Dipolar field effects in a solid-state NMR maser pumped by dynamic nuclear polarization.

We report the observations and the analysis of a pulsed solid state sustained maser generated by proton spins hyperpolarized by Dynamic Nuclear Polarization (DNP) at cryogenic temperatures. Similar unconventional behaviour was observed recently [Weber et al. , Phys. Chem. Chem. Phys. , 2019, 21 , 21278-21286], with induction decays exhibiting multiple asymmetric maser pulses for short time (100 ms) and persistent for tens of second, when the spins are polarized negatively. We present new evidence of such DNP NMR masers, and shed light on previously observed but unexplained features of these masers through simulations of the non-linear spin dynamics using the Bloch-Maxwell-Provotrov (BMP) equations for radiation damping and DNP, and taking into account the (distant) dipolar field.