This work demonstrates that ultra-low phase-noise oscillators with a single-sideband phase-noise spectral density approaching -160 dBc/Hz at Fourier frequency of 1 kHz can be constructed at microwave ...frequencies (8 to 10 GHz). Such noise performance has been achieved by frequency locking a conventional loop oscillator to a temperature-stabilized sapphire dielectric resonator operating at a relatively high level of dissipated microwave power ( ~ 0.5 W). Principles of microwave circuit interferometry have been employed to generate the error signal for the oscillator frequency control system. No cryogens were used. Two almost identical oscillators were built to perform the classical 2-oscillator phase noise measurements. The phase referencing of one oscillator to another was achieved by varying microwave power dissipated in the sapphire resonator.
Progress in atomic fountains at LNE-SYRTE Guena, J.; Abgrall, M.; Rovera, D. ...
IEEE transactions on ultrasonics, ferroelectrics, and frequency control,
03/2012, Letnik:
59, Številka:
3
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
We give an overview of the work done with the Laboratoire National de Metrologie et d'Essais-Systemes de Reference Temps-Espace (LNE-SYRTE) fountain ensemble during the last five years. After a ...description of the clock ensemble, comprising three fountains, FO1, FO2, and FOM, and the newest developments, we review recent studies of several systematic frequency shifts. This includes the distributed cavity phase shift, which we evaluate for the FO1 and FOM fountains, applying the techniques of our recent work on FO2. We also report calculations of the microwave lensing frequency shift for the three fountains, review the status of the blackbody radiation shift, and summarize recent experimental work to control microwave leakage and spurious phase perturbations. We give current accuracy budgets. We also describe several applications in time and frequency metrology: fountain comparisons, calibrations of the international atomic time, secondary representation of the SI second based on the 87 Rb hyperfine frequency, absolute measurements of optical frequencies, tests of the T2L2 satellite laser link, and review fundamental physics applications of the LNE-SYRTE fountain ensemble. Finally, we give a summary of the tests of the PHARAO cold atom space clock performed using the FOM transportable fountain.
The Axion Dark Matter eXperiment (ADMX) has previously excluded Dine-Fischler-Srednicki- Zhitnisky (DFSZ) axions between 680-790 MHz under the assumption that the dark matter is described by the ...isothermal halo model. However, the precise nature of the velocity distribution of dark matter is still unknown, and alternative models have been proposed. Here, we report the results of a non-virialized axion search over the mass range 2.81–3.31 µeV, corresponding to the frequency range 680–800 MHz. This analysis marks the most sensitive search for non-virialized axions sensitive to Doppler effects in the Milky Way Halo to date. Accounting for frequency shifts due to the detector’s motion through the Galaxy, we exclude cold flow relic axions with a velocity dispersion of $\mathscr{O}$(10-7)c with 95% confidence.
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