Experimental characterization of Shil'nikov chaos by return times

We report experimental evidence of a new type of chaos characterized by pulses equal in shape, but irregularly separated in time. The times of return to a Poincaré section are statistically spread, however their iteration map is one-dimensional and in close agreement with that arising from Shil'nikov theory. Thus, the iteration map of the time intervals becomes the most appropriate indicator of this chaos. The residual width of the experimentally measured maps is due to a transient fluctuation enhancement peculiar to macroscopic systems, which is absent in low-dimensional chaotic dynamics.