一种极小型氢频标

上海天文台正在研制一种守时用极小型氢原子钟。该频标采用了一个精密的电容式负载谐振腔,它的体积小,从而使标频的体积和重量较通常的氢原子钟大大减小。精密腔的Q值采用正反馈获得增益,从而能维持脉泽振荡并改善信号的信噪比。由于采用了腔自动调谐系统,该频标的长期稳定性可与通常氢钟相比,甚至更好。目前,该频标已建立起来,获得了脉泽振荡信号并锁定晶振,且腔自动调谐系统工作灵敏。     

守时用小型氦原子钟的研制

本文报告了一种守时用小型氢原子钟的设计和研制，该钟应用了一个精密的电容式谐振腔，由于其体积很小，从而使钟的整体体积和重量较通常的氢钟大大减小，腔的Q值采用正反馈得增益，从而维持氢脉泽振荡并改善信号的信噪比，由于采用了腔频自动调谐,钟的长期稳定度可与通常的氢钟相比。     

守时用小型氢原子钟的研制

本文报告了一种守时用小型氢原子钟的设计和研制。该钟应用了一个精密的电容式谐振腔，由于其体积很小，从而使钟的整体体积和重量较通常的氢钟大大减小。腔的Ｑ值采用正反馈获得增益，从而能维持氢脉泽振荡并改善信号的信噪比。由于采用了腔频自动调谐系统，钟的长期稳定度可与通常的氢钟相比。     

腔体自动调谐氢脉泽的研究

氢脉泽是迄今为止除极短时间测量间隔之外最稳定的频率标准 ,但对于 1 0 4秒或更长的测量时间间隔 ,它的性能由于高Q值谐振腔而引起频率漂移而变坏。由于环境温度的变化及谐振腔老化而引起谐振腔频率的变化 ,导致氢脉泽长期频率稳定度的降低。为了减小这种影响需借助一种自动调谐器来确保谐振腔的频率始终工作在所需的频率上 ,以改善氢脉泽的长期频率稳定度 ,其日稳定度可达 1 0×1 0 - 1 4 。本文描述了上海天文台研制的带有腔体自动调谐的氢脉泽的性能     

氢脉泽振荡参数q的实验估算及氢脉泽诊断技术

本文介绍一种实验估算氢脉泽振荡参数q的测量方法。指出氢脉泽“基线数据”测量的重要性在于最终可用来进行氢脉泽的诊断。     

主动型氢脉泽物理系统的小型化

为实现主动型氢原子钟脉泽的小型化,对其物理结构进行了优化设计。其中,腔-泡结构、真空系统、C场线圈、束光学系统、磁屏蔽系统均被理论分析和优化设计,并进行了相关的验证实验。双真空结构设计有效地减小了氢脉泽的尺寸。在此基础上,对空间应用主动型氢原子钟的地面样机进行了研制,复合泵技术进一步减小了主动型氢原子钟的尺寸和重量。     

流动VLBI站氢原子钟的研制与性能测试

氢脉泽是至今为止除极短时间测量间隔之外最稳定的频率标准 ,它是射电天文所必需的频率标准。本文讨论了为流动VLBI站研制的新一代氢脉泽的物理结构特点 ,包括对腔泡结构、磁屏蔽、原子束光学系统等采用的新技术。性能测试表明 ,在 80s到 1d之间其频率稳定度优于 1× 10 - 1 4 ,有了较大的提高。     

新氢脉泽频标的电子学支持系统

氢脉泽的电子学支持系统是氢脉泽频标中的一个重要组成部分,它包括有脉泽的热控制、磁场控制、氢压以及调谐控制。本文介绍上海天文台的新氢脉泽频标电子学支持系统各个控制部分的设计思想及特点。     

双真空主动型氢脉泽真空系统设计

清洁、抽速稳定的高真空系统是氢脉泽工作必不可少的组成部分之一。文章详细介绍了双真空主动型氢脉泽真空系统的组成及各个组成部分的设计思路、方法。内容涉及真空的获得、真空泵的选择、氢脉泽物理部分双真空系统设计、流导及抽速的计算、泵体结构的设计和实验验证。实验发现,设计完毕的氢脉泽双真空系统保温效果较以前大幅改善,内外真空室本底流量为0.1 mA,工作流量值稳定在0.7mA时氢脉泽稳定输出-105 dBm信号,关闭流量后内真空抽真空本底时间约为8 min。表明内外真空室离子泵均达预期设计指标且工作正常。此外,该设计还进一步减小了脉泽体积、减轻了其重量,向氢脉泽小型化迈出了坚实一步。     

改善氢脉泽标准频率稳定度和工作可靠性所采用的技术

本文描述上海天文台为改善氢脉泽标准的频率稳定度和工作可靠性所采用的主要技术,同时给出了采用这些技术后氢脉泽的新的性能数据。     

An experimental study for the compact hydrogen maser with a TE111 septum cavity

We have made experiments on our compact active hydrogen maser with the cylindrical TE111-mode septum cavity, which is almost one-half the conventional TE011-mode cavity in size. An inductive radiation signal was observed, but the maser did not produce self-oscillation. The system supports oscillation when the cavity is placed in an external feedback loop.     

蓝宝石主动型氢原子频标

研制了采用蓝宝石加载微波腔的蓝宝石主动型氢原子频标,腔体外径18 cm,高度20 cm,重量约2.5 kg。由于微波腔体积的减小,整钟体积较传统大氢钟明显减小。经中国计量科学研究院测试,该蓝宝石主动型氢原子频标的技术指标为3.0×10-13@1 s、3.8×10-15@1 d,是目前国内体积最小的高指标、高可靠主动型氢原子频标,可在实验室、车载等环境下使用。     

Studies of dielectrically loaded cavities for small size hydrogenmasers

A dielectrically loaded cavity made of a hollow alumina cylinder, which is used to reduce hydrogen maser size, is considered. The results of a theoretical study of the effect of the cavity geometry on the frequency stability capability of the maser are reported. The active mode as well as the passive mode of operation are considered and the achievable performances are compared. It is shown that the frequency stability capabilities do not differ very much for both modes of operation with, however, a slight advantage to the active mode     

Designs of a microwave TE011 mode cavity for a space borne H-maser.

Method of Lines and Finite Element Analysis investigations have been performed to optimize parameters in a TE011 mode cavity resonator suitable for a spaceborne hydrogen maser. We report on designs that were explored to find a global maximum in the important design parameters for the microwave cavity used in a hydrogen maser. The criteria sought in this exercise were both the minimization of the total volume of the cavity and the maximization of the product of the z-component of the magnetic energy filling factor and the cavity TE011 mode Q-factor (Q.eta). Different configurations were studied. They were a sapphire tube in a copper cylinder, a sapphire tube in a copper cylinder with Bragg reflectors, and spherical copper cavities both empty and sapphire-lined on the inside cavity surface. At 320 K, the simulations resulted in an optimum product Q.eta = 4.9 x 10(4), with an inner cavity radius of 80 mm and unity aspect ratio. This represents a 54% improvement over an earlier design. The expected increase in the product Q . eta) with the inclusion of Bragg reflectors to the sapphire tube was not achieved. Moreover, the z-component of the magnetic energy filling factor was greatly reduced due to an increase in the radial magnetic field. The sapphire-lined spherical cavity showed no better performance than an equivalent-sized empty copper spherical cavity. For the empty cavity the simulations resulted in the product Q.eta = 4.4 x 10(4). The empty spherical cavity resonator is not suitable for the spaceborne hydrogen maser as the total volume in this case is 33% larger than that of the optimized sapphire tube resonator.     

Designs of a microwave TE/sub 011/ mode cavity for a space borne H-maser

Method of lines and finite element analysis investigations have been performed to optimize parameters in a TE/sub 011/ mode cavity resonator suitable for a spaceborne hydrogen maser. We report on designs that were explored to find a global maximum in the important design parameters for the microwave cavity used in a hydrogen maser. The criteria sought in this exercise were both the minimization of the total volume of the cavity and the maximization of the product of the z-component of the magnetic energy filling factor and the cavity TE/sub 011/ mode Q-factor (Q/spl middot//spl eta/). Different configurations were studied. They were a sapphire tube in a copper cylinder, a sapphire tube in a copper cylinder with Bragg reflectors, and spherical copper cavities both empty and sapphire-lined on the inside cavity surface. At 320 K, the simulations resulted in an optimum product Q/spl middot//spl eta/ = 4.9 /spl times/ 10/sup 4/, with an inner cavity radius of 80 mm and unity aspect ratio. This represents a 54% improvement over an earlier design. The expected increase in the product Q/spl middot//spl eta/ with the inclusion of Bragg reflectors to the sapphire tube was not achieved. Moreover, the z-component of the magnetic energy filling factor was greatly reduced due to an increase in the radial magnetic field. The sapphire-lined spherical cavity showed no better performance than an equivalent-sized empty copper spherical cavity. For the empty cavity the simulations resulted in the product Q/spl middot//spl eta/ = 4.4 /spl times/ 10/sup 4/. The empty spherical cavity resonator is not suitable for the spaceborne hydrogen maser as the total volume in this case is 33% larger than that of the optimized sapphire tube resonator.     

Original studies on quantum coherence

The earliest works that demonstrated quantum coherence of masers and lasers are described. Phase coherence of the maser was studied by heterodyning outputs of two independent masers in 1955, and that of lasers in 1963. We also studied coherent superposition of two eigenstates by observing the induced dipole moment of ammonia in the downstream of the maser, oscillating at the frequency of the maser.     

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.     

Experimental Study of the Frequency Stability of a Maser Oscillator Operated with an External Feedback Loop

In this paper, we report the results of an experimental study of the short-and mid-term frequency stability for both a hydrogen maser and a rubidium maser operated with an external feedback loop to modify the cavity quality factor. A revised version of the theoretical expression of the frequency stability for this type of maser is given and a numerical solution for various maser parameters is calculated. The predicted frequency stability exhibits an optimum when the cavity Q is varied. The experimental results presented in this study agree with this conclusion.     

Measurement of the Effect of Thermal Noise on the Amplitude of Oscillation of a Maser Oscillator

Experimental verification of the effect of thermal noise on the oscillation amplitude of a maser is described. Two different masers are considered, the H maser with an homogeneous atomic line and the Rb maser with an inhomogeneous line. The effect is characterized by the spectral density of the relative amplitude fluctuations and this parameter is measured with a conventional superheterodyne AM receiver for various maser saturation factors. Experimental results show good agreement with theoretical predicted values. At high saturation factors, a peak appears with a maximum at a frequency close to the Rabi frequency. Observed values at high Fourier frequencies allow a measurement of the atomic power by the knowledge of the absolute temperature of the cavity and the prediction of the oscillator short-term frequency stability. Furthermore, the effect on amplitude and on frequency noise of an external feedback loop used to increase the cavity quality factor is discussed.