arXiv subjects

G. L. Lippi

Publications and source records attributed to G. L. Lippi.

23 records · Page 2Linked to original sources

arXiv2014

Beyond the standard approximations: an analysis leading to a correct description of phase instabilities in semiconductor lasers

Following an overview of modeling of (longitudinal) multimode semiconductor laser dynamics, we analyze in detail a model proposed in 2006 to explain deterministic, phase-locked modal alternation, experimentally observed a decade ago. Through a stability analysis, we prove that the numerically obtained electromagnetic field evolution, interpreted as an explanation of the experiments, is nothing more than an extremely long transient, so long as to be hardly identifiable in an entirely numerical approach. Comparison with a model we have recently derived, which predicts a phase instability (Benjamin-Feir-like) compatible with the experimental observations, highlights the crucial ingredient for the dynamics. The wide spectrum of unstable eigenvalues accompanying the phase instability plays the role of an equivalent noise in a fully deterministic description, thus reconciling the heuristic models which could qualitatively reproduce the experimental observation either with deterministic equations in the presence of mode-coupling, or through stochastically driven modal decompositions.

physics.optics↗

arXiv2014

A priori analysis: an application to the estimate of the uncertainty in course grades

The a priori analysis (APA) is discussed as a tool to assess the reliability of grades in standard curricular courses. This unusual, but striking application is presented when teaching the section on data treatment of a Laboratory Course to illustrate the characteristics of the APA and its potential for widespread use, beyond the traditional Physics Curriculum. The conditions necessary for this kind of analysis are discussed, the general framework is set out and a specific example is given to illustrate its various aspects. Students are often struck by this unusual application and are more apt to remember the APA. Instructors may also benefit from some of the gathered information, as discussed in the paper.

physics.ed-ph↗

arXiv2014

Phase Instability as a Source of Modal Dynamics in Semiconductor Lasers

Thanks to a new derivation of the fundamental equations governing multimode dynamics for a semiconductor laser near its threshold, we identify regimes of existence of a pure phase instability (and of a mixed phase-amplitude turbulence regime) which give an alternative satisfactory interpre- tation of the deterministic multimode dynamics observed in some devices. The existence of intrinsic noise generated by the phase instability reconciles in the same description the deterministic and random features of the semiconductor dynamics.

physics.optics↗

arXiv2014

Fast dynamics and spectral properties of a multilongitudinal-mode semiconductor laser: evolution of an ensemble of driven, globally coupled nonlinear modes

We analyze the fast transient dynamics of a multi-longitudinal mode semiconductor laser on the basis of a model with intensity coupling. The dynamics, coupled to the constraints of the system and the below-threshold initial conditions, imposes a faster growth of the side modes in the initial stages of the transient, thereby leading the laser through a sequence of states where the modal intensity distribution dramatically differs from the asymptotic one. A detailed analysis of the below-threshold, deterministic dynamical evolution allows us to explain the modal dynamics in the strongly coupled regime where the total intensity peak and relaxation oscillations take place, thus providing an explanation for the modal dynamics observed in the slow, hidden evolution towards the asymptotic state (cf. Phys. Rev. A 85, 043823 (2012)). The dynamics of this system can be interpreted as the transient response of a driven, globally coupled ensemble of nonlinear modes evolving towards an equilibrium state. Since the qualitative dynamics do not depend on the details of the interaction but only on the structure of the coupling, our results hold for a whole class of globally, bilinearly coupled oscillators.

physics.optics↗

arXiv2003

Recoil-induced lasing

The interaction of an atomic gas confined inside a cavity with a strong electromagnetic field is numerically and theoretically investigated in a regime where recoil effects are not negligible. The spontaneous appearance of a density grating (atomic bunching) accompanied by the onset of coherent backpropagation is found to be ruled by a continuous phase-transition. Numerical tests allow us to convincingly prove that the transition is steered by the appearence of a periodic atomic density modulation. Consideration of different experimental relaxation mechanisms induces us to analyze the problem in nearly analytic form, in the large detuning limit, using both a Vlasov approach and a Fokker-Planck description. The application of our predictions to recent experimental findings, reported in [Phys. Rev. Lett. {\bf 91}, 183601 (2003)], yields a semi-quantitative agreement with the observations.

physics.optics↗