  We propose a highly efficient dynamic nuclear polarization technique that is
robust against field in-homogeneity. This technique is designed to enhance the
detection sensitivity in nano-MRI, where large Rabi field gradients are
required. The proposed technique consists of an adiabatic half passage pulse
followed by an adiabatic linear sweep of the electron Rabi frequency and can be
considered as an adiabatic version of nuclear orientation via electron spin
locking (adiabatic-NOVEL). We analyze the spin dynamics of an electron-nuclear
system that is under microwave irradiation at high static magnetic field and at
cryogenic temperature. The result shows that an amplitude modulation of the
microwave field makes adiabatic-NOVEL highly efficient and robust against both
the static and microwave field in-homogeneity.
