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.

Published in PRL 100, 233901 (2008)

References in corpus (1)

• Test of Lorentz Invariance in Electrodynamics Using Rotating Cryogenic Sapphire Microwave Oscillators