Figure 3

Efficient DNP using NVs of random axis orientation. (a) The parallel dynamical nuclear polarization dynamics with microwave driving fields of multiple time-dependent frequencies. The microwave wire is assumed to be perpendicular to the direction of the magnetic field. (b) The polarization dynamics of a ¹³C at a distance of 1.5 nm using single NV center with different symmetry axis (NV axis) orientation. \(P_{\downarrow}\) is the nuclear spin down state population, and the central frequency of microwave field \(\omega_{0}(t)\) changes at the speed of \({\nu=1\mbox{ MHz}\cdot\mbox{ms}^{-1}}\). (c) The average nuclear spin down state population \(\bar {P}_{\downarrow}\) as a function of the total polarization time t for the frequency changing speed \(\nu=0.75\mbox{ MHz}\cdot\mbox{ms}^{-1}\) and \(\nu=0.5\mbox{ MHz}\cdot\mbox{ms}^{-1}\), using an ensemble of NV centers with random NV axis orientations. In both (a) and (b), the magnetic field is \(B=250\mbox{ G}\), the amplitude of microwave field is \({\Omega=\gamma_{C} B}\), where \(\gamma_{C}\) is the gyromagnetic ratio of ¹³C, and the NV center is re-polarized every 100 μs.