The Research On Key Technologies Of Closed-Loop Spin-Exchange Relaxation-Free Atomic Magnetometer And Its Applications

The detection of ultra-weak magnetic field(～ft)was demonstrated to have potential applications in biomagnetism,such as magnetoencephalography(MEG)and magnetocardiography(MCG),geological exploration,fundamental physics research,ultra-low field magnetic resonance imaging(ULF MRI)and nuclear magnetic resonance(NMR).Spin-Exchange relaxation-free(SERF)atomic magnetometers are the new generation of extremely weak magnetic field sensors,which are based on the optical detection of the precession of electronic spins.Compared with the traditional detection instrument-superconducting quantum interference device(SQUID),the SERF magnetometers with intrinsic advantages of low-cost,non-cryogenic operation,miniaturization,and the closer detecting distance.This dissertation studies the topic of extremely weak magnetic field detection and its application.Based on the homebuilt dual-beam SERF atomic magnetometers experimental platform and the compact singlebeam atomic magnetometers,the high-resolution spectroscopy research and the MEG were carried out,and the measured results are as follows:(1)We developed a proportional-integral(PI)controller-based closed-loop SERF magnetometer with probe-pump-laser configuration.Specifically,the bandwidth of the SERF magnetometer was improved above 1.2 kHz while the sensitivity was maintained at 15 fT/Hz1/2 in a broader frequency range.A near 40-fold enhancement of the bandwidth was obtained in comparison with the open-loop system.Also,we demonstrated that the bandwidth of the proposed SERF magnetometer could be adaptively tuned to keep an optimal sensitivity in the needed frequency range for different applications.(2)On the basis of the researches above,we also designed and developed a fibercoupled atomic magnetometer with compact size(the outside dimension is only 15×22×30 mm3),high sensitivity and high bandwidth.Specifically,the bandwidth of the atomic magnetometer was extended to 675 Hz while the sensitivity was maintained at 22 fT/Hz1/2.A nearly 3-fold enhancement of the bandwidth was obtained in comparison with the open-loop control.The dynamic range has also been greatly improved and effectively reduces the requirement of the shielding environment.(3)A zero-to ultralow-field NMR was built based on the dual-beam SERF atomic magnetometers,which mainly consist of pre-polarization magnet,sample transporting device and the data acquisition device.The zero-field NMR spectra and the ultralowfield NMR spectra of 13CH3-COOH and 13CH3-OH were studied with the NMR spectrometer.The results depict that the zero-to ultralow-field NMR spectra exhibit a completely different characteristics with their high-field NMR spectroscopy,and provide the complementary information to high-field NMR.(4)The single channel MEG system was developed by using the homebuilt compact magnetometer,which mainly included magnetically shielded room,wearable helmet,control system,brain function stimulation device and data acquisition system.The single channel MEG system was successfully applied on measuring alpha rhythm and human auditory evoked fields(AEFs),which demonstrated a promising potential of such the homebuilt atomic magnetometer for future multi-channel MEG system.In summary,we developed a proportional-integral(PI)controller-based closedloop SERF magnetometer(dual-beam)and compact atomic magnetometers(singlebeam)with high bandwidth and high sensitivity.On the basis of the researches above,a zero-to ultralow-field NMR was built for the high-resolution spectra measurement.Moreover,we also designed and developed the single channel MEG system and successfully measured the human brain signal.This study provides the important support for promoting the deep innovation and development of related subjects.