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.Comment: 5 page

Multiple choice homework as a cost-effective and efficient tool for student self-training

A self-training scheme geared at inducing students to improve their skills through independent homework is presented. The motivation is to identify an inexpensive, yet effective tool for raising the competence level of students in the Fundamental Sciences (in particular Physics). Since globally existing financial restrictions do not allow for extensive supervised work, a scheme is devised where the additional personal training is rewarded through bonuses in the grade, while safeguarding against the danger of cheating. Overburdening the instructors is avoided through the use of computer-based grading of homework, while a carefully chosen bonus plan, weighted by the grades obtained in supervised tests, counters the effects of potential cheating.Comment: 9 pages with 3 figure

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.Comment: 14 pages, 14 figures in colo

Stochastic Simulator for modeling the transition to lasing

A Stochastic Simulator (SS) is proposed, based on a semiclassical description of the radiation-matter interaction, to obtain an efficient description of the lasing transition for devices ranging from the nanolaser to the traditional "macroscopic" laser. Steady-state predictions obtained with the SS agree both with more traditional laser modeling and with the description of phase transitions in small-sized systems, and provide additional information on fluctuations. Dynamical information can easily be obtained, with good computing time efficiency, which convincingly highlights the role of fluctuations at threshold.Comment: 5 pages, 3 figures, 1 tabl

Comment on "Qualitative Measurement of Rubidium Isotope Ratio Using Forward Degenerate Four-Wave-Mixing", Spectrochimica Acta B 70, 39 (2012)

No abstract available, since this is a Comment on a published article (cf. title)Comment: This paper is withdrawn, since the Editor suggested that a new version be resubmitted as a Letter. The new version is entitled: Letter to the Editor of Spectrochimica Acta B: External versus self-induced ac Stark shif

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

High-resolution birefringence cartography of a vertical cavity semiconductor laser

We couple a double-channel imaging technique, allowing for the simultaneous acquisition of high-quality and high-resolution intensity and peak emission wavelength profiles [T. Wang and G.L. Lippi, Rev. Sci. Instr. 86, 063111 (2015)], to the polarization-resolved analysis of the optical emission of a multimode VCSEL. Detailed information on the local wavelength shifts between the two polarized components and on the wavelength gradients can be easily gathered. A polarization- and position-resolved energy balance can be constructed for each wavelength component, allowing in a simple way for a direct analysis of the collected light. Applications to samples, other than VCSELs, are suggested

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.Comment: 11 pages. Submitted for the Conference Proceedings of Photonics Europe 2014 -- paper # 9134-3

Analytical vs. Numerical Langevin Description of Noise in Small Lasers

We compare the analytical and numerical predictions of noise in nano- and microcavity lasers obtained from a rate equation model with stochastic Langevin noise. Strong discrepancies are found between the two approaches and these are critically analyzed and explained on the basis of general considerations and through the comparison to the numerical predictions of a Stochastic Laser Simulator. While the analytical calculations give reliable redictions, the numerical results are entirely incorrect thus unsuitable for predicting the dynamics and statistical properties of small lasers.Comment: 5 pages, 4 figure

Dynamics at Threshold in Mesoscale Class-B Lasers

The threshold properties of very small lasers (down to the nanoscale) are a topic of active research in light of continuous progress in nanofabrication. With the help of a simple rate equation model we analyze the intrinsic, macroscopic dynamics of threshold crossing for Class B lasers. We use the deterministic aspects of the basic rate equations to extract some fundamental time constants from an approximate analysis of laser dynamics in the threshold region. Approximate solutions for the population inversion and for the field intensity, up to the point where the latter reaches macroscopic levels, are found and discussed. The resulting timescales characterize the laser's ability to respond to perturbations (external modulation or intrinsic fluctuations in the lasing transition region). Numerical verifications test the accuracy of these solutions and confirm their validity. The predictions are used to interpret experimental results obtained in mesoscale lasers and to speculated about their extension to nanolasers.Comment: 12 pages, 8 figures. Part of this manuscript was submitted as arXiv:1601.01872. We have added an experimental section and rewritten parts of the text for a different audienc