# Référence Secondaire de Fréquence à Résonateur Saphir Cryogénique

Abstract : This thesis is devoted to the realization and the characterization of a cryogenic microwave secondary frequency standard for metrological applications.\\ This standard is based on the excitation of a high-order electromagnetic mode, of the whispering-gallery'' type, within a cylindrically shaped piece of monocrystalline sapphire ($Al_2O_3$) maintained at a temperature near to that of liquid helium.\\ Such a resonator currently represents the best solution to realizing frequency stabilities of the order of $1\cdot 10^(-14)$.\\ Mode splitting is generally observed at cryogenic temperatures, which makes the adjustment of the coupling difficult. We present a simple model that successfully explains the observed degeneracy and lineshapes for each mode. Moreover, we solve the problem of spurious modes by placing the resonator in an open cavity.\\ Every component needed for constructing a frequency-stable microwave oscillator based around the cryogenic resonator is analysed in detail.\\ The experimental results we obtain are exceptional: the oscillator realizes a short-term fractional frequency instability of less than $7.5\cdot 10^(-15)$. Over the longer term, any frequency drift is clearly identifiable; the instability at one-day intervals lies below $2\cdot 10^(-14)$. This last result represents the state of the art for long-term secondary frequency standards. \\ Several other, related pieces of work are also presented: the measurement of the dielectric properties of a langasite crystal, the characterization of ultra-stable oscillators, a sapphire-rutile composite resonator oscillator, a synthesis chain, and the observation of a bistability phenomenon due to the accidental coincidence of a whispering gallery mode with the paramagnetic resonance of $Fe^(3+)$ ions within the sapphire crystal.
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https://tel.archives-ouvertes.fr/tel-00008331
Contributor : Pierre-Yves Bourgeois <>
Submitted on : Wednesday, April 6, 2005 - 3:34:32 AM
Last modification on : Thursday, November 12, 2020 - 9:42:07 AM
Long-term archiving on: : Monday, September 20, 2010 - 12:11:15 PM

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• HAL Id : tel-00008331, version 2

### Citation

Pierre-Yves Bourgeois. Référence Secondaire de Fréquence à Résonateur Saphir Cryogénique. Autre. Université de Franche-Comté, 2004. Français. ⟨tel-00008331v2⟩

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