Observation of noise-triggered chaotic emissions in an NMR-maser.

We report a new phenomenon observed when the magnetization of dissolved hyperpolarized (129)Xe is intense and opposite to the Boltzmann magnetization. Without radio-frequency (rf) excitation, the system spontaneously emits a series of rf bursts characterized by very narrow bandwidths (0.03 Hz at 138 MHz). This chaotic NMR-maser illustrates the increase in the complexity of spin dynamics at high magnetization levels by unveiling an inhomogeneous spatial organization of the xenon magnetization and an apparent dependence of the xenon transverse relaxation time on its polarization and/or on time.