An alternative cold cesium frequency standard: the continuous fountain

Abstract

Abstract-We report on the primary frequency standard now under construction at the Observatoire de Neuchâtel (ON). The design is based on a continuous fountain of lasercooled cesium atoms, which combines two advantages: the negligible contribution of collisions to the inaccuracy and the absence of stability degradation caused by aliasing effects encountered in pulsed operation. The design is reviewed with special emphasis on the specific features of a continuous fountain, namely the source, the microwave cavity (TE 021 mode), and the microwave modulation scheme. The possible sources of frequency biases and their expected contributions to the error budget are discussed. Based on present data, an accuracy in the low 10 ;15 range and a short-term stability of 7 10 ;14 are attainable simultaneously under the same operating conditions.

Limitation of the frequency stability by local oscillator phase noise: new investigations and natural improvements

“…Similar behavior also may occur for flicker frequency noise, which is naturally observed up to a few Hertz in ultra-stable oscillators. Also, it is over a large Fourier frequency range, the natural behavior of microwave ultrastable oscillators [11] used as local oscillators in high performance atomic beam clocks [12].…”

Design Details of FOCS-2, an Improved Continuous Cesium Fountain Frequency Standard

“…It continues as a joint effort between METAS and the Laboratoire Temps et Fréquence of the University of Neuchâtel (LTF-IMT). The design and construction of the continuous cesium fountain clock FOCS-1 was first described at EFTF1999 [16]. In 2003, this standard was transferred to METAS where its metrological evaluation is still in progress.…”

Continuous beams of cold atoms for space applications

“…c) The continuous fountain [9][10][11] which allows one to reduce simultaneously intermodulation effects and collisional shifts by more than two orders of magnitude. This relaxes, by the same margin, the compromise faced in most pulsed fountains between high stability (but high collisional shift and uncertainty), and high accuracy (but moderate frequency stability), without resorting to a better oscillator than state-ofthe-art, space qualified, quartz oscillators.…”

“…1, together with its main operating characteristics. As described in detail in [9][10][11], the continuous beam is produced from a 3D molasses with three pairs of counter- propagating beams, orthogonal to each other, one horizontal and two at 45…”