Apparent power-dependent frequency shift due to collisions in a cesium fountain

We describe a situation where a varying collisional frequency shift in cesium fountain primary frequency standards can be misinterpreted as a power-dependent shift. This misinterpretation may affect analyses of fountains test-operated at multiple pi/2 microwave pulse areas. Such tests are typically performed in the search for microwave- and cavity-related systematic frequency biases.     

An alternative cold cesium frequency standard: the continuous fountain

We report on the primary frequency standard now under construction at the Observatoire de Neuchatel (ON). The design is based on a continuous fountain of laser-cooled 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.     

To simulate blackbody radiation frequency shift in cesium fountain frequency standard with CO2 laser.

An experimental scheme to simulate the Blackbody radiation (BBR) frequency shift with carbon dioxide (CO2) laser in cesium fountain frequency standard is proposed. The alternative (ac) electric field from a CO2 laser with 10.6 microm wavelength causes the similar ac Stark shift of the clock transition frequency, but with much higher intensity than BBR power intensity at about room temperature. This scheme provides a simple, new method for measuring the BBR frequency shift in fountain clock. It provides the possibility to explain the difference of BBR shifts in Cs fountain clocks between two measurement methods.     

To simulate blackbody radiation frequency shift in cesium fountain frequency standard with CO/sub 2/ laser

An experimental scheme to simulate the blackbody radiation (BBR) frequency shift with carbon dioxide (CO/sub 2/) laser in cesium fountain frequency standard is proposed. The alternative (ac) electric field from a CO/sub 2/ laser with 10.6 /spl mu/m wavelength causes the similar ac Stark shift of the clock transition frequency, but with much higher intensity than BBR power intensity at about room temperature. This scheme provides a simple, new method for measuring the BBR frequency shift in fountain clock. It provides the possibility to explain the difference of BBR shifts in Cs fountain clocks between two measurement methods.     

Research in creating a fountain type frequency standard

Results of research aimed at creating a new generation of quantum frequency standards, i.e., a cesium fountain, are presented. Measurement data for controlling and detecting cold atoms are analyzed. The possibility of cooling cesium atoms to a level of the order of 2 µK is demonstrated by experiment.Translated from Izmeritelnaya Tekhnika, No. 1, pp. 18–23, January, 2005.     

Development of a cesium atomic fountain frequency standard

We report on the development of a cesium atomic fountain frequency standard at the Korea Research Institute of Standards and Science (KRISS). Cesium atoms were launched upwards by using an optical moving molasses method after they were cooled in a magnetooptical trap. The temperature of launched atoms was about 2.5 /spl mu/K. From our cesium atomic fountain, we were able to observe Ramsey fringes of 1 Hz linewidth on the 9.2 GHz clock transition of cesium atoms.     

A new calculation of the ion velocity shift in a vortex resonance experiment in He II

We calculate the shift in velocity of an ion trapped on a vortex, line in He II when, in addition to a dc electric field directed along the line, an ac field is applied perpendicular to the line. We employ a model of the ion on a line first introduced by Ohmi and Usui and used by them to calculate the dc mobility. The ion drift velocity in the presence of the ac field exhibits a nearly flat plateau as a function of dc field and a canted dip as a function of frequency. The present calculation differs in some details from the earlier one and permits a more reliable estimate of the change in velocity.This work is supported in part by two grants from the National Science Foundation: DMR 72-03221 A01 and GH-34890.     

Characterization of light shift below 10(-15) in a cesium fountain frequency standard operated without the use of mechanical shutters.

We characterize the light shift in the interaction region of a laser-cooled frequency standard and demonstrate an approach for its mitigation without the use of mechanical shutters. The light shift is confirmed to be below 10-15 and expected to be orders of magnitude lower. This technique makes use of a master-slave laser configuration where cutting the injection power to a slave laser causes it to lase at its free-running wavelength, often two or more nanometers off from the atomic resonance.     

Characterization of light shift below 10/sup -15/ in a cesium fountain frequency standard operated without the use of mechanical shutters

We characterize the light shift in the interaction region of a laser-cooled frequency standard and demonstrate an approach for its mitigation without the use of mechanical shutters. The light shift is confirmed to be below 10/sup -15/ and expected to be orders of magnitude lower. This technique makes use of a master-slave laser configuration where cutting the injection power to a slave laser causes it to lase at its free-running wavelength, often two or more nanometers off from the atomic resonance.     

Power dependence of distributed cavity phase-induced frequency biases in atomic fountain frequency standards

We discuss the implications of using high-power microwave tests in a fountain frequency standard to measure the frequency bias resulting from distributed cavity-phase shifts. We develop a theory which shows that the frequency bias from distributed cavity phase depends on the amplitude of the microwave field within the cavity. The dependence leads to the conclusion that the frequency bias associated with the distributed cavity phase is typically both misestimated and counted twice within the error budget of fountain frequency standards.     

变速旋转机械的锁相倍频测试技术

本文介绍了基于虚拟仪器技术的变速旋转机械的锁相倍频测试技术,用硬件方式剔除了测试过程中机械转速不恒定对信号分析的影响,提高了故障诊断的准确性。     

Cs frequency synthesis: a new approach

The paper describes a new approach to synthesizing the Cs hyperfine frequency of 9.192 GHz that is designed to be sufficiently rugged for use in space, specifically for the Primary Atomic Reference Clock in Space (PARCS) planned for the International Space Station, as well as ground applications. This new approach requires no narrow band filters or frequency multiplication, and the primary source of cooling is conduction. Instead of frequency multiplication, it uses a custom regenerative divider stage followed by two commercial binary dividers and several mixing stages. A fractional frequency step of 2x10(-17) is achieved by mixing the output of a 48-bit numerically controlled oscillator with the microwave signal. Preliminary tests on the new synthesizer design indicate an internal fractional frequency stability of 1x10(-15) at 10 s and 1x10 (-18) at 1 d, dominated by the daily room temperature variations. The phase and amplitude noise are similar to our previous designs that used frequency multiplication and narrow band filters. The temperature coefficient is less than 0.2 ps/K.     

套筒连接结构非线性对梁频漂的影响

针对航天器地面振动试验中的频率漂移问题,研究以一端夹支另一端带套筒连接结构均布载荷驱动下的梁为对象,分析了连接结构的轴向回复力、面内摩擦力、预紧力、面内摩擦系数、间隙等非线性因素对梁基频漂移的影响。讨论间隙非线性时,利用相对振型转换法对梁结构进行处理,研究了有、无预紧力两种情况下系统的幅频响应,确定了上述几种因素对梁受迫振动基频的影响,得到的结论对于研究航天器地面振动试验中的频率漂移现象具有参考价值。     

江苏亲亲集团新建万吨冷库用挤塑板整体保温新工艺——冷库整体保温工艺介绍

扬州亲亲集团在新建的万吨冷库中,对于冷库整体保温系统选择,集团领导经过多轮选择,从目前冷库围护结构最流行的现场喷涂聚氨酯改为选择欧文斯科宁公司的挤塑板整体保温系统,本文结合工程板柱剪力墙结构体系的特点就系统的选择及保温系统施工要点等作简要阐述。尤其结合工程剪力墙处保温处理,及使用挤塑板材料,在现场干操作,具有清洁,快速,安全的优点,又保证保温厚度等质量要求,从而避免现场喷涂聚氨酯易造成火灾等事故及环境污染等不利因素。     

First performance results of PTB's atomic caesium fountain and a study of contributions to its frequency instability

At the Physikalisch-Technische Bundesanstalt (PTB), an atomic caesium fountain was constructed. Ramsey fringes with a full width at half maximum (FWHM) of 0.86 Hz were obtained by launching the atoms to a height of 83 cm above the cooling region (40 cm above the microwave cavity center). A first measurement of the homogeneity of the magnetic flux density yields 0.33 nT (rms), only 0.16% of the mean value of 0.205 muT used in normal operation. The inherent elementary noise contributions of the fountain and of a thermal beam atomic clock are compared in some detail.     

Modeling the dependence of the coefficient of restitution on the impact velocity in elasto-plastic collisions

We discuss the modeling of the coefficient of restitution as a function of the incoming velocity in elasto-plastic collisions with normal frictionless impact, and compare the results from nonlinear finite-element analysis to those of two recent normal force displacement models: One by Thornton (ASME J. Appl. Mech. 64 (1997) 383) and one by Vu-Quoc and Zhang (Proc. R. Soc. London, Ser. A 455 (1999) 4013) which is the displacement-driven counterpart of the force-driven model proposed by Vu-Quoc, Zhang, and Lesburg (ASME. J. Appl. Mech. 67 (2000) 363). The resulting values of the coefficient of restitution are also compared to those from the model proposed in Stronge (in: R.C. Batra, A.K. Mal, G.P. MacSithigh (Eds.), Impact Waves and Fractures, ASME AMD 205 (1995) 351). The relationships among the coefficient of restitution, the incoming velocity, the collision time, the contact force/displacement, the normal pressure distribution are presented and discussed. These results establish the better accuracy provided by the model proposed by Vu-Quoc, Zhang, and Lesburg, when compared to previously proposed models.     

Light shift compensation in a Rb gas cell frequency standard withtwo-laser pumping

One of the most important physical processes occurring in Rb frequency standards is the light shift, which depends strongly on the intensity and the optical frequency detuning of the pumping light. This paper presents a method to compensate the light shift by means of two-laser pumping. The two-laser pumping schemes will also improve the signal-to-noise ratio, because almost all atoms can be pumped to the desired state