title: Measurement of the 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 12.04 GHz. The beat frequency of 10 kHz 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.
authors.affiliation: Institut FEMTO-ST, UMR 6174 CNRS, Université de Franche, Comté, Besançon, France.
authors.forename: Karim
authors.initials: K
authors.lastname: Benmessai
authors.forename: Daniel Lloyd
authors.initials: DL
authors.lastname: Creedon
authors.forename: Michael Edmund
authors.initials: ME
authors.lastname: Tobar
authors.forename: Pierre-Yves
authors.initials: PY
authors.lastname: Bourgeois
authors.forename: Yann
authors.initials: Y
authors.lastname: Kersalé
authors.forename: Vincent
authors.initials: V
authors.lastname: Giordano