The subject invention relates to an improved microwave cavity reso­nator 35 and internal magnetic shield of small design for use with an atomic frequency standard. In an embodiment for an optical-­physics package 10 the invention comprises a light source 11, a cell 25 having a predetermined volume in which atoms are contained capable of undergoing a hyperfine transition within a microwave region of the spectrum and disposed to receive the light from said source 11, a microwave cavity resonator 35 composed of a ferro-­magnetic or magnetically equivalent material and having a cavity substantially commensurate in volume with the predetermined cell volume, means 16 for detecting the light transmitted through said cell 25 and producing a detection signal representing the trans­mission of light therethrough, means 31 for subjecting the cell 25 within said cavity to electromagnetic waves inducing the hyperfine transition of the atoms to increase the absorption of the light, means 19 for applying a magnetic field to the cell 25 to provide a substantial bias field to said cavity, said means 19 for applying said magnetic field being generated within the cavity, and control means 21, 26, 27 responsive to the detection signal for modifying the frequency of said electromagnetic waves so as to steer and maintain their frequency substantially centered on the frequency of the hyperfine transition of said atoms.

Integrated microwave cavity resonator and magnetic shield for an atomic frequency standard

An ultra-miniature, general-purpose rubidium gas cell frequency standard with a two-cell scheme has been successfully developed, with the aim of developing one of the smallest atomic frequency standards in the world. The target volume of the new rubidium frequency standard is less than 100 cm/sup 3/. It is assumed that the shape of oscillator enables to mount on a printed circuit board. In order to miniaturize the volume and height, the physics package is made small. Because the frequency of the cavity resonator is 6.834 GHz and the resonator mode is TE/sub 111/, the inside diameter of the cavity needs to be 26 mm. To reduce the inside diameter, a new cavity resonator, which contains a dielectric material, has been developed. As a result, an inside diameter of 16 mm and a capacity of 6.7 cm/sup 3/ are achieved. The total size of the physics package, which contains a rubidium-lamp exciter, a preamplifier, and a single magnetic shield of mumetal, is reduced to 25 cm/sup 3/. By applying the PLL method, instead of the conventional frequency multiplier for a high frequency circuit that generates resonance frequency of 6.834 GHz from a slave oscillator, the size and cost of the circuit are minimized. As for the reduction of the power consumption, a new switching regulator IC is adopted in the power circuit. In addition, with the use of DDS, it enables to set the output frequency within the range of 1 to 15 MHz. Because of these features, the new rubidium frequency standard is extremely small in volume (95 cm/sup 3/), and lightweight (180 grams).

An ultra-miniature rubidium frequency standard

With the goal of minimizing the overall size of a gas cell frequency standard the authors have characterized cylindrical Cs cells with inner dimensions R=2 mm and L=18 mm. Under conditions of present interest the lifetime in the absence of a tuned microwave field tends to be dominated by Cs-Cs collisions. Wall collisions have only a marginal effect on the lifetime, provided appropriate conditions on the N/sub 2//Ar buffer gas pressure, are satisfied. Using a Te/sub 101/ mode rectangular cavity the microwave resonance lineshape signal parameters were measured over a range of optical and microwave powers at various cell temperatures and used to predict the achievable short term stability. For the optimum combination of optical and microwave powers the linewidth is dominated by power broadening, and the short term stability, sigma ( tau ), predicted from these measurements decreases from sigma ( tau ) tau /sup 1/2/=6.4*10/sup -12/ to 4.2*10/sup -12/, where tau is in seconds, as the cell cold spot temperature is raised from 50 degrees C to 65 degrees C. >

Towards a miniature laser-pumped cesium cell frequency standard

An ultra-miniature, general-purpose rubidium gas cell frequency standard with a two-cell scheme has been successfully developed, with the aim of developing one of the smallest atomic frequency standards in the world. The new rubidium frequency standard embodies new electrical and structural design features, such as a miniature physics package incorporating a cylindrical TE111 microwave cavity in which an integrated filter-resonance cell is entirely loaded, a 10MHz ultra-miniature slave oscillator using voltage controlled TCXO(VC-TCXO) technologies established in the mobile telecommunication field, state of-the-art electronic circuit/assembly technologies, and a simplified, fabrication-oriented structure. As a result of these features, the new rubidium standard has an extremely small volume (310 cc), light weight (700 grams), and a wide operating temperature range (-10 degree C to +60 degree C). A series of measurements have been made to characterize the performance of the new rubidium frequency standard. In spite of the substantial reduction in size, it exhibits excellent performance, comparable to that of existing high performance models of commercial rubidium frequency standards, including previous models which Fujitsu has developed. Presented in this paper are the details of the design concepts and electronic performance of this newly-developed frequency standard.

An ultra-miniature rubidium frequency standard with two-cell scheme

The slow-wave structure (SWS) can be used as the resonant cavity for rubidium atomic frequency standards (RAFSs), in which the longitudinal component of the magnetic field can enable the rubidium atoms' participation in the stimulated transitions. In this paper, an improved helix SWS based on good propagation characteristics as a helical resonator for RAFS is designed. The theoretical analysis is performed together with the simulations of the propagation characteristics. Using finite integration technique (FIT), the simulated results, including phase velocity, on-axis interaction impedance, and distribution of the magnetic field, are implemented and compared with the experimented results. The effects of the different helical pitch and dielectric material in the insulator cylinder on the propagation characteristics are analyzed in detail. The analyzed results show that smaller helical pitch and proper usage of dielectric material in the insulator cylinder can make the propagation characteristics of the helix SWS superior. The improved helix SWS for RAFS adapts a smaller helical pitch and is loaded with the dielectric material of Teflon in the insulator cylinder. This structure can reduce the cavity volume to 14.7 cm3. The short-term stability of RAFS is up to 1.28 × 10-12/?1/2, and the frequency stability is 2.0 × 10-10/°C at the temperature range of -20°C to +55°C.

An Improved Helical Resonator Design for Rubidium Atomic Frequency Standards

An u l t r a -min ia tu re , gene ra l -pu rpose rub id ium gas ce l l f r equency s t anda rd has been des igned and i n v e s t i g a t e d e x p e r i m e n t a l l y , w i t h t h e aim of deve loping one of the smallest atomic frequency s t anda rds ye t deve loped . Th i s pape r desc r ibes t h e d e t a i l s o f t h e d e s i g n c o n c e p t and t h e e x p e r i mental results ob ta ined so f a r .

K. Chiba

Papers

An Ultra-Miniature Rubidium Frequency Standard