Resonator Power to Frequency Conversion in a Cryogenic Sapphire Oscillator

TL;DR

This paper investigates how power fluctuations in a cryogenic sapphire resonator affect its frequency stability, identifying radiation pressure as a key limiting factor in oscillator performance.

Contribution

It provides the first detailed measurement of power to frequency conversion effects, highlighting radiation pressure as the dominant influence on frequency stability.

Findings

Power to frequency sensitivity of -0.15 Hz/mW

Radiation pressure is the main limiting factor

Temperature effects are secondary

Abstract

We report on the measurement and characterization of power to frequency conversion in the resonant mode of a cryogenic sapphire loaded cavity resonator, which is used as the frequency discriminating element of a loop oscillator circuit. Fluctuations of power incident on the resonator leads to changes in radiation pressure and temperature in the sapphire dielectric, both of which contribute to a shift in the resonance frequency. We measure a modulation and temperature independent radiation pressure induced power to frequency sensitivity of -0.15 Hz/mW and find that this is the primary factor limiting the stability of the resonator frequency.