In-situ Overhauser-enhanced nuclear magnetic resonance at less than 1 μT using an atomic magnetometer.

The development of atomic magnetometers has led to nuclear magnetic resonance (NMR) in zero and ultralow magnetic fields without using cryogenic sensors. However, in-situ detection, meaning that a sample locates in the detection space beside a vapor cell, has been conducted only with parahydrogen-induced polarization. Other hyperpolarization techniques remain unexplored yet. In this work, we demonstrate that Overhauser dynamic nuclear polarization allows in-situ NMR detection with an atomic magnetometer at less than 1 μT. The H NMR signal of a nitroxide radical solution was observed at 13.83 Hz, which corresponds to 325 nT. Signal-to-noise ratio was 32 after sixteen averages. On the Larmor precession of H spins, a decaying oscillation was superimposed. We attribute it to a transient Rb spin precession in response to a non-adiabatic field variation. This work shows a new capability of zero- and ultralow-field NMR.