  Low thermal polarization of nuclear spins is a primary sensitivity limitation
for nuclear magnetic resonance. Here we demonstrate optically pumped
(microwave-free) nuclear spin polarization of $^{13}\mathrm{C}$ and
$^{15}\mathrm{N}$ in $^{15}\mathrm{N}$-doped diamond. $^{15}\mathrm{N}$
polarization enhancements up to $-2000$ above thermal equilibrium are observed
in the paramagnetic system $\mathrm{N_s}^{0}$. Nuclear spin polarization is
shown to diffuse to bulk $^{13}\mathrm{C}$ with NMR enhancements of $-200$ at
room temperature and $-500$ at $\mathrm{240~K}$, enabling a route to
microwave-free high-sensitivity NMR study of biological samples in ambient
conditions.
