Abstract
Cavity optomechanical magnetic field sensors, constructed by coupling a magnetostrictive material to a micro-toroidal optical cavity, act as ultra-sensitive room temperature magnetometers with tens of micrometre size and broad bandwidth, combined with a simple operating scheme. Here, we develop a general recipe for predicting the field sensitivity of these devices. Several geometries are analysed, with a highest predicted sensitivity of 180 p at 28 m resolution limited by thermal noise in good agreement with previous experimental observations. Furthermore, by adjusting the composition of the magnetostrictive material and its annealing process, a sensitivity as good as 20 p may be possible at the same resolution. This method paves a way for future design of magnetostrictive material based optomechanical magnetometers, possibly allowing both scalar and vectorial magnetometers.
Highlights
Magnetometers with high spatial resolution are required for many applications such as magnetoencephalography [1], measurements of topological spin configurations [2] and nuclear magnetic resonance spectroscopy to identify chemical composition, molecular structure and dynamics [3]
We present a model of magnetostrictive magnetometers that accounts for arbitrary mechanical mode shape and device geometry
We have developed a new versatile approach to model the sensitivity of optomechanical magnetometers, introducing magnetostriction into the elastic wave equation used to solve for mechanical eigenmodes
Summary
Magnetometers with high spatial resolution are required for many applications such as magnetoencephalography [1], measurements of topological spin configurations [2] and nuclear magnetic resonance spectroscopy to identify chemical composition, molecular structure and dynamics [3]. Optical readout of magnetometers can offer high sensitivity for a given resolution, while being well decoupled from the magnetic signal. An ensemble of nitrogen-vacancy (NV) centres with a volume size of 8.5×105 μm pushes the sensitivity down to 1 pT/ Hz [4]. [4]), as well as complicated microwave decoupling sequences in NMR spectroscopy, and is limited by the sample fabrication reproducibility [5]. It is crucial yet challenging to reduce the size of magnetometers while maintaining competitive sensitivities
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