Developed An Ultra-high Sensitivity Atomic Magnetometer For Detecting Brain Magnetic

In recent years,the rapid scientific advances,both theoretical and experimental,lead to development and improvement of high-sensitivity atomic magnetometers(AMs).Able to operate in the spin-exchange relaxation free(SERF)regime,they now achieve some of the highest sensitivities in weak magnetic field measurements.These new sensors do not require cryogenic cooling and can thus be miniaturized to achieve sensor array sizes noticeably smaller than Superconducting QUantum Interference Devices(SQUIDs),which constitutes a considerable advantage.The detection of weak magnetic fields is widely used in geological exploration,military submarine detection and biomedicine.Especially in the field of magnetoencephalography(MEG),the optically-pumped atomic magnetometers have been highly anticipated,and are expected to become the magnetic sensors of the next generation in MEG equipment,replacing the SQUIDs.In this thesis,the experimental scheme consists of an atomic magnetometer with a single laser beam,equipped with field modulation coils and operating in the SERF regime.Our miniature single-sensor,quad-channel magnetometer for MEG was fabricated using 3D printing technology and self-developed instruments.The atomic magnetometer is based on the alkali metal potassium,with a vapor cell size of 8 mm × 8 mm ×8 mm.The magnetic gradient sensitivity was measured to be less than 6 f T /?Hz,and the external sensor dimensions are 20 mm × 40 mm × 190 mm.We used the sensor as a magnetometer for detection of neuromagnetic fields,using the steady-state visually evoked potential(SSVEP)paradigm.The brain signal induced by the steady-state visual stimulus corresponds in frequency to the visual stimulus,with the brain generating signals of the same frequency and its harmonics.Using a measurement time of 30 s,the magnetic signal of the brain was obtained for all four channels of the single sensor.The signal intensity range was 150-300 f T and the signal to noise ratio(SNR)was 3.5 ? 5.5.This signal strength was higher than in comparable measurements using SQUID sensors because the atomic magnetometer can be placed closer to the head.Compared with the electroencephalography(EEG)equipment,the SNR of the atomic magnetometer was slightly lower,but this metric did not suffer much from fluctuations.With the expected upgrades and optimization,the AMs could achieve better SNR than the EEG equipment.Another advantage over EEG is that the measurements do not require liquid gel,improving comfort of the subjects,shortening preparation time and allowing for longer acquisitions.The research work in this thesis lays the foundation for subsequent application of atomic magnetometers in MEG,specifically in the diagnosis of brain diseases,in cognitive research and in brain-computer interfacing(BCI).