Nonlinear effects from dipolar interactions in hyperpolarized liquid 129Xe.

We investigate nonlinear effects of long-range dipolar interactions in a spherical sample of hyperpolarized liquid 129Xe. Using two high-T(c) SQUID detectors we directly measure the evolution of the magnetization gradients. For small initial rf tip angles we observe an increase in the transverse relaxation time T2* by a factor of 5 and coherent oscillations of magnetization gradients. For large tip angles we observe an exponential growth of the magnetization gradients and demonstrate a gain in sensitivity to magnetic field gradients by a factor of 10. Our results are in quantitative agreement with simple analytical predictions. We discuss applications of these nonlinear effects for precision measurements.