Andrews, N. L. P., J. Z. Fan, R. L. Forward, M. C. Chen, and H.-P. Loock. “Determination of the Thermal, Oxidative and Photochemical Degradation Rates of Scintillator Liquid by Fluorescence EEM Spectroscopy.” Physical Chemistry Chemical Physics 19, no. 1 (2017): 73–81.
We present observations of an NMR maser (microwave ampliﬁcation by stimulated emission of radiation) of hyperpolarized 1H nuclei by dynamic nuclear polarization (DNP) at 1.2 K and in a magnetic ﬁeld of 6.7 T. The sustained maser pulses originate from the interplay between radiation damping (RD) due to the large 1H magnetization, and the remagnetization to a negative value by the DNP process. NMR signals lasting for several tens of seconds are thus observed on an ensemble of dipolar-coupled nuclear spins. Magnetization dynamics are analyzed in terms of the combined Bloch-Maxwell and Provotorov (BMP) equations for RD and DNP. Insight into the long time evolution of the magnetization is provided by a theoretical analysis of this nonlinear dynamical system, and by ﬁtting the NMR signal to a simpliﬁed version of the BMP equations.