Description DNP performed at liquid helium temperature (4.2 K) is used to drive the nuclear spins out of equilibrium up to a ≈ 80 − 90% hyperpolarized state by transferring the high polarization of unpaired electron spins through hyperfine or super-hyperfine interactions. The obtained hyperpolarized compounds can then be transferred to a solution state NMR spectrometer in dissolution-DNP (D-DNP) experiments that yield signal enhancements up to 4 orders of magnitude. The large magnetization in the NMR sample induces a significant feedback field from the detecting circuit - the improperly called “radiation damping”- and leads to nonlinear phenomena, such as sustained masers that prolong the signal coherence to tens of seconds or even hours. Alternatively, we have also generated stable and sustained masers in solution, by electronically controlling the radiation feedback phenomenon, and observed multimode NMR masers.