基于电子顺磁共振谱的残磁测量应用及进展

Application and Progress of Residual Magnetometry Based on Electron Paramagnetic Resonance Spectroscopy

电子顺磁共振类似于核磁共振,是一种基于电子磁矩在外磁场中的顺磁性及塞曼分裂的方法,该方法与物质中未成对电子和外磁场相联系,通过获取和分析物质的电子顺磁共振谱,能够得到物质的结构信息或环境的磁场信息,因此其常被用来分析物质结构、探测磁场等。极弱磁场通常指nT或以下量级的磁场,目前一些科学研究的进行常常要求在极弱磁环境下进行,例如基础物理研究、心脑磁探测等,因此稳定可靠的磁屏蔽常被用来创建所需的极弱磁环境。磁屏蔽包括被动磁屏蔽和主动磁补偿,被动磁屏蔽指利用磁屏蔽室屏蔽外界磁场,其内部往往有一定量的残余磁场,因此为方便进一步主动磁补偿,探测屏蔽后的残余磁场是有必要的。目前屏蔽室内残余磁场的测量手段主要分为商用化磁强计测量和装置原位测量,商用化磁强计测量方法简单,但精度低、噪声大,且不利于小型化,利用装置原位测量能够减少噪声,是目前主要的研究方法。由于碱金属原子最外层含有一个未成对电子,其成为电子顺磁共振实验的理想样品。而随着激光和光泵技术的发展,利用法拉第旋光效应作为光学手段探测气体原子的电子顺磁共振谱已经成为了可能。通过测量碱金属原子气体的电子顺磁共振谱进行残余磁场的原位测量效果好、精度高,具有极大的应用前景。通常基于电子顺磁共振的残磁测量系统包括残磁环境和样品模块、光学探头模块、信号调制模块、环境监测模块以及信号收集与处理模块,核心是光学探头模块,决定了磁场测量的灵敏度。简要描述了电子顺磁共振技术的原理,以光泵磁力计为主介绍了基于该技术的典型磁力计和目前的发展,重点概述了基于电子顺磁共振谱的残磁测量系统、各个组成模块以及相关技术近年来的发展现状。

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.