Developments Of Atomic Magnetometer And Applications In Magnetic Resonance Imaging

We report the design and optimization of atomic magnetometer with a sensitivity of 80 fT/(Hz)1/2 for dc magnetic fields. Quantitative measurements using optically detected magnetic resonance imaging (MRI) for flow inside porous metals will be demonstrated. Flow profiles and images were obtained for a series of porous metals with different average pore sizes. The signal amplitudes and spatial distributions were compared. A clogged region in one of the samples was revealed using optically detected MRI but not optical imaging or scanning electron microscopy. These applications will significantly broaden the impact of optically detected MRI in chemical imaging and materials research. However, MRI in an ultralow magnetic field usually has poor spatial resolution compared to its high-field counterpart. The concomitant field effect and low signal level are among the major causes that limit the spatial resolution. A novel imaging method, a zoom-in scheme, will be demonstrated to achieve a reasonably high spatial resolution of 0.6 mm × 0.6 mm without suffering the concomitant field effect. This method involves multiple steps of spatial encoding with gradually increased spatial resolution but reduced field-of-view. This method takes advantage of the mobility of ultralow-field MRI and the large physical size of the ambient magnetic field. We also demonstrate the use of a unique gradient solenoid to improve the efficiency of optical detection with an atomic magnetometer. The enhanced filling factor improved the signal level and consequently facilitated an improved spatial resolution.