to-microwave frequency comparison with fractional uncertainty of 10^-15

J.E. Stalnaker, S.A. Diddams, T.M. Fortier, K. Kim, more

Applied Physics B > 2007 > 89 > 2-3 > 167-176

We report the technical aspects of the optical-to-microwave comparison for our recent measurements of the optical frequency of the mercury single-ion frequency standard in terms of the SI second as realized by the NIST-F1 cesium fountain clock. Over the course of six years, these measurements have resulted in a determination of the mercury single-ion frequency with a fractional uncertainty of less...

chapter

Frequency Biases in Pulsed Atomic Fountain Frequency Standards Due to Spurious Components in the Microwave Spectrum

T.P. Heavner, J.H. Shirley, F. Levi, D. Yu, more

2006 IEEE International Frequency Control Symposium and Exposition > 273 - 276

Proceedings of the 2006 IEEE International Frequency Control Symposium and Exposition

A mechanism by which spurs in the microwave spectrum may cause biases in pulsed atomic fountain frequency standards was identified by Levi et al. Here we present models for the cases of phase modulating (PM) and amplitude modulating (AM) spurs in the spectrum. In the case of a PM spur, the bias is first-order in the spur amplitude. Under common experimental conditions, this effect may be much larger...

chapter

Absolute Optical Frequency Measurements with a Fractional Frequency Uncertainty at 1 ?? 10^-15

J.E. Stalnaker, S.A. Diddams, K. Kim, L. Hollberg, more

2006 IEEE International Frequency Control Symposium and Exposition > 462 - 469

Proceedings of the 2006 IEEE International Frequency Control Symposium and Exposition

We report the technical details specific to our recent measurements of the optical frequency of the mercury single-ion frequency standard in terms of the SI second as realized by the NIST-F1 cesium fountain clock. In these measurements the total fractional uncertainty is ap 10^-15, limited by the statistical measurement uncertainty. In this paper we will address the techniques employed for the optical-to-microwave...

chapter

Power dependence of the shift caused by spurious spectral components in atomic fountain

F. Levi, J.H. Shirley, T.P Heavner, Dai-Hyuk Yu, more

Proceedings of the 20th European Frequency and Time Forum > 181 - 185

2006 20th European Frequency and Time Forum (EFTF)

In this paper we analyze the behavior of the frequency shift caused by a spurious spectral component in the microwave spectrum against variation of the excitation microwave field. The theory of the shift caused by the presence of spurs in the microwave spectrum was investigated in depth over many years, however for historical reasons the behavior was never analyzed when microwave power is varied far...

article

Power dependence of distributed cavity phase-induced frequency biases in atomic fountain frequency standards

S.R. Jefferts, J.H. Shirley, N. Ashby, E.A. Burt, more

IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control > 2005 > 52 > 12 > 2314 - 2321

We discuss the implications of using high-power microwave tests in a fountain frequency standard to measure the frequency bias resulting from distributed cavity-phase shifts. We develop a theory which shows that the frequency bias from distributed cavity phase depends on the amplitude of the microwave field within the cavity. The dependence leads to the conclusion that the frequency bias associated...

chapter

A new microwave synthesis chain for the primary frequency standard NIST-F1

T.P. Heavner, S.R. Jefferts, E.A. Donley, T.E. Parker, more

Proceedings of the 2005 IEEE International Frequency Control Symposium and Exposition, 2005. > 308 - 311

2005 IEEE International Frequency Control Symposium and Exhibition

We present the design and measurements of the microwave synthesis chain presently used in NIST-F1, the laser-cooled cesium fountain primary frequency standard in operation at NIST, Boulder, CO. The chain has been used in two accuracy evaluations of NIST-F1 (January 2005 and July 2005), each of which had a combined (type A and type B) fractional frequency uncertainty of ~ 0.5 times 10^-15. Additionally,...

article

PARCS: NASA’s laser-cooled atomic clock in space

D.B. Sullivan, N. Ashby, E.A. Donley, T.P. Heavner, more

Advances in Space Research > 2005 > 36 > 1 > 107-113

The Primary Atomic Reference Clock in Space (PARCS) mission is designed to perform certain tests of relativity theory, to study the performance of individual GPS space-vehicle clocks, to study the dynamics of atom motion in microgravity, to advance the state-of-the art for space clocks, and to serve as a pathfinder for precision instruments based on laser cooling of atoms. After a brief overview of...

chapter

Recent Improvements in NIST-Fl and Resulting Accuracies of δf/f<7x10^-16

T.P. Heavner, S.R. Jefferts, E.A. Donley, J.H. Shirley, more

2004 Conference on Precision Electromagnetic Measurements > 498 - 499

2004 Conference on Precision electromagnetic Digest

Since our last publication describing the accuracy budget for NIST-FI (a laser-cooled Cs fountain primary frequency standard) the authors have made many improvements resulting in nearly a factor of 2 reduction in the uncertainty in the realization of the SI second. Recently the authors reported a combined standard fractional uncertainty of 0.67times10^-15

article

Measurement of dynamic end-to-end cavity phase shifts in cesium-fountain frequency standards

S.R. Jefferts, T.P. Heavner, E.A. Donley, T.E. Parker

IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control > 2004 > 51 > 6 > 652 - 653

We have measured a previously unobserved systematic frequency shift in our cesium-fountain frequency standard, NIST-F1. This shift, predicted theoretically previously, mimics the well-known end-to-end phase shift in atomic beam standards when synchronous thermal transients are present. Detuning the microwave cavity several megahertz from resonance reduces this effect to the /spl delta/f/f=10/sup -16/...

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Search results for: S.R. Jefferts

Cryogenic fountain development at NIST and INRIM: preliminary characterization

The cryogenic fountain ITCsF2

First-Order Sideband Pulling in Atomic Frequency Standards

First-order sideband pulling in atomic frequency standards

Improved Limits on Variation of the Fine Structure Constant and Violation of Local Position Invariance

Testing Local Position Invariance with Four H Masers and Four Cs Fountains

Optical-to-microwave frequency comparison with fractional uncertainty of 10^-15

Frequency Biases in Pulsed Atomic Fountain Frequency Standards Due to Spurious Components in the Microwave Spectrum

Absolute Optical Frequency Measurements with a Fractional Frequency Uncertainty at 1 ?? 10^-15

Power dependence of the shift caused by spurious spectral components in atomic fountain

Power dependence of distributed cavity phase-induced frequency biases in atomic fountain frequency standards

A new microwave synthesis chain for the primary frequency standard NIST-F1

PARCS: NASA’s laser-cooled atomic clock in space

Recent Improvements in NIST-Fl and Resulting Accuracies of δf/f<7x10^-16

Measurement of dynamic end-to-end cavity phase shifts in cesium-fountain frequency standards

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