Showing papers by "G.J. Dick published in 1994"
01 Jun 1994
TL;DR: The /sup 202/Hg lamp is used for state selection and a helium buffer gas for ion cooling as mentioned in this paper, and a preliminary 9 day comparison between the trapped ion standards, the Allan deviation was /spl sigma/sub y/(/spl tau/)=1/spl times/10/sup -13///spl tAU//sup 1/2/ and a fractional frequency stability of 6/spltimes/10 /sup -16/ measured for averaging times greater than 10/sup 5/ seconds.
Abstract: The /sup 199/Hg/sup +/ research frequency standards LITS-1 and LITS-2 were developed to provide continuous, reliable, high stability performance. For simplicity, a /sup 202/Hg lamp is used for state selection and a helium buffer gas for ion cooling. In a preliminary 9 day comparison between the trapped ion standards, the Allan deviation was /spl sigma//sub y/(/spl tau/)=1/spl times/10/sup -13///spl tau//sup 1/2/ and a fractional frequency stability of 6/spl times/10/sup -16/ measured for averaging times greater than 10/sup 5/ seconds. A 40 day comparison of LITS-2 against an auto-tuned H-maser referenced to UTC-NIST puts an upper limit on long term drift of LITS-2 of 1.2(1.4)/spl times/10/sup -16//day. >
15 citations
01 Jun 1994
TL;DR: In this paper, a whispering gallery sapphire resonator for the dominant (WGH/sub n11/) microwave mode family shows frequency-stable, compensated operation for temperatures above 77 kelvin.
Abstract: 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 kelvin. 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 sapphire's dielectric constant. In experimental tests, the WGH/sub 811/ mode showed a frequency turn-over 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 second /spl les//spl tau//spl les/100 seconds 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/. >
12 citations
01 Jun 1994
TL;DR: In this paper, the authors describe an improvement in the architecture of the physics package used in the linear ion trap (LIT) based frequency standard developed at JPL, which is based on the observation that ions can be moved along the axis of an LIT by applied dc voltages.
Abstract: This article describes an improvement in the architecture of the physics package used in the linear ion trap (LIT) based frequency standard developed at JPL. This new design is based on the observation that ions can be moved along the axis of an LIT by applied dc voltages. The state selection/interrogation region can be separated from the more critical microwave resonance region where the multiplied local oscillator (LO) signal is compared to the stable atomic transition. This separation relaxes many of the design constraints of the present units. Improvements include increased frequency stability, and a substantial reduction in size, mass and cost of the final frequency standard. >
5 citations
01 Jun 1994
TL;DR: The CYRES 2D finite element software package developed at The University of Texas at El Paso has proven invaluable for the analysis and identification of modes and mode families for resonators of various geometries as mentioned in this paper.
Abstract: This paper discusses the demonstrated accuracy and utility of a 2-D finite element methodology for whispering gallery mode sapphire resonators. The mode solutions obtained by the software compared with experimental results for a wheel-shaped sapphire resonator give an error in mode frequency of less than 0.55%. We also show parts per million agreement with analytical solutions for simple geometries such as an empty coaxial resonator. The CYRES 2D FEM software package developed at The University of Texas at El Paso has proven invaluable for the analysis and identification of modes and mode families for resonators of various geometries. The software also shows promise as a tool for optimization of new resonator designs. Current uses include design of optimum sized dielectric resonators for minimized wall losses, and new resonator geometries for temperature compensated resonators. The operational characteristics of the software and the general methodology for use of the software as a laboratory and design tool are discussed. >
4 citations
01 Jun 1994
TL;DR: In this paper, a two-dimensional finite element program called CYRES is presented to compute the electromagnetic resonant frequencies and corresponding modes of cylindrical cavity resonators loaded with anisotropic dielectric.
Abstract: A two-dimensional finite element program called CYRES to compute the electromagnetic resonant frequencies and corresponding modes of cylindrical cavity resonators loaded with anisotropic dielectric is presented. Half of the longitudinal plane of the resonator is analyzed with a two-dimensional mesh assuming a sinusoidal dependence in azimuth. The finite element package consists of PC-based pre- and post-processors, as well as the finite element processor implemented in UNIX. The preprocessor allows for the automatic graphical generation of the finite element mesh. The finite element processor computes the resonant frequencies along with the electromagnetic modes. The postprocessor is used to display the magnetic and electric fields at three different sectional planes of the cylindrical resonator. The display is in the form of color contours representing magnitudes of the field vector, and arrows indicating the three-dimensional orientation of the vector. Visualization is available on longitudinal, transverse and circumferential planes. The numerical results obtained are in excellent agreement with closed form solutions for the empty cavity and coaxial resonator, and with experimental resonant frequency measurements made on a shielded dielectric-loaded sapphire resonator. >
3 citations
27 Jun 1994
TL;DR: In this paper, an improved architecture for a small ion trap based frequency standard was discussed, which will reduce the size and cost of current Hg/sup +/ standards and improve the long term frequency stability.
Abstract: We discuss an improved architecture for a small ion trap based frequency standard. This design will reduce the size and cost of current Hg/sup +/ standards and improve the long term frequency stability. Based on our earlier work, stability of 7/spl times/10/sup -14///spl radic//spl tau/ is anticipated. >
1 citations
01 Jan 1994
TL;DR: In this article, the authors report on the design and test of a whispering gallery sapphire resonator for which the dominant microwave mode family shows frequency-stable, compensated operation for temperatures above 77 kelvin.
Abstract: We report on the design and test of a whispering gallery sapphire resonator for which the dominant microwave mode family shows frequency-stable, compensated operation for temperatures above 77 kelvin.
1 citations
01 Jan 1994
TL;DR: In this article, a whispering gallery sapphire resonator for the dominant (WGH,11) microwave mode family shows frequency-stable, compensated operation for temperatures above 77 kelvin.
Abstract: We report on the design and test of a whispering gallery sapphire resonator for which the dominant (WGH,11) microwave mode family shows frequency-stable, compensated operation for temperatures above 77 kelvin. 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 cop per and sapphire expansion coefficients, tunes the resonator to cancel the temperature variation of sapphire's dielectric constant. In experimental tests, the WGHsl1 mode showed a frequency turn-over 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 X 10-l' for measuring times 1 second 5 7 5 100 seconds with unstabilized resonator housing temperature and a mode Q of 2 x lo6. We project a frequency stability for this resonator with stabilized housing temperature and with a mode Q of lo'.