小型光抽运铯束频标在不同抽运-检测机制下的光频移

本文对光抽运铯束频标中４种不同的光抽运、光检测机制下的光频移及其对频标频率准确度的影响作了计算。同时还计算了铯炉温度、微波功率及激光功率等因素的变化对光频移引起的频率移动的影响。     

一种小型化铷原子频标腔泡系统及其频移特性

介绍一种新的小型铷频标腔泡系统的结构特点和频移特性。研究了腔牵引效应、微波功率频移、光频移和缓冲气体温度系数对铷频标输出频率的影响。结果表明,上述因素影响都在可以接受的范围内。此腔泡系统体积小、信噪比高、参数优化方便。利用此腔泡系统可以制成小型化、高性能的铷原子频标。     

半导体激光抽运铷频标缓冲气体温度系数的测量方法

为了减小温度对铷频标的影响,通常把具有正、负温度系数的缓冲气体按一定的比例混合,使充入吸收泡的混合气体的温度系数为零。因此,精确测定各种缓冲气体的温度系数十分重要。但是,在铷频标中缓冲气体频移和光频移混在一起,光频移又与谱灯、滤光泡、吸收泡中缓冲气体的温度、气压密切相关,精确测定光频移是非常困难的,这就使精确测定缓冲气体的温度系数变得十分复杂。然而在半导体激光抽运铷频标中,由于半导体激光器是单模的,由它代替谱灯之后不再需要充有缓冲气体的滤光泡,能够比较精确地测定光频移,控制它的大小还可改变半导体激光器的功率和频率,因此,缓冲气体的频移测量就变得简单了。在本文中,我们提出了半导体激光抽运铷频标缓冲气体频移的测量方法,并对铷频标中常用的几种缓冲气体的温度系数进行了测试。     

拉曼光频移对原子干涉测量中原子数的影响

冷原子干涉测量技术在重力加速度测量等领域已经超越传统测量方法,成为量子精密测量的重要发展方向。在干涉测量过程中,由于原子受到重力场影响,速度不断变化,因此激光相对原子具有多普勒频移效应。本文通过对原子跃迁概率及速度选择的理论分析,计算了在拉曼激光脉冲持续时间内,由于多普勒频移造成的原子跃迁概率改变。进而,具体计算了π/2-π-π/2干涉方案中,频移造成的有效原子数损失,及其对干涉条纹对比度产生的影响。     

测量雷达的距离多普勒耦合修正方法研究

线性调频脉冲压缩体制的测量雷达,在探测运动目标时,由于距离-多普勒耦合效应的影响,多普勒频移会使雷达产生测距误差,且该误差与目标径向速度成正比。针对该问题,文章在分析多普勒频移对线性调频脉压影响的基础上,给出了距离多普勒耦合修正方法,并利用雷达实测数据进行了验证,有效提高了测量雷达的测距精度。     

分离型吸收泡^87Rb频标的研制

本文报导了利用分离型吸收泡制成的铷频标中有关光频移、微波功率频移、壁移等问题的实验研究。结果表明,光频移可以减小一个数量级;但由于泡壁石蜡涂层的放气使得微波功率频移不能消除,壁移的温度系数也较大。     

铯原子束频标中Majorana跃迁频移实验

本文介绍根据《铯原子束频标中的Majorana跃迁频移》一文的理论分析结果进行的一些实验。     

基于辐射噪声强度和线谱多普勒的目标运动参数估计

提出了一种利用辐射噪声强度和线谱多普勒频移联合估计匀速直线运动目标的速度和正横距离的方法。该方法基于单水听器观测,首先在球面波近似下利用目标辐射噪声强度估计出正横时刻并确定目标速度和正横距离之间满足的线性关系;然后利用线谱多普勒频移,通过对一个新定义的代价函数进行一维搜索的方法估计出目标速度和正横距离。与现有各种基于噪声强度和线谱多普勒频移进行测距测速的方法相比,该方法具有以下优点：（1）要求更少的先验知识,易于确定参数搜索范围;（2）参数估计过程中仅需一维搜索,并且算法可应用于需对目标参数进行预报的场合。数值仿真给出了不同参数条件下目标运动参数估计结果的统计误差。湖试结果验证了该方法的有效性。     

聚苯乙烯拉曼频移标准物质的研制

拉曼频移常用于揭示物质的组成成分、晶型结构、应力应变等内在信息,因此拉曼频移的校准对拉曼光谱的定性及半定量分析十分重要.研制了聚苯乙烯拉曼频移标准物质,可用于拉曼光谱仪频移的校准,解决不同拉曼光谱仪测试结果缺乏可比性的问题.研制的标准物质经检验,具有良好的均匀性和稳定性.使用可溯源至光谱辐射照度国家基准的激光共聚焦拉曼...     

基于密集频谱校正的电流信号高准确度分离技术

为实现具有密集频谱的频谱校正分离,通过研究基于复调制移频和低通滤波器的传统Zoom-FFT方法和频谱校正方法,提出一种电流信号高准确度分离方法。该方法采用基于复解析带通滤波器和复调制移频的频谱细化方法和比值校正法对电流信号进行频谱细化校正,实现电流信号的高准确度分离。研究结果表明,该文采用的频谱细化校正方法运算量小,计算速度快、准确度高,能够实现电流信号的高准确度分离。     

Power dependence of the frequency bias caused by spurious components in the microwave spectrum in atomic fountains

The presence of spurious spectral components in the microwave excitation may induce frequency shifts in an atomic fountain frequency standard. We discuss how such shifts behave as a function of power variations of the excitation carrier and in the spur-to-carrier ratio. The discussion here is limited to the case of single-sideband spurs, which are generally much more troublesome due to their ability to cause frequency shifts. We find an extremely rich and unintuitive behavior of these frequency shifts. We also discuss how pulsed operation, typical of today's fountain frequency standards, relates to frequency shifts caused by spurs in the microwave spectrum. The conclusion of these investigations is that it is, at best, difficult to use elevated power microwaves in fountain frequency standards to test for the presence of spurs in the microwave spectrum.     

Light shifts in an optically pumped Cs beam frequency standard

Frequency shifts caused by light, which are called light shifts in an optically pumped Cs beam frequency standard, were estimated. Frequency shifts due to monolithic light were measured by introducing laser light along the Cs beam. The relative dependence of the shift on the laser frequency agreed very well with the theory, but the absolute shift was between one and two times that of the theory. The light shifts due to the optical pumping and optical detection in the standard are estimated to be less than 2×10^-15 and 1×10^-16, respectively, and both are negligible at the present state of development     

Light and Buffer-Gas Frequency Shifts in the 85Rb-Maser Frequency Standard

Recently we reported the operation of an optically pumped 85Rb maser oscillating at 3.035734 GHz on the field-independent transition 52S1/2(F = 3, mF = 0 ? F = 2, mF = 0) [1]. Apart from cavity pulling, the two major sources of frequency shifts are those due to the buffer gas and the pumping light. The short-term phase stability of the standard is not appreciably affected by these shifts. The buffer-gas shift can be used to advantage to select an output frequency that is different from the ground-state hyperfine frequency.     

On-line recalibration of spectral measurements using metabolite injections and dynamic orthogonal projection

Spectrometers are enjoying increasing popularity in bioprocess monitoring due to their non-invasiveness and in situ sterilizability. Their on-line applicability and high measurement frequency create an interesting opportunity for process control and optimization tasks. However, building and maintaining a robust calibration model for the on-line estimation of key variables of interest (e.g., concentrations of selected metabolites) is time consuming and costly. One of the main drawbacks of using infrared (IR) spectrometers on-line is that IR spectra are compromised by both long-term drifts and short-term sudden shifts due to instrumental effects or process shifts that might be unseen during calibration. The effect of instrumental drifts can normally be reduced by referencing the measurements against a background solution, but this option is difficult to implement for single-beam instruments due to sterility issues. In this work, in order to maintain the robustness of calibration models for single-beam IR and to increase resistance to process and instrumental drifts, planned spikes of small amounts of analytes were injected periodically into the monitored medium. The corresponding measured difference spectra were scaled-up and used as reference measurements for updating the calibration model in real time based on dynamic orthogonal projection (DOP). Applying this technique led to a noticeable decrease in the standard error of prediction of metabolite concentrations monitored during an anaerobic fermentation of the yeast Saccharomyces cerevisiae.     

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.     

A beam reversal experiment for the estimation of microwave powershifts in an optically pumped Cs beam frequency standard

The characteristics of microwave-power-dependent frequency shifts of an optically pumped Cs frequency standard are reported. The general features of the shifts are in good agreement with simple theoretical predictions. The shift is quite symmetrical in beam reversal, and the standard deviation of the difference between the observed and predicted shift is about 6×10-14     

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.     

Bending mode effect on sensitivity of plate surface acoustic wave pressure sensors

The bending mode effect on sensitivity of pressure sensors operating with surface acoustic waves (SAW) propagating over the surface of a plate is analyzed using Tiersten's perturbation integral for frequency shifts in a piezoelectric resonator due to the presence of initial fields. For a plate subjected to nonpure bending, the SAW speed, whose shift in response to pressure determines the sensitivity, can be defined locally through the local variations of the effective material constants. Three common bending modes of pure bending, bending under a concentrate load, and bending under a uniformly load are analyzed and compared.     

Frequency shifts in cesium beam clocks induced by microwave leakages

The anomalous sensitivity of an optically pumped cesium beam clock to microwave power and the unexpected frequency shifts observed are demonstrated to result from microwave leakages outside the arms of the Ramsey cavity. A new design of the cavity associated with a careful realisation provides very weak microwave leakages and negligible related frequency offsets. We have established a theoretical model that allows us to calculate the frequency shifts due to microwave field components propagating along the beam axis in regions which are free-field in an ideal Ramsey cavity. This results in first order Doppler effect shifts. The order of magnitude of the frequency shift can be predicted and agrees with the measured one when the amplitude of the leakage magnetic field is about a 1000 times smaller than the amplitude of the microwave interrogation field in the cavity.     

轻质弱辐射的阻尼夹芯复合材料圆柱壳的优化设计

基于三维弹性理论,对阻尼夹芯复合材料圆柱壳在简谐点力作用下的振动声辐射进行优化研究。建立了以总质量、基频和模态阻尼为优化目标的多目标函数优化模型,对纤维层和芯层厚度分布和铺层方式进行优化设计;经与其他文献及"有限元+边界元"法得到的结果对比,验证了三维弹性理论的计算结果的有效性;分析了三明治夹芯圆柱壳的振动和声辐射的影响因素,发现芯层中面线位置高于整壳中面线时有利于提高基频,降低声辐射功率;且随着铺层角的增加,固有频率呈抛物线型变化趋势,模态阻尼比则逐渐减小。经优化设计,声功率一阶共振频率向高频方向偏移20 Hz,最大声功率降低11.66 dB,200 Hz以下的低频段,声功率峰值密度明显降低。