  Polarizing nuclear spins is of fundamental importance in biology, chemistry
and physics. Methods for hyperpolarizing 13C nuclei from free electrons in
bulk, usually demand operation at cryogenic temperatures. Room-temperature
approaches targeting diamonds with nitrogen-vacancy (NV) centers could
alleviate this need, but hitherto proposed strategies lack generality as they
demand stringent conditions on the strength and/or alignment of the magnetic
field. We report here an approach for achieving efficient electron->13C spin
alignment transfers, compatible with a broad range of magnetic field strengths
and field orientations with respect to the diamond crystal. This versatility
results from combining coherent microwave- and incoherent laser-induced
transitions between selected energy states of the coupled electron-nuclear spin
manifold. 13C-detected Nuclear Magnetic Resonance (NMR) experiments demonstrate
that this hyperpolarization can be transferred via first-shell or via distant
13Cs, throughout the nuclear bulk ensemble. This method opens new perspectives
for applications of diamond NV centers in NMR, and in quantum information
processing.
