守时型铯原子喷泉钟关键技术的研究和实现

发布时间：2018-06-13 14:37

本文选题：外腔半导体激光器 + 液晶相位延迟器　；参考：《中国科学院研究生院(国家授时中心)》2012年博士论文

【摘要】：时间频率是一个国家科技、经济、军事和社会生活中至关重要的参量，其应用范围从基础研究（相对论验证、基本物理常数测量等），渗透到了工程技术应用领域（导航定位、深空探测等）。标准时间首先由一组连续运行的守时型原子钟（如商品型铯束原子钟、氢原子钟）产生稳定的信号，经过基准型原子钟（如铯原子喷泉钟、实验室型铯束原子钟）校准后获得稳定、准确的时间信号。铯原子喷泉钟作为基准钟标较着其他原子钟，具有最高的准确度性能和优异的长期稳定度性能。相比于现有的守时原子钟，铯原子喷泉钟不存在氢钟所固有的频率漂移，比商品型铯束原子钟具有更高的频率稳定度（1个量级以上），参与守时能够显著提高时间频率信号的长期稳定度性能。然而，铯原子喷泉钟作为守时钟运行仍然需要解决以下两个关键问题：一是铯原子喷泉钟的可靠性问题。目前作为基准钟运行的铯原子喷泉运行是间歇性的，而作为守时钟运行则要求输出信号是连续的，以保证时间信号的持续性。铯原子喷泉钟是大型的实验室装置，各种环境因素（机械振动等）的干扰容易导致喷泉钟偏离正常的工作状态，研究能够自动恢复工作状态的技术能够是其中需要研究的关键技术之一；二是需要解决铯原子喷泉准确度和稳定度性能相互矛盾的问题。铯原子喷泉钟作为守时钟运行在保证高准确度的同时也必须具有高的稳定度性能。当喷泉钟原子样品数目越小时，原子样品之间的碰撞程度减弱，导致的碰撞频移误差减小，如此一来稳定度性能指标就响应地降低。研究能够同时提高准确度性能和稳定度性能的技术是另一项需要研究的关键技术。本文围绕上述问题开展研究，首先研制了具有抗振特性的外腔半导体激光器，在此基础上，研究了具有参数自恢复激光稳频技术，解决了限制铯原子喷泉钟连续运行能力的主要问题；研究了能够获得低密度原子样品同时又能保证原子团数目不变的慢速原子束技术，可同时提高铯喷泉钟准确度和稳定度性能指标。在实现的关键技术基础上，研制了铯原子喷泉钟的其中两个子系统物理系统、光学系统，通过整机联调，获得了铯原子喷泉钟的标志性Ramsey信号，实现了初步闭环，研究内容和成果可归纳为以下几个部分：（1）研制了应用干涉滤光片选模，具有“猫眼”结构和参数自恢复锁频功能的新型852nm抗振外腔半导体激光器系统，并成功应用于铯原子喷泉钟装置。分析研究了基于干涉滤光片选模、“猫眼”结构外腔压窄线宽的外腔激光器的工作原理，与基于光栅选模、FP腔压窄线宽的外腔激光器对比，分析了研制的外腔半导体激光器的抗振特性。测试了抗振外腔半导体激光器的频谱特性，与同类的外腔半导体激光器相比，研制的激光器具有更窄的线宽和更高的频谱纯度。（2）首次实现了基于液晶相位可变延迟器频率调谐、“猫眼”结构外腔的半导体激光器，提出了基于半导体光放大芯片新型外腔半导体激光器方案。针对PZT频率调谐的外腔半导体激光器固有的回程误差、机械运动和驱动电压高等缺点，采用了以液晶相位延时器进行调谐的方案。在此基础上，实现了液晶调谐的外腔半导体激光器。测试表明，研制的激光器具有调谐电压低，不存在回程误差和机械运动等优点。（3）研究了2D MOT慢速原子束技术。通过构建了2D MOT中铯原子的受力模型，对2D MOT产生慢速原子束的过程进行了数值模拟。利用模拟结果，设计并实现了完整的慢速原子束装置，利用飞行时间法测试了慢速原子束的流量、平均速度等特性，获得了性能指标较好的慢速原子束。采用慢速原子束直接通过光学粘团制备原子样品，可以缩短装载时间，降低原子团密度，同时提高频率稳定度性能和准确度性能。（4）研制了铯原子喷泉钟的物理系统和光学系统，，通过整机联调，成功地获得了铯原子喷泉钟的标志性信号---Ramsey条纹，并初步实现了喷泉钟的闭环运行。在研制的抗振外腔半导体激光器的基础上，通过饱和吸收光谱，实现了激光器的自动稳频，并利用声光调制器实现了激光频率、功率控制，通过光放大、注入锁定方法实现光功率放大。通过保偏光纤把激光传输到一体化镜筒，扩束形成准直度高、功率和偏振可调的圆偏振光。构建了斜入射激光探测光路，减小了热原子荧光的干扰。全面分析了铯原子喷泉钟对物理的要求，对物理系统进行了方案设计。依据设计方案，实现了铯原子喷泉钟的MOT阱区、探测区、喷泉管，达到了喷泉钟运行所需的指标。在铯原子喷泉钟光学系统、物理系统完成的基础上，通过整机联调，实现了铯原子的多普勒冷却、上抛、偏振梯度冷却，实现了原子喷泉。利用选态腔和推斥光，实现了mF=0态原子的选择。通过在微波腔馈入微波，获得了铯原子喷泉钟的标志性的Ramsey谐振信号。通过对微波信号实施方波调制，获得了本地振荡器的伺服控制信号，实现了喷泉钟的初步闭环。
[Abstract]:Time and frequency is a vital parameter in a country's scientific, economic, military and social life. Its application ranges from basic research (relativistic verification, basic physical constant measurement, etc.) to the application field of Engineering (navigation and positioning, deep space exploration, etc.). The standard time is first run by a group of continuous time conservative atomic clocks (such as quotient). The caesium atomic clocks, hydrogen atomic clocks produce stable signals. After calibrating the standard atomic clocks (such as cesium fountain clocks, laboratory caesium beam atomic clocks), the stable and accurate time signals are obtained. The cesium fountain clock has the highest accuracy performance and excellent long-term stability performance as the reference clock is compared with the other atomic clocks. Compared with the existing time-saving atomic clocks, the cesium fountain clock does not have the frequency drift inherent to the hydrogen clock, which has a higher frequency stability than the commercial cesium beam atomic clock (1 orders of magnitude), and the time and frequency signal can significantly improve the long-term stability performance of the time frequency signal.
However, the cesium fountain clock still needs to solve the following two key problems: first, the reliability of the cesium fountain clock. The current operation of the cesium fountain as the reference clock is intermittent, and the output signal is continuous as a clock keeping operation in order to ensure the continuity of the time signal. The sub fountain clock is a large laboratory device. The interference of various environmental factors (mechanical vibration, etc.) may cause the fountain clock to deviate from the normal working state. It is one of the key technologies to study the technology that can automatically restore the working state. Two it is necessary to solve the mutual spear of the accuracy and stability of the cesium fountain. The caesium atomic fountain clock, as a clock guard, must have high accuracy as well as high stability. When the number of atomic clocks is smaller, the degree of collisions between the atomic samples decreases and the collision frequency shift error decreases. At the same time, improving the accuracy and stability performance is another key technology that needs to be studied.
In this paper, an external cavity semiconductor laser with anti vibration characteristics is first developed. On this basis, the parameter self recovery laser frequency stabilization technology is studied, and the main problem to restrict the continuous operation of cesium fountain clock is solved, and the low density atomic sample can be obtained and the atom can be guaranteed at the same time. The low speed atomic beam technique can simultaneously improve the accuracy and stability of the cesium fountain clock. On the basis of the key technology realized, two subsystems of the cesium fountain clock are developed, and the optical system is used to obtain the symbolic Ramsey signal of the cesium fountain clock. The research contents and achievements can be summarized as follows:
(1) a new type of 852nm anti vibration external cavity semiconductor laser system with "cat's eye" structure and self recovery of parameters has been developed, and it has been successfully applied to the cesium fountain clock device. The working origin of the external cavity laser based on interference filter selection mode and the narrow line width of the outer cavity of the cat eye structure is analyzed and studied. Compared with the external cavity laser based on the grating selection and the narrow line width of the FP cavity, the anti vibration characteristics of the developed external cavity semiconductor laser are analyzed. The spectrum characteristics of the anti vibration external cavity semiconductor laser are tested. Compared with the same kind of external cavity semiconductor laser, the laser apparatus has a narrower line width and higher spectral purity.
(2) a semiconductor laser based on the frequency tuning of the liquid crystal phase variable retarder and the outer cavity of the cat's eye is first realized. A novel external cavity semiconductor laser based on the semiconductor optical amplifier chip is proposed. The shortcomings of the inherent back range error of the PZT frequency tuning external cavity semiconductor laser, the high mechanical motion and the high driving voltage are adopted. On the basis of this, the liquid crystal tunable external cavity semiconductor laser is realized. The test shows that the laser has the advantages of low tuning voltage, no return error and mechanical motion.
(3) the 2D MOT slow atomic beam technique is studied. Through the construction of the force model of the cesium atom in 2D MOT, the process of the slow atomic beam produced by 2D MOT is simulated. The complete slow atomic beam device is designed and realized by the simulation results. The flow of the slow atomic beam and the average velocity are measured by the time of flight method. The slow atomic beam with good performance index is obtained. Using the slow atomic beam to prepare the atomic sample directly through the optical visco, it can shorten the loading time, reduce the density of the atomic mass, and improve the performance and accuracy of the frequency stability.
(4) the physical and optical systems of the cesium fountain clock have been developed. The ---Ramsey stripe of the caesium atomic fountain clock is successfully obtained through the adjustment of the whole machine, and the closed loop operation of the fountain clock is preliminarily realized. On the basis of the developed anti vibration external cavity semiconductor laser, the laser is realized by the saturated absorption spectrum. The laser frequency and power control are realized by the acousto-optic modulator. The optical power amplification is realized by the optical amplification and injection locking. The laser is transmitted to the integrated lens by the polarization maintaining fiber and the beam is expanded to form the circular polarized light with high collimation, power and polarization adjustable. The laser detection path of oblique incidence is constructed and the thermal atomic fluorescence is reduced. The requirements of the caesium fountain clock for physics are comprehensively analyzed and the physical system is designed. According to the design scheme, the MOT well area of the cesium fountain clock, the detection area and the fountain tube have been realized, and the requirements for the fountain clock operation are achieved. On the basis of the cesium atomic fountain clock optical system and the physical system completion, the whole machine is completed. In combination, the atomic fountain is realized by the Doppler cooling, throwing, and polarization gradient cooling of the cesium atom. The selection of the mF=0 state atom is realized by using the selected state cavity and the repulsion light. By feeding the microwave in the microwave cavity, the Ramsey resonant signal of the cesium fountain clock is obtained. The local wave modulation of the microwave signal is obtained. The servo control signal of the oscillator realizes the preliminary closed loop of the fountain clock.
【学位授予单位】：中国科学院研究生院(国家授时中心)
【学位级别】：博士
【学位授予年份】：2012
【分类号】：P127.12

【引证文献】