  Highly sensitive nuclear spin detection is crucial in many scientific areas
including nuclear magnetic resonance spectroscopy (NMR), imaging (MRI) and
quantum computing. The tiny thermal nuclear spin polarization represents a
major obstacle towards this goal which may be overcome by Dynamic Nuclear Spin
Polarization (DNP) methods. The latter often rely on the transfer of the
thermally polarized electron spins to nearby nuclear spins, which is limited by
the Boltzmann distribution of the former. Here we demonstrate the polarization
and read out of a nuclear spin bath consisting of $^{13}$C nuclear spins in
diamond by using a single nitrogen-vacancy (NV) center. Our method utilizes
microwave dressed states to transfer the NV's high ($>$~92~\%) non-equilibrium
electron spin polarization induced by short laser pulses to the surrounding
carbon nuclear spins, where the NV is repeatedly repolarized optically, thus
providing an effectively infinite polarization reservoir. A saturation of the
polarization in the nuclear "frozen core" is achieved, which is confirmed by
the decay of the polarization transfer signal and shows an excellent agreement
with theoretical simulations. Hereby we introduce the Polarization Read Out by
Polarization Inversion (PROPI) method as a quantitative magnetization measure
of the nuclear spin bath. Moreover, we show that using the integrated solid
effect both for single and double quantum transitions a nuclear spin
polarization can be achieved even when the static magnetic field is not aligned
along the NV's crystal axis. This opens a path for the application of our DNP
technique to spins in and outside of nanodiamonds, enabling their application
as MRI tracers.
