D.G. Santiago

Temperature-compensated sapphire resonator for ultra-stable oscillator capability at temperatures above 77 K

We report on the design and test of a whispering gallery sapphire resonator for which the dominant (WGH/sub n11/) microwave mode family shows frequency-stable, compensated operation for temperatures above 77 K. The resonator makes possible a new ultra-stable oscillator (USO) capability that promises performance improvements over the best available crystal quartz oscillators in a compact cryogenic package. A mechanical compensation mechanism, enabled by the difference between copper and sapphire expansion coefficients, tunes the resonator to cancel the temperature variation of sapphires dielectric constant. In experimental tests, the WGH/sub 811/ mode showed a frequency turnover temperature of 87 K in agreement with finite element calculations. Preliminary tests of oscillator operation show an Allan Deviation of frequency variation of 1.4-6/spl times/10/sup -12/ for measuring times 1 s /spl les//spl tau//spl les/100 s with unstabilized resonator housing temperature and a mode Q of 2/spl times/10/sup 6/. We project a frequency stability 10/sup -14/ for this resonator with stabilized housing temperature and with a mode Q of 10/sup 7/. >

A mercury ion frequency standard engineering prototype for the NASA deep space network

An engineering prototype linear ion trap frequency standard (LITS-4) using /sup 199/Hg/sup +/ is operational and currently under test for NASAs Deep Space Network (DSN). The DSN requires high stability and reliability with continuous operation. For practical considerations optical pumping and atomic state selection are accomplished with a /sup 202/Hg/sup +/ RF discharge lamp, and the trapped ions are cooled to near room temperature using a helium buffer gas. The standard is closely modeled from earlier research standards LITS-1 and LITS-2 which have demonstrated excellent frequency stability for uninterrupted comparison intervals up to 5 months. During an initial 135 day test in the DSN, LITS-4 operated continuously using a quartz crystal as the local oscillator. Recent signal to noise measurements indicate that a short term stability of /spl sigma//sub y/(/spl tau/)=2.0/spl times/10/sup -14///spl tau//sup 1/2/ can be achieved when operated with a sufficiently stable local oscillator.

Improved performance of a temperature compensated LN/sub 2/ cooled sapphire oscillator

We report on improved stability in a whispering gallery sapphire resonator for which the dominant WGH/sub nll/ microwave mode family shows frequency-stable, compensated operation for temperatures above 77 K. Several modifications during the past year have led to significant improvements in performance. Current tests with improved thermal stability provide Allan Deviation of frequency of 2.6-4/spl middot/10/sup -13/ for measurement times of 1/spl les//spl tau//spl les/100 seconds. We project a frequency stability of 10/sup -14/ for this resonator with stabilized housing temperature and with a mode Q of 10/sup 7/.

Temperature compensated sapphire resonator for ultra-stable oscillator capability at temperatures above 77 kelvin

We report on the design and test of a whispering gallery sapphire resonator for which the dominant (WGH/sub n11/) microwave mode family shows frequency-stable, compensated operation for temperatures above 77 K. The resonator makes possible a new ultra-stable oscillator (USO) capability that promises performance improvements over the best available crystal quartz oscillators in a compact cryogenic package. A mechanical compensation mechanism, enabled by the difference between copper and sapphire expansion coefficients, tunes the resonator to cancel the temperature variation of sapphires dielectric constant. In experimental tests, the WGH/sub 811/ mode showed a frequency turnover temperature of 87 K in agreement with finite element calculations. Preliminary tests of oscillator operation show an Allan Deviation of frequency variation of 1.4-6/spl times/10/sup -12/ for measuring times 1 s /spl les//spl tau//spl les/100 s with unstabilized resonator housing temperature and a mode Q of 2/spl times/10/sup 6/. We project a frequency stability 10/sup -14/ for this resonator with stabilized housing temperature and with a mode Q of 10/sup 7/.<<ETX>>