Dipolar field effects in a solid-state NMR maser pumped by Dynamic Nuclear Polarization

We report the observation of pulsed solid state MASER from hyperpolarized proton spin system using Dynamic Nuclear Polarization (DNP) at cryogenic temperature. Induction decays exhibiting multiple asymmetric maser pulses and persistent for tens of second were observed in DNP experiments performed on negatively polarized water samples at cryogenic. These experiments a qualitatively reproduced by simulations of this non-linear spin dynamics by combining the Bloch-Maxwell equations for radiation damping that further incorporate dipolar interactions, on the one hand, and a simplified model of DNP, on the other hand.