  Chaotic oscillations of a linearly polarized single longitudinal-mode
thin-slice Nd:GdVO4 laser placed in a self-mixing laser Doppler velocity scheme
were dynamic characterized in terms the intensity probability distribution,
joint time-frequency analysis and short-term Fourier transformation of temporal
evolutions, and the degree of disorder in the amplitude and phase of the
long-term temporal evolutions. The transition from chaotic relaxation
oscillations (RO) to chaotic spiking oscillations (SO) was explored via the
chaotic itinerancy (CI) regime by increasing the feedback ratio toward the
laser from a rotating scattering object. The intensity probability distribution
was found to change from an exponential decay in the RO regime to an inverse
power law in the SO regime, which manifests itself in self-organized critical
behavior, while stochastic subharmonic frequency locking among the two
periodicities of RO and SO takes place in the CI regime featuring quantum-noise
(spontaneous emission)-induced order in the amplitude and phase of the spiking
oscillations. All of the experimental results were reproduced by numerical
simulations of a model equation of a single-mode self-mixing solid-state laser
subjected to Doppler-shifted optical feedback from a rotating scattering
object.
