Cryo-cooled sapphire oscillator with ultra-high stability

We present test results and design details for the first short-term frequency standard to achieve ultra-high stability without the use of liquid helium. With refrigeration provided by a commercial cryocooler, the compensated sapphire oscillator (10 K CSO) makes available the superior short-term stability and phase noise performance of cryogenic oscillators without periodic interruptions for cryogen replacement. Technical features of the 10 K CSO include use of a a-stage cryocooler with vibration isolation by helium gas at atmospheric pressure, and a new sapphire/ruby resonator design giving compensated operation at 8-10 K with Q=1-2/spl times/10/sup 9/. Stability of the first unit shows an Allan Deviation of /spl sigma//sub y//spl les/2.5/spl times/10/sup -15/ for measuring times of 200 seconds /spl les//spl tau//spl les/600 seconds. We also present results showing the capability of the 10 K CSO to eliminate local oscillator degradation for atomic frequency standards. Configured as L.O. for the LITS-7 trapped mercury ion frequency standard, the CSO/LITS combination demonstrated a limiting performance of 3.0/spl times/10/sup -14///spl tau//sup 1/2/, the lowest value measured to date for a passive atomic frequency standard, and virtually identical to the value calculated from photon statistics.

[1]  G. J. Dick,et al.  Frequency stability of 1/spl times/10/sup -13/ in a compensated sapphire oscillator operating above 77 K , 1996 .

[2]  A.N. Luiten,et al.  Ultrastable cryogenic sapphire dielectric microwave resonators , 1992, Proceedings of the 1992 IEEE Frequency Control Symposium.

[3]  A. Clairon,et al.  Recent results of the LPTF cesium fountain primary frequency standard , 1995, Proceedings of the 1995 IEEE International Frequency Control Symposium (49th Annual Symposium).

[4]  A. Luiten,et al.  Cryogenic sapphire oscillator with improved frequency stability , 2000, Proceedings of the 2000 IEEE/EIA International Frequency Control Symposium and Exhibition (Cat. No.00CH37052).

[5]  Improved performance of the superconducting cavity maser at short measuring times (atomic frequency standards) , 1990, 44th Annual Symposium on Frequency Control.

[6]  P. Boolchand,et al.  A general purpose cold finger using a vibration‐free mounted He closed‐cycle cryostata) , 1995 .

[7]  Lute Maleki,et al.  A mercury ion frequency standard engineering prototype for the NASA deep space network , 1996, Proceedings of 1996 IEEE International Frequency Control Symposium.

[8]  G. J. Dick,et al.  Cryo-cooled sapphire oscillator for the Cassini Ka-band experiment , 1997, Proceedings of International Frequency Control Symposium.

[9]  D. Blair,et al.  Latest results of the U.W.A. cryogenic sapphire oscillator , 1995, Proceedings of the 1995 IEEE International Frequency Control Symposium (49th Annual Symposium).

[10]  G. J. Dick,et al.  Local Oscillator Induced Instabilities in Trapped Ion Frequency Standards , 1987 .

[11]  J. Krupka,et al.  Sapphire-rutile frequency-temperature compensated whispering gallery microwave resonators , 1997, Proceedings of International Frequency Control Symposium.