激光雷达可以快速实现对大气风场的非侵入测量, 获得精确三维风矢量。为验证测风激光雷达观测湍流的可行性并获得湍流观测特征, 利用相干多普勒激光雷达在深圳杨梅坑进行湍流观测实验。依据 Reynolds 分解原理, 应用小波分解获取湍流脉动并分析大气的湍流运动特征。结果表明: 观测地日平均湍流强度呈现“单峰单谷”结构, 与实验期间气温的变化呈现较高相关性; 湍流动能引起垂直方向上的输送主要集中在日间 12:00 后, 与湍流耗散率的相关系数达 0.77; 湍流功率谱密度在惯性副区内基本符合 Kolmogorov“-5/3” 定律。研究结果验证了测风激光雷达可以较为精确地估算湍流参数。

相干多普勒激光雷达作为观测风场信息的有效探测工具,广泛应用于不同场景的风场以及大气观测。2019年8月,研究人员利用相干多普勒激光雷达在深圳市石岩综合气象观测基地连续开展了13 d的风廓线观测实验。分析了多普勒波束扫描模式下五波束法、三波束法和二波束法反演结果的异同及这些方法对测风精度和数据获取率的影响。数据比对结果表明,三波束法和二波束法的反演结果与五波束法所得结果有较好的一致性。针对激光雷达实际观测中系统或大气状态如云雾、降水等导致个别波束信噪比较低的问题,需灵活选取波束以反演风场、增加数据获取率,得到的探测高度平均提高量为100~400 m。

为了降低超稳光学腔的振动敏感度, 在综合考虑振动所导致的腔镜位移及转动后, 定义了一个新的表征腔体振动敏感度的参量。采用有限元数值分析方法, 用所定义的单一参量优化了一个典型的立式超稳光学腔。优化过程考虑了腔体端面直径、支撑孔位置和深度等关键几何参量。结果表明, 优化后的腔体结构和支撑方式可以明显降低超稳腔对振动的敏感度, 腔体稳定性比优化前提高1.5倍。该优化方法操作性强, 能够有效提升超稳腔仿真和设计的效率。

The laser cooling of ytterbium (Yb) atoms needs a 399-nm laser which operates on the strong 1S0 -1P1 transition and can be locked at the desired frequencies for different Yb isotopes. We demonstrate a frequency locking method using the fluorescence spectrum of an Yb atomic beam as a frequency reference. For unresolved fluorescence peaks, we make the spectrum of the even isotopes vanish by using the strong angular-dependence of the fluorescence radiations; the remained closely-spaced peaks are thus clearly resolved and able to serve as accurate frequency references. A computer-controlled servo system is used to lock the laser frequency to a single fluorescence peak of interest, and a frequency stability of 304 kHz is achieved. This frequency-locked laser enables us to realize stable blue magneto-optic-traps (MOT) for all abundant Yb isotopes.

A frequency-stabilized 556-nm laser is an essential tool for experimental studies associated with 1S0-3P1 intercombination transition of ytterbium (Yb) atoms. A 556-nm laser light using a single-pass second harmonic generation (SHG) is obtained in a periodically poled MgO:LiNbO3 (PPLN) crystal pumped by a fiber laser at 1111.6 nm. A robust frequency stabilization method which facilitates the control of laser frequency with an accuracy better than the natural linewidth (187 kHz) of the intercombination line is developed. The short-term frequency jitter is reduced to less than 100 kHz by locking the laser to a home-made reference cavity. A slow frequency drift is sensed by the 556-nm fluorescence signal of an Yb atomic beam excited by one probe beam and is reduced to less than 50-kHz by a computer-controlled servo system. The laser can be stably locked for more than 5 h. This frequency stabilization method can be extended to other alkaline-earth-like atoms with similar weak intercombination lines.

We build a Zeeman slower with consecutive coils and use it to load an Yb magneto-optical trap (MOTs). Cooling efficiency is measured by the fluorescence intensity of the atomic cloud trapped by the MOT. An optimized magnetic field profile can acquire the maximum cooling efficiency, corresponding to a good compromise between the smaller magnetic field mismatch and the high capture velocity. Our studies provide useful information on how the performance of the Zeeman slower can be improved.