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

TL;DR

This paper demonstrates the measurement of the fundamental thermal noise limit in a cryogenic sapphire frequency standard by exciting bimodal maser oscillations, achieving high sensitivity in frequency stability assessment.

Contribution

It introduces a novel method using bimodal maser oscillations to measure the Schawlow-Townes noise limit in a cryogenic sapphire frequency standard.

Findings

Measured fractional frequency instability of 10^{-14} at 1 second.

Achieved this with only 0.5 pW of output power.

Demonstrated a new sensitive approach for fundamental noise measurement.

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.