Measurement of fundamental thermal noise limit in a cryogenic sapphire frequency standard using bimodal maser oscillations

Abstract

We report observations of the Schawlow-Townes noise limit in a cryogenic sapphire secondary frequency standard. The effect causes a fundamental limit to the frequency stability, and was measured through the novel excitation of a bimodal maser oscillation of a Whispering Gallery doublet at $12.04GHz$. The beat frequency of $10kHz$ between the oscillations enabled a sensitive probe for this measurement of fractional frequency instability of $10^{-14}{\tau }^{-1/2}$ with only 0.5 $pW$ of output power.

arXiv commentPublished in PRL 100, 233901 (2008)

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• Influence of the ESR saturation on the power sensitivity of cryogenic sapphire resonators
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• Potential sensitivities to Lorentz violation from nonbirefringent modified Maxwell theory of Auger, HESS, and CTA
• Controlling the Frequency-Temperature Sensitivity of a Cryogenic Sapphire Maser Frequency Standard by Manipulating Fe3+ Spins in the Sapphire Lattice
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