Cryogenic sapphire oscillator using a low- vibration design pulse-tube cryocooler: first results

A cryogenic sapphire oscillator (CSO) 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 ¿
_y
= 1.4 × 10
^-5
¿
^-1/2
for integration times 1 < ¿ < 10 s, dominated by white frequency noise. The minimum ¿
_y
= 5.3 × 10
^-16
for the two oscillators was reached at ¿ = 20 s. Assuming equal contributions from both CSOs, the single oscillator phase noise S
_¿
¿ -96 dB.rad
²
/Hz at 1 Hz set from the carrier.