基于电子顺磁共振谱的残磁测量应用及进展

Electron paramagnetic resonance, which is similar to nuclear magnetic resonance, is a method based on the paramagnetism and Zeeman splitting of electron magnetic moments in an external magnetic field. It is associated with unpaired electrons inside matter and external magnetic fields. Extremely weak magnetic fields are generally defined as those on the order of nT or less. Currently, scientific research is often conducted in extremely weak magnetic environments, such as basic physics research, biomagnetism of the heart and brain, etc. Therefore, stable and reliable magnetic shielding is often used to create the required environment. Magnetic shielding includes passive magnetic shielding and active magnetic compensation. Passive magnetic shielding refers to using a magnetic shielding chamber to shield the external magnetic field, which often has a certain amount of residual magnetic field inside. To facilitate further active magnetic compensation, it is necessary to detect the residual magnetic field inside shielding. At present, the means of measuring the residual magnetic field in the shielding room are mainly divided into commercial magnetometer measurement and in-situ measurement. The commercial magnetometer measurement method is simple, with low accuracy and high noise, and it is not conducive to miniaturization. With low noise, in-situ measurements are the main method of study now. Since the outermost layer of the alkali metal atom contains an unpaired electron, it becomes an ideal sample for electron paramagnetic resonance experiments. With the development of laser and optical pumping, it has been realized to probe the electron paramagnetic resonance spectrum of alkali metal atoms by Faraday rotation. The in-situ measurement of residual magnetic fields by related electron paramagnetic resonance spectrum of alkali metal vapor is profitable and precise and has great promise for application. Usually, the electron paramagnetic resonance-based residual magnetometry system includes the residual magnetic environment and sample module, the optical probe module, the signal modulation module, the environmental monitoring module, and the data acquisition and procession module, with the core being the optical probe module, which determines the sensitivity of the magnetic field measurement. This paper briefly describes the principle of the electron paramagnetic resonance technique, introduces typical magnetometers based on this technique and current developments with a focus on optically-pumped magnetometers, and outlines the residual magnetometry system based on electron paramagnetic resonance spectroscopy, each component module and the current development of related technologies in recent years.