Optical atomic magnetometry for ultra-low-field NMR detection

This chapter deals with detection of NMR signals in the ultra-low-field (ULF) regime, by means of optical atomic magnetometers. A general introduction is provided about specific NMR features occurring when nuclei precess in micro-Tesla fields, or weaker. The advantages of detecting the NMR signal by means of an optical atomic magnetometer are here preliminarly discussed. A further general introduction is provided about basic ideas and recent progresses in optical atomic magnetometry. A section is devoted to the detailed presentation of an example of dual-channel atomic magne- tometer which was used to detect the signal produced by protons of a remotely polarized water sample in an unshielded environment, taking advantage of its differential nature. Results reported in a wide set of similar experiments are then discussed in a general synthesis of the interdisciplinary activity performed on the main subject of this work. Emphasis is given to progresses in ULF imaging, in microfluidic, in setups designed for zero-field and near-zero-field NMR detection. The non-conventional NMR detection schemes discussed in this chapter are in some cases prof- itably coupled with non-conventional methods for sample polarization. Some experiments devoted to non-conventional preparation of the nuclear spin state are considered and briefly discussed, as well.