Coherent multi-mode dynamics in a Quantum Cascade Laser: Amplitude and Frequency-modulated Optical Frequency Combs

We cast a theoretical model based on Effective Semiconductor Maxwell-Bloch Equations and study the dynamics of a multi-mode mid-Infrared Quantum Cascade Laser in Fabry Perot with the aim to investigate the spontaneous generation of optical frequency combs. This model encompasses the key features of a semiconductor active medium such as asymmetric,frequency-dependent gain and refractive index as well as the phase-amplitude coupling of the field dynamics provided by the linewidth enhancement factor. Our numerical simulations are in excellent agreement with recent experimental results, showing broad ranges of comb formationin locked regimes, separated by chaotic dynamics when the field modes unlock. In the former case, we identify self-confined structures travelling along the cavity, while the instantaneous frequency is characterized by a linear chirp behaviour. In such regimes we show that OFC are characterized by concomitant and relevant amplitude and frequency modulation

Municipal Solid Waste, Market Competition and the EU Policy

Two of the main pillars of the EU solid waste policy are the Proximity Principle and the Self-Sufficiency Principle. According to those, waste should be disposed as close as possible to where it has been produced. A likely effect of such provision is to prevent competition from neighbouring areas and increase the market power of local disposers, with possible undesirable consequences for other firms in the vertical chain. We show through a simple spatial model that one additional effect of the Proximity Principle and of the Self-Sufficiency Principle is to provide an incentive to collectors and waste producers to increase the amount of separated waste

First record of Panulirus regius (Decapoda: Palinuridae) in the Italian seas, with remarks on the earlier Mediterranean records

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Retrieval of the Dielectric Properties of a Resonant Material in the Terahertz Region via Self-Detection Near Field Optical Microscopy

We present a numerical and analytical study of the self-detection scattering type near field optical microscopy (SD s-SNOM), a recently demonstrated technique based on a combination of self-mixing interferometry and scattering near-field microscopy. This scheme, which exploits a terahertz (THz) quantum cascade laser as both a laser source and detector, allows to investigate the optical properties of resonant materials in the THz range with resolution far beyond the diffraction limit. Our study, developed by using a modified version of the Lang-Kobayashi model, is focused on the weak feedback regime (Acket parameter C approximate to 10(-1)), where we derive an approximated method for the retrieval of the scattering coefficient of the SD s-SNOM configuration applied to a sample of Cesium Bromide (CsBr). These results were used in turn to derive the dielectric permittivity of the sample, reporting a good accuracy in the estimation of its phonon resonances

Frequency combs and optical feedback in Quantum Cascade Lasers: a unifying theoretical framework

We propose a unified theoretical framework for the frequency comb formation and optical feedback effects in semiconductor lasers. We use the quantum cascade laser as a suitable device to develop the framework unifying these two research areas, so far treated distinctly. We generate a novel feedback regime diagram and we provide a proof of principle that feedback can be used to induce and manipulate frequency combs, selecting their harmonic order. These results open a pathway towards new methodologies for hyperspectral imaging, multimode coherent sensing, and multi-channel communication

Dynamics of Optical Frequency Combs in Ring and Fabry-Perot Quantum Cascade Lasers

Since the demonstration that multimode Quantum Cascade Lasers (QCLs) can operate as sources of Optical Frequency Combs (OFC) [1] , an extended class of theoretical models, based on standard two or three level Maxwell-Bloch equations, has been proposed to interpret such phenomenology

SATELLITE AND IN SITU GROUND TEMPERATURE

Ground thermal anomalies in volcanic-hydrothermal systems, where the outflow of hot fluids gives rise to fumarolic fields, soil degassing, and hot soils, have, up to now, rarely been investigated by using satellite. Here we report a comparison between surface temperature derived by satellite data and a large data set of measured soil temperatures and CO2 fluxes for a volcanic-hydrothermal system, the Solfatara of Pozzuoli (Campi Flegrei, Italy). Surface temperatures derived from ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) data are compared with soil temperatures and CO2 fluxes from four surveys performed in 2003, 2010, and in 2014. The good match between the spatial distributions of computed and measured temperatures suggests the adequacy of satellite data to describe the Solfatara thermal anomaly, while the correspondence between temperatures and CO2 fluxes, evidences the link between degassing and heating processes. The ASTER derived surface temperatures (14–37°C) are coherent with those measured in the soil (10–97°C at 10 cm depth), considering the effect of the thermal gradients which characterize the degassing area of Solfatara. This study shows that satellite data can be a very powerful tool with which to study surface thermal anomalies, and can provide a supplementary tool to monitor thermal evolution of restless volcanoes

Unified theory for frequency combs in ring and Fabry-Perot quantum cascade lasers: an order-parameter equation approach

We present a unified model to describe the dynamics of optical frequency combs (OFCs) in quantum cascade lasers (QCLs), incorporating both ring and Fabry-P\'erot (FP) cavity configurations. The model derives a modified complex Ginzburg-Landau equation (CGLE), leveraging an order parameter approach and is capable of capturing the dynamics of both configurations, thus enabling a comparative analysis. In the modified CGLE, a nonlinear integral term appears which is associated with the coupling between counterpropagating fields in the FP cavity and whose suppression yields the ring model, which is known to be properly described by a conventional CGLE. We show that this crucial term holds a key role in inhibiting the formation of harmonic frequency combs (HFCs), associated to multi-peaked localized structures, due to its anti-patterning effect. We provide in support a comprehensive campaign of numerical simulations, in which we observe a higher occurrence of HFCs in the ring configuration compared to the FP case. Furthermore, the simulations demonstrate the model's capability to reproduce experimental observations, including the coexistence of amplitude and frequency modulation, linear chirp, and typical dynamic scenarios observed in QCLs. Finally, we perform a linear stability analysis of the single-mode solution for the ring case, confirming its consistency with numerical simulations and highlighting its predictive power regarding the formation of harmonic combs

Investment Sharing in Broadband Networks

This paper presents a model of competition between an incumbent firm and an Other Licensed Operator (OLO) in the broadband market, where the incumbent has an investment option to build a Next Generation network (NGN) and it can do so by making an investment sharing agreement with the OLO, or alone. Two different kinds of investment sharing contractual forms are analysed, a basic investment sharing, where no side-payment is given for the use of the NGN between co-investors, and joint-venture, where a side-payment is set by the co-investing firms. Results show that investment sharing can potentially be beneficial in terms of competition and investments, but the number of firms involved matters and so does the choice of the NGN access price, for insiders and outsiders of the agreement. Even when the presence of firms outside of the agreement force insiders to compete more fiercely, there might be a concern with the potential exclusion of the outsiders from the NGN