铯原子喷泉钟NTSC-01光学系统的研制

【作者】 张辉；

【导师】 任兆玉；

【作者基本信息】 西北大学 ， 凝聚态物理， 2012， 硕士

【摘要】 Cs原子喷泉钟是目前复现“秒”定义时间频率基准装置,具有最高的准确度,作为基准钟标校其他原子钟,是一个国家时间频率系统的基础。Cs原子喷泉钟由光学系统,物理系统,电路系统与控制系统组成,以脉冲的方式工作。Cs原子喷泉钟光学系统提供铯原子操控与跃迁几率探测用的所有激光,是实现Cs冷原子样品,形成原子喷泉以及双能级探测的关键,其性能高低直接影响Cs原子喷泉钟整机运行及其性能指标,所以研制符合Cs原子喷泉钟整机运行要求的光学系统对于Cs原子喷泉钟而言是基础与关键。本文正是以NTSC-01型Cs原子喷泉钟光学系统研制为主要内容,其具体包括两个方面：1, NTSC-01喷泉钟光学系统的研制。NTSC-01喷泉钟光学系统提供Cs原子操控和跃迁几率探测用的所有激光。研制内容主要包括：(1)激光频率控制：包括激光光源频率稳定和AOM对光频率控制。采用饱和吸收光谱稳频,频率稳定度达到3×10-12/s。采用AOM对二维磁光阱预冷却光与三维磁光阱俘获光进行相应的频率失谐与快速移频,从而俘获与快速的操控原子按照控制系统时序进行上抛与探测。(2)激光功率放大与控制：包括冷却光与俘获光的放大和AOM对俘获光光功率的控制。采用注入行波放大器放大产生二维磁光阱的冷却光功率,注入锁定两台高功率从激光器产生三维磁光阱六束俘获光功率。AOM使六束俘获光功率在Cs原子上抛同时,在时序控制下按照指数规律衰减,使Cs原子按照偏振冷却机制进一步冷却。(3)激光传输：包括激光功率与偏振方向和保偏光纤的耦合。采用望远镜系统对功率进行耦合,通过消光比极值法与四分之一波片结合对激光偏振态与保偏光纤进行耦合。(4)激光束参量的调节。二维磁光阱冷却光与三维磁光阱俘获光通过一体化准直镜筒对其光斑质量特性进行调节,使其满足冷却与俘获Cs原子的光斑在准直性、方向性、功率、偏振态方面的要求。通过测量俘获Cs原子数目为2×109,并且Cs原子上抛81cm时下落信号的信噪比,符合NTSC-01喷泉钟后续实验的要求,说明光学系统满足了NTSC-01铯原子喷泉钟正常运行的要求。2,液晶频率调谐外腔半导体激光器的研究。基于液晶调谐电压低,回程误差小,无机械运动等特点,研制了一台基于LCVR频率调谐外腔半导体激光器。液晶电压改变1.6V,激光频率变化7GHz,覆盖了Cs原子D2线的全部饱和吸收谱线。采用“猫眼”式外腔结构使激光器具有一定的抗震性能,为替代传统冷却Cs原子激光光源提供了较好的选择。更多还原

【Abstract】 Cs atomic fountain clock is the reappearance of "seconds" definition of time and frequency standard device, has the highest accuracy, as a reference clock calibration with other atomic clock, is a time and frequency system based. Cs atomic fountain clock consists of the optical system, the physical system, circuit system and control system, in order to pulse mode.Cs atomic fountain clock optical system provides cesium atomic manipulation and transition probabilities for the detection of all laser, is the realization of Cs cold atomic samples, forming atomic fountain and two-level detection is the key, its performance directly affects Cs atomic fountain clock operation of the machine, the development of the Cs atomic fountain clock machine operation requirements the optical system for the Cs atomic fountain clock is the basis and key.The paper is based on the NTSC-01Cs fountain clock optical system as main content, which includes two aspects:1,NTSC-01fountain clock optical system. Optical system provide with Cs atom manipulation and transition probabilities for the detection of all laser. The research content mainly includes:(1),Laser frequency control:includes laser frequency stability and AOM on the optical frequency control. The saturated absorption frequency stabilization, frequency stability up to3X10-12/s Using AOM to two-dimensional magetic-optical trap pre-cooling laser and three-dimensional magneto-optical trap capture laser corresponding to the frequency detuning and fast frequency shift, so as to capture and rapid manipulation of atoms according to time series up and detection control system.(2),Laser power amplification and control:includes cooling and trapping laser amplification and AOM to capture laser power control. Laser power of Two-dimensional magneto-optical trap produce through injection into the traveling wave amplifier, and that of Three-dimensional magneto-optical trap generated by injected locking into two high power slave laser diode. Exponential decay of six capturing beam power makes atoms further cooling according to Sub-Doppler cooling mechanism when atom are launched under timing control. (3),Laser transmission:includes laser power and polarization and polarization maintaining fiber couping. Using telescope system for coupling power and quarter wave plate and extinction ratio measurement for coupling polarization between laser and polarization maintaining fiber.(4),Laser beam parameter optimization:it completed by adjusting laser expanded and collimation system, and make it meet cooling and capturing Cs atoms in laser collimation, direction, power, polarization state requirements.By measuring the capture atom number is2x10and intensity of time of flight at launching by81cm satisfy NTSC-01fountain clock follow-up requirements, It indicates that optical system can serve NTST-01successfully.2,Frequency tuning of external-cavity diode laser with liquid crystal. We report a frequency tunable external-cavity DFB laser using a liquid crystal variable retarder(LCVR) based on low tunable voltage and no hysterisis and mechanical moment. The laser frequency can span7GHz when bias voltage varies1.6V, covering all the saturated absorption spectroscopy of the Cs D2line. The external cavity of diode laser with a cat-eye reflector enhances stabitily of DFB laser. It is a better choice as an alternative to traditional cooling laser source.更多还原