Transient Bimodality Research Articles

Critical slowing-down phenomena in an InSb optically bistable étalon

We report the first known direct observation of the critical slowing-down effect and transient bimodality in an intrinsic semiconductor all-optically bistable device with a cw CO laser holding beam and a PbSSe diode laser switching beam. The measurements of critical slow-down effects show good agreement with the numerical model using a modified Debye dynamic equation. The switching profile has been shown to depend on both the size of the hysteresis loop and the diode pulse parameter. A scaling law for the delay time of the switching when external parameter P changes close to the critical value Pc has been indicated to fit (P − Pc)−1/2.

Transient bimodality in optically bistable systems.

We analyze the main features of transient bimodality in optically bistable systems. This phenomenon is proved to exhibit a nonmonotonic behavior in its dependence on the noise level, because a decrease of noise first enhances and subsequently damps the transient bimodality. Hence we identify a range of noise levels which characterizes the phenomenon. In this range the most probable switching time exhibits a remarkably linear dependence on the logarithm of the noise parameter. We discuss the dependence of the phenomenon on the distance from the critical point, especially in connection with the experiments on critical slowing down. Our results show a very satisfactory qualitative agreement with the recent experiments on transient bimodality performed by Lange and collaborators. We argue that our picture holds in general for a large class of systems which exhibit the phenomenon of transient bimodality.

Transients in optical bistability: Experiments with external noise

The influence of noise on an optical bistable system in the vicinity of one of the bifurcation points is investigated by studying the transient response to a step input of light. The experiment is performed under absorptive conditions in a sodium-filled nonlinear Fabry-Perot in the bad cavity limit. Alternatively, a bistable electronic circuit (Schmitt trigger) is shown to exhibit the same type of behavior while admitting more detailed studies. On the monostable side of the bifurcation point, we observe a transient bimodality as well as a shift of the average switching delay to shorter times with increasing noise. Both results are in accord with a recent prediction by Broggi and Lugiato. We also present indications that the average switching time is smoothly connected with the lifetime of the metastable state on the bistable side of the bifurcation point.

Study of fluctuations in transient optical bistability.

The effect of external noise on the dynamic behavior of an intrinsic optical-bistable system is studied experimentally. Under conditions of critical slowing down we observe a transient bimodality in the intensity distribution as well as a reduction of the switching delay due to fluctuations. Our experimental results are in good qualitative agreement with theoretical predictions.

Stochastic analysis of explosive behaviour: A qualitative approach

In many instances, the evolution of physico-chemical systems involves a long slow induction period followed by an abrupt switching to a final stable attractor. In the present paper the properties of fluctuations during this explosive stage of evolution are analyzed. Qualitative arguments, confirmed by an exactly soluble model, establish that this regime is characterized by the development of long tails and multiple humps in the probability distribution. The implications of this phenomenon of transient bimodality are discussed.

Brain stem auditory evoked response development in the kitten

The development of brain stem auditory evoked responses (BAERs), recorded from a surface electrode as short-latency, volume-conducted potentials, was studied in a series of kittens over a postnatal period ranging from birth to 60 days. Repeated, longitudinal observations on particular kittens were supplemented with observations on additional kittens during the first and second postnatal week to determine age of onset of the BAERs. The position of the animal and sound source within the recording chamber were held constant across recording sessions, as was click intensity except during recordings in which intensity effects were specifically studied. Click rates of 1, 10, 50 and 100/sec were routinely presented. Reference electrodes at the tongue, pinna and neck showed volume-conducted responses to the click stimuli and resulted in considerable distortion of the activity recorded by the vertex electrod; the forepaw, in contrast, showed no activity and a vertex-forepaw electrode configuration provided good resolution of the BAERs across development. A number of new observations were made. BAERs were first observed at 4 days of age, approximately the same age at which depth evoked potentials are first recorded in brain stem auditory nuclei. Initially the BAERs were diffuse, high threshold and fatigued rapidly, characteristics shared with depth evoked potentials in the early postnatal period. Over the first two weeks, the potentials showed marked decrease in threshold, increased resistance to fast click rates, and better definition of wave forms. All BAER components showed exponential decreases in latency. Because all of the brain stem evoked potentials could be recorded concurrently and longitudinally in the same subject a number of developmental comparisons were possible among the BAER components. Wave 1, related to the acoustic nerve in the adult cat, showed a developmental time course and adult latency similar to that reported for N 1. Wave 2, related to the cochlear nucleus in the adult, showed a marked bimodality over the first month; wave 2a was a large amplitude clearly separated wave which gradually fused as an inconspicuous conspicuous leading shoulder on wave 2b. Wave 2b developed with a time course and adult latency similar to that reported for the ventral cochlear nucleus. Wave 3, related to the region of the superior olivary complex in the adult, showed a clear but transient bimodality during the third week of development. Wave 5, related to the inferior colliculus in the adult, appeared later than waves 1–4 and showed a significantly slower rate of development than waves 1–4. These data indicate that differential developmental changes occur within the brain stem auditory pathway and that the BAERs provide a dynamic probe of concurrent maturational interactions.