As shown in Figures , these signals exhibit long series of maser bursts of approximately constant intensities and regularly spaced, except for the very first one. This first maser burst immediately follows the trigger rf pulse, its peak intensity is roughly ∼ 10 times larger and its duration accordingly shorter, than those of the next maser pulses. This feature is reproducible in all the experiments giving rise to sustained masers. Besides, and although such sustained maser pulses were easily reproduced, their duration and the delay between them could vary between different experiments in an uncontrolled way. A striking feature of the observed sustained masers is the absence of decay of the maser pulse intensities with time (except for the initial one), suggesting that the magnetization reaches a pseudo-periodic asymptotic dynamics kind of regime. However, some irregularities appeared in these experiments, with the appearance of maser pulses of various widths and at random delays between them.2c However, in all our experiments, these were transient behavours that never led to a chaotic dynamics.