Showing papers by "Fred L. Walls published in 1981"

Proposed Stored 201 Hg + Ion Frequency Standards

Abstract: Frequency and Time Standards Group Time and Frequency D i v i s i o n National Bureau of Standards Boulder, Colorado 80303 Summary method for h igh-res lu t ion spect roscopy, ' it has been c lea r tha t t hese techn iques p rov ide the bas i s 210 I n t h i s paper, we discuss the performance p o t e n t i a l and the problems o f implement ing a for n excel lent t ime and frequency standard. microwave frequency '(and t ime) standard $n& an o p t i c a l f r e q u e n c y s t a n d a r d u t i l i z i n g 201Hg ions s t o r e d i n a Penning trap. Many o f t he d i scuss ions app ly to ion s to rage-based f requency s tandards in genera l . Laser cool ing, opt ica l pumping, and o p t i c a l d e t e c t i o n o f t h e m i c r o w a v e o r o p t i c a l c l o c k t r a n s i t i o n c o u l d be achieved using narrowband r a d i a t i o n a t h e 194.2 nm 6p 2P + 6s 2S t r a n s i t i o n , w h i l e s e l e c t i v e l y m i x i n g $he g r o u h s t a t e hyper f ine leve ls w i th appropr ia te mic rowave rad ia t i o n . A f i r s t -o rde r f i e ld i ndependen t m ic rowave c l o c k t r a n s i t i o n , w h i c h i s p a r t i c u l a r l y w e l l s u i t e d t o t h e use o f t h e P e n n i n g i o n t r a p i s t h e 25.9 GHz ( F , M ) = (2 , l ) t-) (1,l) h y p e r f i n e t r a n s i t i o n a t a m i g n e t i c f i e l d o f 0.534 T. The twophoton Dopplerf ree 5d9 6s2 2D5 t-) 5d1° 6s 2S t r a n s i t i o n a t 563 nm i s a p o s s d l e c a n d i d a t e f o b an opt ical f requency standard. Both standards have the po ten t ia l o f ach iev ing abso lu te accurac i e s o f b e t t e r t h a n one p a r t i n 1015 and frequency s t a b i l i t i e s o f l e s s t h a n

Timekeeping potentials using passive hydrogen masers

Abstract: Recent experimental data on the frequency stability of the National Bureau of Standards small passive hydrogen masers indicates that they are superior to any commercially available cesium standard for frequency comparisons or timekeeping out to periods of at least a month. Frequency drift between the small passive hydrogen maser and an ensemble of nine commercial cesium standards has been measured and is of order 1 ± 5 x 10-16/day averaged over 72 days. This is substantially less than the drift in active hydrogen masers. Timekeeping to a few nanoseconds per week has been demonstrated using the small passive hydrogen maser. These small masers are expected to be available in a 30 cm high rack mount in the near future. Using full-sized passive hydrogen masers, it appears possible to achieve frequency stabilities of order 10-15 over days and timekeeping to about one nanosecond per week. In order to take full advantage of the improved capabilities of the passive hydrogen masers, it will be necessary to use improved time comparison techniques.

Laser cooled, stored ion experiments at nbs and possible applications to microwave and optical frequency standards

Abstract: Research on stored ion frequency standards at the United States National Bureau of Standards is brief 1 y discussed. We summarize past work and indicate directions of future research. Introduction. - The purpose of this paper is to briefly summarize the work at the National Bureau of Standards (NBS) which has been directed towards realizing a frequency standard based on stored ions. The similar work of other groups (I) is not discussed here. This summary briefly describes past work and indicates future directions of research at NBS. The stored ion work at NBS was initiated in the Fall of 1977. The goal of this work has been to devise a technique for realizing a frequency standard whose accuracy would be significantly better than that of the Cs atomic beam frequency standard. With this in mind, the ion storage method (2) was pursued because it can provide long confinement times without the usual perturbations associated with confinement (e.g., the wall shift in the H-maser). The initial work was directed toward realizing laser c ooling of ions 131, since this would provide a way to substantially suppress the frequency shift due to the second-order Doppler or time-di lation effect. For these initial experi- ments, Mg+ ions were stored in a Penning trap. Mg+ ions were chosen, since the electronic s tructure is fairly simple (i.e., like that of neutral alkali atoms) and required a laser source at 280 nm. The Penning trap was chosen because the residual h eating mechanisms (at least for a cloud of ions) are l ess than for the

Preliminary Investigation of a New Optically Pumped Atomic Rubidium Standard

Abstract: Mark Feldman, J. C. Bergquis t , L L. Lewis, and F. L. Walls Frequency and Time Standards Group Time and Frequency D i v i s i o n Nat ional Bureau of Standards Boulder. Colorado 80303 Summary We a r e s t u d y i n g t w o t y p e s o f o p t i c a l l y pumped g l a s s c e l l s w h i c h do n o t c o n t a i n a b u f f e r gas and have no w a l l c o a t i n g i n w h i c h b e a m l i k e p r o p e r t i e s a re exp lo i t ed . The f i r s t d e v i c e i s a sealed g lass tube o f abou t 1 cm diameter and 20 cm leng th . A sinal 1 amount o f 87Rb metal i s l o c a l i z e d a t one end by temperature gradients which a lso cont ro l the vapor pressure. The c e l l has t h e p r o p e r t i e s o f a broad atomic beam f o r t h e t r a n s p o r t o f o p t i c a l l y pumped atoms from one nd t o t h e o t h e r with c o l l i m a t i o n g i v e n b y t h e a s p e c t r a t i o o f t h e t u b e . A t each end the Rb "beam" i s crossed by a l ase r . I n each i n t e r a c t i o n r e g i o n , t h e l a s e r o p t i c a l l y pumps atoms i n t o one o f t h e 5 2 S h y p e r f i n e l e v e l s , as we l l as detects populat ion kanges between the h y p e r f i n e l e v e l s . I n a second device, graphi te i n s e r t s a r e i n c l u d e d i n the g lass tube. The g r a p h i t e s t r o n g l y g e t t e r s Rb, the reby p rov id ing c o l l i m a t i o n and s i g n i f i c a n t l y r e d u c i n g s c a t t e r i n g o f l a s e r l i g h t f r o m background Rb atoms. A TE m i c r o w a v e c a v i t y i s p o s i t i o n e d between the w l a s e r i n t e r a c t i o n r e g i o n s . I n t h e b r o a d beam device we have observed the t r a n s p o r t o f o p t i c a l l y pumped atoms between t h e ends w i t h a S/N r a t i o o f 300:l i n 1 S . A tunable dye laser was used f o r t h e pumping and signal d e t e c t i o n . I n t h e c o l l i m a t e d beam device, we have obsewed microwave t rans i t ions us ing a d iode lase r f o r pumping and f luorescence detection.

Design considerations and performance of nbs-6, the nbs primary frequency standard

Abstract: The cons t ruc t ion and performance o f NBS-6, t h e U.S. cesium primary frequency standard, are summarized. A b r i e f d e s c r i p t i o n o f eva lua t ion procedures and sources o f uncer ta in ty are given. In t roduc t ion . The Uni ted States' pr imary frequency standard, NBS-6, was p laced i n t o serv ice i n 1975. The cesium c lock was b u i l t upon the bas ic framework prov ided by NBS-5, b u t var ious improvements o f the device were r a d i c a l enough t o warrant a new standard designation. The basic design uses dipole-magnet s t a t e se lectors , a conventional U-shaped, rectangular cross-sect ion Ramsey c a v i t y , and r e v e r s i b l e mu1 ti channel c o l l imator and hot-wi re detector . For the l a s t several years, annual evaluat ions o f NBS-6 have been made i n order t o prov ide s teer ing in fo rmat ion t o the Nat ional Bureau o f Standards (NBS) embodiment o f atomic time, AT(NBS). The standard has n o t been operated continuous ly as a p a r t i c i p a n t i n the NBS t ime scale. This phi losophy has been supported by recent data g i v i n g the r e l a t i v e performance o f NBS-4 (which i s operated cont i n u o u s l y as p a r t o f the NBS t ime scale); t h e u n o f f i c i a l working t ime scale a t NBS, UTC(8/S); and a small passive hydrogen maser (SPHM). F igure 1 shows the s t a b i l i t y obtained by comparing SPHM w i t h NBS-4 and w i t h UTC(8/S). NBS-4 i s normally a la rge c o n t r i b u t o r t o UTC(8/S). However, much o f t h i s p a r t i c u l a r data was taken when NBS-4 was turned off fo r maintenance. These curves i n d i c a t e no t on ly t h a t the j o i n t s t a b i l i t y o f SPHM vs. NBS-4 i s about 2 x t-' f o r t < l o 5 s, b u t t h a t the long-term s t a b i l i t y o f UTC(8/S) i s about 2 x 10l4 fo r t < l o 6 s. An e f f o r t i s i n progress t o complete a d d i t i o n a l masers t o add t o the NBS t ime scale. When these c locks j o i n t h e scale, i t w i l l become even more unnecessary t o operate a pr imary standard cont inuously. The shortterm and long-term s t a b i l i t y o f NBS-6 were designed t o enable us t o achieve the accuracy l i m i t e d by c a v i t y phase s h i f t i n t h e clock. The accuracy i s l i m i t e d by the degree o f r e t r a c e upon beam reversal , which r e s t r i c t s the l e v e l o f cance l la t ion o f c a v i t y phase s h i f t . The most uncer ta in component o f t h e c a v i t y phase s h i f t i s the d i s t r i b u t e d s h i f t across the microwave c a v i t y windows. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1981829