磁场精密测量一直与人们的生产、生活息息相关，在导航定位、地质勘探、空间磁场、生物医疗、基础物理等多个领域均有广泛应用。原子磁力仪利用原子的相干内态提取磁场信息，往往表现出高灵敏度和高精度的优越测磁性能，成为了磁场测量实验研究阶段和商用产品转化的重点发展对象。论文以提高磁力仪的灵敏度为根本目的，相继研究了两种磁场精密测量新方法——基于原子的拉曼激射主动型测磁方法和自旋自持再生测磁方法。拉曼激射主动型磁场测量方法通过碱金属原子基态的塞曼能级发生双光子跃迁，产生拉曼散射光作为种子光在原子介质中不断放大，并在光学谐振腔反复振荡，最终形成激射光出射。这是一种主动型测量方式，整个过程不再受限于系统的闭环反馈延迟，而是对原子自发产生并在谐振腔重新建立的稳定振荡信号直接测量。当外磁场发生变化时，系统能快速响应，实时跟踪待测物理量的变化。通过拉曼激射光和泵浦光的拍频信号中心频率反映待测磁场强度。单次测量的信号信噪比可达50 dB，线宽为330 Hz，对应的测磁灵敏度为0.47 fT/√Hz@1 Hz。因此，利用这种测磁方法有望实现超高灵敏度主动型原子磁力仪。自旋自持再生方法通过原子态相干制备和无损探测方式，使系统输出的原子自旋进动信号持续稳定振荡。由于信号每个周期的相位初始时刻参考了前次周期的相位演化，信号相位相干时间突破原子弛豫寿命一个量级以上，使得系统的测量噪声在Allan 标准差分析中呈现快速1/τ下降。与一般原子磁力仪的1/√τ性质相比，这种1/τ测量表明系统的累积误差随测量时间增长而不再增加，为一常数，并且系统的噪声不确定度能快速接近量子噪声极限，在相同测量时间尺度上可获得更优越的灵敏度性能。论文首先介绍了自旋自持再生磁场测量系统的具体实现方案，接着在该系统下分别做了磁场梯度、矢量磁场和大磁场测量(地磁场量级)三类实验。两套相同的自旋自持再生原子磁力仪信号通过混频、滤波技术获得差分信号反映磁场梯度大小。系统对磁场梯度测量的灵敏度为186 fT/√Hz @ 0.1-2Hz，接近系统量子噪声极限(~100 fT/√Hz)，对环境共模噪声的抑制程度达90%。系统对矢量磁场的测量灵敏度为642 fT/√Hz @ 1 Hz，对磁场方位角的测量不确定为3.5*10^6 rad/s。在大磁场测量中，系统的启动时间小于20 ms，然而受磁场梯度噪声影响，测磁灵敏度为55 pT/√Hz @ 1 Hz @ 20000 nT。
The precision measurements of magnetic field have always been related to our life,being widely applied in many fields such as navigation and positioning, geological exploration, space physics, biomedical, basic physics and so on. The atomic magnetometers use the coherent internal state of the atom to extract the magnetic field information. Due to their superior performances with high sensitivity and high precision, they become key development objects for experimental researches and transformations of commercial products on the magnetic measurement. In order to further improve the sensitivity of themagnetometer, the paper has studied two new methods of magnetic field measurements - the active Raman lasing and the spin self-sustaining methods.The method of active Raman lasing causes a two-photon transition through the Zeeman level on the ground state of an alkali metal atom. The Raman scattered light, as a seed light, is continuously amplified in an atomic medium and oscillated in an optical resonant cavity, finally forming the lasing light. It is an active measurement method. The entire process measures the oscillation signal generated by the atoms directly without limitation by the closed-loop feedback delay of the system. When the external magnetic field changes, the system can respond quickly, and track the changes in real time. Theintensity of the magnetic field can be measured by the center frequency of the beat signal of the Raman laser light and the pump light. In a single measurement, the signal to noise ratio of the measured signal can reach 50 dB, the full width at half maximum (FWHM) is 330 Hz, and the corresponding magnetic sensitivity is 0.47 fT√Hz @ 1 Hz. Therefore, it is expected to achieve active atomic magnetometer with ultra-high sensitivity by themethod of Raman lasing. The spin self-sustaining method keeps coherent oscillations of the atomic spin precession signals through coherent preparation of atomic states and non-destructive detection. Since each period’s initial phase of the signal refers to the previous phase evolution, the phase coherence time of the signal exceeds the atomic relaxation lifetime by more than one order of magnitude, making the measurement noise of the system present a rapid 1/τ decline in the Allan deviation analysis. Compared with the 1/√τ property, the 1/τ measurement indicates that the cumulative error of the system is a constant with the increase of the measurement time. Besides, the noise uncertainty of the system can quickly close to the quantum-noise limit, showing a better sensitivity of magnetic field measurement on the same measurement time scale. Firstly, the paper introduces the scheme of the spin self-sustaining method for magnetic field measurement system. Then, three kinds of experiments are done under the system, including magnetic field gradient measurement, vector magnetic field measurement and magnetic field measurement under geomagnetic field magnitude. Through mixing and filtering, the differential signal by two sets of spin self-sustaining atomic magnetometer is applied to measure the magnitude of magnetic field gradient. The sensitivity of the magnetic field gradient measurement is 186 fT/√Hz@ 0.1-2 Hz, being close to the quantum-noise limit of the system(~100 fT/√Hz). The magnetic gradiometer can suppress the common noise of the environment up to 90%. The sensitivity of the vector magnetic field measurement is 642 fT/√Hz @ 1 Hz with 3.5*10^6 rad/s of the magnetic field azimuth angle’s uncertainty. In the magnetic fieldmeasurement under geomagnetic field magnitude, the startup of the system is less than 20 ms, and the sensitivity turns to 55 pT/√Hz@1 Hz@20000 nT as a result of the increase of magnetic field gradient noise.
