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61.
Absolute frequency measurements of the Hg+ and Ca optical clock transitions with a femtosecond laser
Udem T Diddams SA Vogel KR Oates CW Curtis EA Lee WD Itano WM Drullinger RE Bergquist JC Hollberg L 《Physical review letters》2001,86(22):4996-4999
The frequency comb created by a femtosecond mode-locked laser and a microstructured fiber is used to phase coherently measure the frequencies of both the Hg+ and Ca optical standards with respect to the SI second. We find the transition frequencies to be f(Hg) = 1 064 721 609 899 143(10) Hz and f(Ca) = 455 986 240 494 158(26) Hz, respectively. In addition to the unprecedented precision demonstrated here, this work is the precursor to all-optical atomic clocks based on the Hg+ and Ca standards. Furthermore, when combined with previous measurements, we find no time variations of these atomic frequencies within the uncertainties of the absolute value of( partial differential f(Ca)/ partial differential t)/f(Ca) < or =8 x 10(-14) yr(-1) and the absolute value of(partial differential f(Hg)/ partial differential t)/f(Hg) < or =30 x 10(-14) yr(-1). 相似文献
62.
Kimmo A Michelsen Daniël LA van den Hove Christoph Schmitz Olivier Segers Jos Prickaerts Harry WM Steinbusch 《BMC neuroscience》2007,8(1):107
Background
Both prenatal stress (PS) and postnatal chronic mild stress (CMS) are associated with behavioral and mood disturbances in humans and rodents. The aim of this study was to reveal putative PS- and/or CMS-related changes in basal spine morphology and density of pyramidal neurons in the rat medial prefrontal cortex (mPFC). 相似文献63.
J.E. Stalnaker S.A. Diddams T.M. Fortier K. Kim L. Hollberg J.C. Bergquist W.M. Itano M.J. Delany L. Lorini W.H. Oskay T.P. Heavner S.R. Jefferts F. Levi T.E. Parker J. Shirley 《Applied physics. B, Lasers and optics》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 than 7×10-16, making it the most accurately measured optical frequency to date. In this paper, we focus on the details of the comparison
techniques used in the experiment and discuss the uncertainties associated with the optical-to-microwave synthesis based on
a femtosecond laser frequency comb. We also present our most recent results in the context of the previous measurements of
the mercury single-ion frequency and arrive at a final determination of the mercury single-ion optical frequency: f(Hg+)=1 064 721 609 899 145.30(69) Hz.
PACS 06.30.Ft; 42.62.Eh; 32.30.Jc 相似文献