Cryogenic whispering gallery sapphire oscillator using 4 K pulse-tube cryocooler

A cryogenic whispering gallery sapphire resonator oscillator has been investigated using a 4 K pulse-tube cryocooler. The turnover temperature of the chosen mode in the sapphire crystal was 9.169 K with an unloaded Q-factor of 7/spl times/10/sup 8/. The prototype SLC oscillator was designed to oscillate at 9.195 GHz and exhibited a fractional frequency stability of 2/spl times/10/sup -13/ at integration times of 10 s. We project a fractional frequency stability better than 1 part in 10/sup -14/ for integration times of 1 s to 100 s with a better temperature stabilized housing and with improved vibration isolation.