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 $\sigma_y = 1.4 \times 10^{-15}\tau^{-1/2}$forintegrationtimes$1 < \tau < 10$ 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.