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Search Publications by: Tom Parker (Assoc)

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Displaying 51 - 75 of 134

NIST Cesium Fountains - Current Status and Future Prospects

September 12, 2007
Author(s)
Steven R. Jefferts, Thomas P. Heavner, Thomas E. Parker, Jon H. Shirley
We review the current status of the U.S. Primary Frequency Standard, NIST-F1. NIST-F1 is a laser-cooled cesium fountain based frequency standard with an inaccuracy of less than δ f/f {less than or equal to} 5×10 -16 limited mainly by the radiation field in

Optical frequency standards based on mercury and aluminum ions

September 12, 2007
Author(s)
Wayne M. Itano, James C. Bergquist, Anders Brusch, Scott A. Diddams, Tara M. Fortier, Thomas P. Heavner, Leo W. Hollberg, David Hume, Steven R. Jefferts, Luca Lorini, Thomas E. Parker, Till P. Rosenband, Jason Stalnaker
Single-trapped-ion frequency standards based on a 282 nm transition in 199Hg+ and on a 267 nm transition in 27Al+ have been developed at NIST over the past several years. Their frequencies are measured relative to each other and to the NIST primary

A Theoretical Analysis of Frequency Uncertainty

May 29, 2007
Author(s)
Gianna Panfilo, Thomas E. Parker
In this work we present a preliminary study for the determination of the uncertainty on the frequency in the time measurement. The first part of this paper is dedicated to the theoretical study of the frequency uncertainty applying the law of the

Experimental Analysis of Frequency Transfer Uncertainty

May 29, 2007
Author(s)
Thomas E. Parker, Gianna Panfilo
An experimental analysis of frequency transfer uncertainty is carried out. In situations where more than one transfer techniques are available a first difference statistic is used to determine the type and level of the transfer noise for transfer methods

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

May 29, 2007
Author(s)
Tara M. Fortier, Neil Ashby, James C. Bergquist, Marie Delaney, Scott A. Diddams, Thomas P. Heavner, Leo W. Hollberg, Wayne M. Itano, Steven R. Jefferts, K Kim, Windell Oskay, Thomas E. Parker, Jon H. Shirley, Jason Stalnaker, Filippo Levi, Luca Lorini
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

Absolute frequency measurement of the neutral 40 Ca optical frequency standard at 657 nm based on microkelvin atoms

March 14, 2007
Author(s)
G Wilpers, Christopher W. Oates, Scott A. Diddams, A Bartels, Tara M. Fortier, Windell Oskay, James C. Bergquist, Steven R. Jefferts, Thomas P. Heavner, Thomas E. Parker, Leo W. Hollberg
We report an absolute frequency measurement of the optical clock transition at 657 nm in 40Ca with a relative uncertainty of 7.5x10 -15, the most accurate frequency measurement of a neutral atom optical transition to date. Relative instabilities of 2x10

Precision Atomic Spectroscopy for Improved Limits on Variation of the Fine Structure Constant and Local Position Invariance

February 16, 2007
Author(s)
Tara M. Fortier, Jason Stalnaker, Scott A. Diddams, Neil Ashby, Luca Lorini, Windell Oskay, Marie Delaney, James C. Bergquist, Steven R. Jefferts, Thomas E. Parker, Thomas P. Heavner, Filippo Levi, Jon H. Shirley, Wayne M. Itano, Kyoungsik Kim, Leo W. Hollberg
We report tests of local position invariance (LPI) and the constancy of fundamental constants from measurements of the frequency ratio of the 282-nm $^{199}$Hg$^+$ optical clock transition to the ground state hyperfine splitting in $^{133}$Cs. Analysis of

A Straightforward Frequency-Estimation Technique for GPS Carrier-Phase Time Transfer

September 15, 2006
Author(s)
C Hackman, Judah Levine, Thomas E. Parker, Dirk Piester, Juergen Becker
GPS carrier-phase time transfer (GPSCPTT) offers high frequency stability at short averaging times, approaching a fractional frequency stability of 10 -15 at an averaging time of 1 d. However, a discontinuity occurs in the time-transfer estimates between

A single-atom optical clock with high accuracy

July 14, 2006
Author(s)
Windell Oskay, Scott A. Diddams, Elizabeth A. Donley, Tara M. Fortier, Thomas P. Heavner, Leo W. Hollberg, Wayne M. Itano, Steven R. Jefferts, M J. Jensen, Kyoungsik Kim, F Levi, Thomas E. Parker, James C. Bergquist
For the past fifty years, atomic frequency standards based on the cesium ground-state hyperfine splitting have been the most accurate timepieces in the world. One of the most accurate, current-generation, cesium standards is the NIST-F1 fountain, which has

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

June 5, 2006
Author(s)
Jason Stalnaker, Scott A. Diddams, Leo W. Hollberg, Kyoungsik Kim, Elizabeth A. Donley, Thomas P. Heavner, Steven R. Jefferts, Filippo Levi, Thomas E. Parker, James C. Bergquist, Wayne M. Itano, Marie J. Jensen, Luca Lorini, Windell Oskay, Tara M. Fortier, J Torgerson
We report the technical details specific to our recent measurements of the optical frequency of the mercury single-ion clock in terms of the SI second as realized by the NIST-F1 cesium fountain clock. In these measurements the total fractional uncertainty

Comparison between frequency standards in Europe and the USA at the 10 -15 uncertainty level

February 1, 2006
Author(s)
Joseph Achkar, Andreas Bauch, R Dach, R Hlavac, Luca Lorini, Thomas E. Parker, G. Petit, Dirk Piester, P Uhrich, K Szymaniec
Istituto Elettrotecnico Nazionale Galileo Ferraris (IEN), National Institute of Standards and Technology (NIST), National Physical Laboratory (NPL), Laboratoire National de Metrologie et de Essais?Observatoire de Paris/Systemes de Reference Temps Espace

NIST F1: Recent improvements and a resulting accuracy of df/f=0.53x10 -15

September 13, 2005
Author(s)
Thomas P. Heavner, Steven R. Jefferts, Elizabeth Donley, Jon H. Shirley, Tom Parker
In the last several years we have made many improvements to NIST-F1 (a laser-cooled Cs fountain primary frequency standard) resulting in over a factor of 2 reduction in the uncertainty in the realization of the SI second. The two most recent accuracy

Operation of the NIST-F1 Cesium Fountain Primary Frequency Standard with a Maser Ensemble

September 13, 2005
Author(s)
Thomas E. Parker, Steven R. Jefferts, Thomas P. Heavner, Elizabeth A. Donley
The operation of a caesium fountain primary frequency standard is greatly influenced by the characteristics of two other important capabilities. The first is a stable frequency reference and the second is the frequency-transfer system. A stable frequency

A New Microwave Synthesis Chain for the Primary Frequency Standard NIST-F1

August 29, 2005
Author(s)
Thomas P. Heavner, Steven R. Jefferts, Elizabeth A. Donley, F Levi, Thomas E. Parker
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. This system has been used in two accuracy evaluations of NIST

Sources of Instabilities in Two-Way Time Transfer

August 29, 2005
Author(s)
Thomas E. Parker, Victor S. Zhang
Two-Way Satellite Time and Frequency Transfer (TWSTFT) has become an important component in the international system for comparing time and frequency over long distances. In order to make further improvements in the stability of TWSTFT a more complete

Time and frequency dissemination using GPS: Recent improvements

November 1, 2004
Author(s)
Tom Parker, Demetrios Matsakis
This is an article for a general audience that reviews recent imporvements in time and frequency delivery by the Global Positioning System (GPS). A significant improvement in direct time delivery was achieved when Selective Availability (SA) was turned off