Low-field microwave-mediated optical hyperpolarization in optically pumped diamond.

The emergence of a new class of optically polarizable electronic spins in diamond, nitrogen vacancy (NV) defect centers, has opened interesting new avenues for dynamic nuclear polarization. Here we review methods for the room-temperature hyperpolarization of lattice C nuclei using optically pumped NV centers, focusing particular attention to a polarization transfer via rotating-frame level anti-crossings. We describe special features of this optical DNP mechanism at low-field, in particular, its deployability to randomly oriented diamond nanoparticles. In addition, we detail methods for indirectly obtaining high-resolution NV ESR spectra via hyperpolarization readout. These mechanistic features provide perspectives for interesting new applications exploiting the optically generated C hyperpolarization.