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 $σ_y = 1.4 \times 10^{-15}τ^{-1/2}$ for integration times $1 < τ< 10$ s, dominated by white frequency noise. The minimum $σ_y = 5.3 \times 10^{-16}$ for the two oscillators was reached at $τ= 20$ s. Assuming equal contributions from both CSOs, the single oscillator phase noise $S_ϕ \approx -96 \; dB \; rad^2/Hz$ at 1 Hz offset from the carrier.

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