SERF (Spin-exchange relaxation free) atomic magnetometers have been demonstrated as the ultra-high sensitive, noncryogenic sensor. Single-beam configured sensors often choose VCSEL (Vertical-Cavity Surface-Emitting Laser) as the optical source. The existing commercial VCSELs are often with magnetic package and heater, which will affect the sensitivity of atomic magnetometers. In our work, we presented a novel nonmagnetic VCSEL package and its driver circuit. VCSEL chip, heater, and PT1000 are assembled on FPC (Flexible Printed Circuit), and its driver are optimized in terms of low noise, safe protection and AC temperature control. The result showed that the magnetic field generated by heating current can be ignored based on proposed layout method, and the RMS noise of current and temperature are lower than 0.1 µA and 20 mK, respectively. Our proposed method will expand the possibility for commercialization process of miniature SERF atomic magnetometers.
The whispering gallery mode ( WGM ) microcavity is a widely used microresonator. With its ultra-high quality factor Q ( above 109 ) and small mode volume ( µm3 ) , it can amplify the interaction between substances. The giant magnetostrictive material Terfenol-D is a rare earth material that can respond to changes in the magnetic field. With its ultra-high magnetostrictive coefficient ( 1500∼2000 ppm ), ultra-fast response speed( less than 1 µs ), and efficient energy conversion efficiency ( about 50% ), it is widely used in magnetic field sensors. Therefore, a high-sensitivity cavity optomechanical magnetometer can be designed and manufactured by combining the WGM and Terfenol-D. By analyzing the inherent characteristic frequency and magnetostrictive material characteristics of the cavity optomechanical magnetometer, the sensitivity of the magnetometer in magnetic field detection is greatly improved by mixing the bias magnetic field with the excitation magnetic field. In our simulation, compared with the environment without bias magnetic field, the deformation of the cavity optomechanical magnetometer is about 106 times higher of the original after adding the bias magnetic field, which will greatly enhance the detection sensitivity of the excitation magnetic field and provide an effective method for detecting biomagnetic signals.
Organisms have extremely low-frequency(below hundreds of Hz) weak magnetic field strength signals, such as the human heart, brain and other magnetic field signals, which are often even smaller at the pT level. It is of great significance to detect and locate diseases such as myocardial infarction and coronary heart disease in the human body by detecting magnetic field signals. Because the whispering gallery mode(WGM) microcavity has a high quality factor and a small mode volume, it can effectively amplify the interaction between substances, so it is an excellent platform for realizing ultra-high magnetic sensing sensitivity. By combining whispering gallery mode microcavities with magnetostrictive materials, highly sensitive magnetic sensors can be designed and fabricated. However, at present, the main application of microcavity magnetic sensor is in high frequency, and the detection of low frequency magnetic field is still difficult. We optimized the structural parameters of the sensor including the device radius, device thickness, base radius, magnetostrictive material type, microcavity structure and other parameters, significantly reducing the eigenfrequency of the sensor. The eigenfrequency of the sensor can reach 67 Hz, when the cavity with 1.5 mm radius size. The sensor eigenfrequency can be reduced to hundreds of Hz, in radius sizes of hundreds of micrometers. It will pave the way for the applications in low-frequency magnetic field detection.
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