Cryogenic Sapphire Oscillator using a low-vibration design pulse-tube cryocooler: First results

TL;DR

This paper reports the development of a cryogenic sapphire oscillator using a low-vibration pulse-tube cryocooler, achieving frequency stability comparable to liquid helium cooled systems, with detailed noise performance analysis.

Contribution

First implementation of a cryogenic sapphire oscillator at 11.2 GHz using a low-vibration pulse-tube cryocooler with performance comparable to liquid helium cooled systems.

Findings

Frequency instability of 1.4×10^{-15} at 1 second

Minimum instability of 5.3×10^{-16} at 20 seconds

Single oscillator phase noise approximately -96 dB rad^2/Hz at 1 Hz offset

Abstract

A Cryogenic Sapphire Oscillator has been implemented at 11.2 GHz using a low-vibration design pulse-tube cryocooler. Compared with a state-of-the-art liquid helium cooled CSO in the same laboratory, the square root Allan variance of their combined fractional frequency instability is $\sigma_y = 1.4 \times 10^{-15}\tau^{-1/2}$ for integration times $1 < \tau < 10$ s, dominated by white frequency noise. The minimum $\sigma_y = 5.3 \times 10^{-16}$ for the two oscillators was reached at $\tau = 20$ s. Assuming equal contributions from both CSOs, the single oscillator phase noise $S_{\phi} \approx -96 \; dB \; rad^2/Hz$ at 1 Hz offset from the carrier.