77,052 research outputs found
Frequency versus relaxation oscillations in a semiconductor laser with coherent filtered optical feedback
We investigate the dynamics of a semiconductor laser subject to coherent delayed filtered optical feedback. A systematic bifurcation analysis reveals that this system supports two fundamentally different types of oscillations, namely relaxation oscillations and external roundtrip oscillations. Both occur stably in large domains under variation of the feedback conditions, where the feedback phase is identified as a key quantity for controlling this dynamical complexity. We identify two separate parameter regions of stable roundtrip oscillations, which occur throughout in the form of pure frequency oscillations
Dynamic relaxation oscillations in a nonlinearly driven quartz crystal
We demonstrate thermo-mechanical relaxation oscillations in a strongly driven
quartz crystal. Dynamic bifurcation leads to two stable oscillation states with
a distinct electrical impedance. Slow Joule-heating, which shifts the
susceptibility of the crystal, provides a feedback that leads to
thermally-induced oscillations, in which the amplitude of the crystal is
modulated by a relaxation cycle. The frequency of the relaxation cycle is
roughly a million times lower than the resonance frequency of the crystal, and
it can be adjusted by the detuning from the critical point for dynamic
bifurcation. The experimental observations are reproduced by a simple model
that takes into account the slow dynamics of the system.Comment: Main text: 8 pages, 4 figures. Supplementary information: 4 pages, 3
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Spatiotemporal Oscillation Patterns in the Collective Relaxation Dynamics of Interacting Particles in Periodic Potentials
We demonstrate the emergence of self-organized structures in the course of
the relaxation of an initially excited, dissipative and finite chain of
interacting particles in a periodic potential towards its many particle
equilibrium configuration. Specifically we observe a transition from an in
phase correlated motion via phase randomized oscillations towards oscillations
with a phase difference between adjacent particles thereby yielding the
growth of long time transient spatiotemporal oscillation patterns. Parameter
modifications allow for designing these patterns, including steady states and
even states that combine in phase and correlated out of phase oscillations
along the chain. The complex relaxation dynamics is based on finite size
effects together with an evolution running from the nonlinear to the linear
regime thereby providing a highly unbalanced population of the center of mass
and relative motion
Birefringence controlled room-temperature picosecond spin dynamics close to the threshold of vertical-cavity surface-emitting laser devices
We analyze the spin-induced circular polarization dynamics at the threshold of vertical-cavity surface-emitting lasers at room-temperature using a hybrid excitation combining electrically pumping without spin preference and spin-polarized optical injection. After a short pulse of spin-polarized excitation, fast oscillations of the circular polarization degree (CPD) are observed within the relaxation oscillations. A theoretical investigation of this behavior on the basis of a rate equation model shows that these fast oscillations of CPD could be suppressed by means of a reduction of the birefringence of the laser cavity
Long-time discrete particle effects versus kinetic theory in the self-consistent single-wave model
The influence of the finite number N of particles coupled to a monochromatic
wave in a collisionless plasma is investigated. For growth as well as damping
of the wave, discrete particle numerical simulations show an N-dependent long
time behavior resulting from the dynamics of individual particles. This
behavior differs from the one due to the numerical errors incurred by Vlasov
approaches. Trapping oscillations are crucial to long time dynamics, as the
wave oscillations are controlled by the particle distribution inhomogeneities
and the pulsating separatrix crossings drive the relaxation towards thermal
equilibrium.Comment: 11 pages incl. 13 figs. Phys. Rev. E, in pres
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