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

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.