Optically-pumped magnetometers (OPM) based on parametric resonance allow real-time tri-axial measurement of very small magnetic fields with a single optical access to the gas cell. Most of these magnetometers rely on circularly polarized pumping light. We focus here on the ones relying on linearly polarized light, yielding atomic alignment. For these magnetometers we investigate three second order effects which appear in the usual regimes of operation, so to clarify if they translate to metrological problems like systematic errors or increased noise. The first of these effects is the breakdown of the three-step approach when the optical beam has a large intensity. The second one is the breakdown of the rotating wave approximation when the frequencies of the RF fields are not much larger than the rates of other atomic processes. The third one is the tensor light-shift which appears when the light is slightly detuned from resonance. This work should help to clarify the accuracy reachable with OPM, which is an important question notably for medical imaging applications.

中文翻译：

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基于原子对准的参数共振磁力计的二阶效应

基于参量共振的光泵磁力计（OPM）可以通过单次访问气室的方式对很小的磁场进行实时三轴测量。这些磁力计大多数依赖于圆偏振泵浦光。在这里，我们将重点放在那些依赖于线性偏振光产生原子排列的光源上。对于这些磁力计，我们研究了在通常的运行方式中出现的三个二阶效应，以便弄清它们是否会转化为计量问题，例如系统误差或噪声增加。这些影响中的第一个是光束强度大时三步法的分解。第二个是当射频场的频率不大于其他原子过程的速率时旋转波近似的分解。第三个是张量光偏移，当光线从共振中稍微失谐时出现。这项工作应有助于阐明OPM可以达到的精度，这对于医学成像应用而言尤其重要。