Optical black hole lasers

Using numerical simulations we show how to realise an optical black hole laser, i.e. an amplifier formed by travelling refractive index perturbations arranged so as to trap light between a white and a black hole horizon. The simulations highlight the main features of these lasers: the growth inside the cavity of positive and negative frequency modes accompanied by a weaker emission of modes that occurs in periodic bursts corresponding to the cavity round trips of the trapped modes. We then highlight a new regime in which the trapped mode spectra broaden until the zero-frequency points on the dispersion curve are reached. Amplification at the horizon is highest for zero-frequencies, therefore leading to a strong modification of the structure of the trapped light. For sufficiently long propagation times, lasing ensues only at the zero-frequency modes.Comment: accepted for publication in Classical and Quantum Gravit

Collective dynamics of evanescently coupled excitable lasers with saturable absorber

We present a numerical study of the collective dynamics in a population of coupled excitable lasers with saturable absorber. At variance with previous studies where real-valued (lossy) coupling was considered, we focus here on the purely imaginary coupling (evanescent wave coupling). We show that evanescently coupled excitable lasers exhibit synchronization like the lossy coupled ones. Furthermore, we show that out-of-diagonal disorder-induced localization of excitability takes place for imaginary coupling too, but it can be frustrated by nonvanishing linewidth enhancement factor. Graphical abstract: [Figure not available: see fulltext.]

Array-enhanced synchronization and coherence resonance in coupled excitable semiconductor lasers

Summary form only given. We present a numerical study of the nonlinear dynamics of a population of coupled semiconductor lasers with saturable absorber operating in the excitable regime [1] and described by a set of coupled Yamada models [2]. In particular we have investigated the self-organized synchronization process taking place spontaneously among the lasers, showing significant correlations between the spike-like pulses emitted by different lasers. Our findings demonstrate that synchronization in time and also in intensity occurs in a large region of the parameter space and for different population sizes and furthermore it is robust with respect to random distribution of the lasers' pump parameter which is linked to the excitability threshol

Dynamic Behaviour of "Collapsible" Concrete

In this work a particular cement composite material for protection of structures and infrastructures against accidental actions, such as blast or impact, has been investigated. An experimental procedure has been developed in order to assess static and dynamic behaviour of energy absorbing cementitious composites. The granular cementitious composite has been studied focusing attention to compressive strength, high deformation and energy dissipation capacity which are important characteristics for an absorber material. An experimental characterization of the material behaviour under compressive static and dynamic loadings has been carried out. Different deformation velocities have been studied in order to define the material behaviour in a wide range of strain rates. The velocity range up to 0.1 m/s is investigated by means of a universal servo-hydraulic MTS 50 kN testing machine. Some preliminary results have been reported and discussed in the present work.JRC.G.4-European laboratory for structural assessmen

Spatial properties of twin-beam correlations at low- to high-intensity transition

It is shown that spatial correlation functions measured for correlated photon pairs at the single-photon level correspond to speckle patterns visible at high intensities. This correspondence is observed for the first time in one experimental setup by using different acquisition modes of an intensified CCD camera in low and high intensity regimes. The behavior of intensity auto- and cross-correlation functions in dependence on pump-beam parameters including power and transverse profile is investigated.Comment: 6 pages, 4 figures, accepted for publication in Optics Expres

Building Design for safety and sustainability

The issue of sustainability in the building industry is prominent, as this industry causes large impacts on the environment but also it contributes greatly in a socioeconomic perspective of growth. In line with sustainability the purpose of this report is twofold: to provide a comprehensive description of the current state-of-the-art building assessment methods and to contribute towards sustainability and building design optimisation through the introduction of a comprehensive design approach. In the first part of the report the role of the Environmental methods and Footprint schemes is examined, with a further analysis in the Footprint (PEF, OEF) methods introduced by the European Commission, in ascertaining building sustainability. Footprint schemes provide an environmental assessment on a product-level approach. However, a building is better described as a process rather than a product, while considering the interactions involved in the building life-cycle it seems inappropriate to consider building components in isolation. Current environmental assessment methods evaluate buildings over their life-cycle at a later design stage to provide an indication of their environmental performance. The sole aspect of environmental performance cannot provide comparable building solutions, while at this stage the information cannot effectively used in the general design process. A more effective way of achieving building sustainability is to consider and incorporate environmental issues in the early design stage, where the principles of durability, probabilistic reliability and safety of structures are involved. Since these parameters are part of the same whole they need to be designed together. To move towards sustainability, a new integrated-design approach is deemed essential that will allow building assessment in a multi-performance perspective. In the second part, the Sustainable Structural Design (SSD) methodology is presented built on environmental and structural performance parameters based on a life-cycle approach. Emphasis is put on integrating environmental results in the structural performance, which is treated in a probabilistic manner through the introduction of a simplified Performance-Based Assessment method. A global assessment parameter as the result of ecological costs and structural repair and downtime losses is obtained, which allows diverse stakeholder categories to make decisions in a multi-dimensional perspective. The final part of the report is devoted to further research insights. Both resource efficiency opportunities in the building sector and a respective Communication launched by the European Union in July 2014 are discussed.JRC.G.4-European laboratory for structural assessmen

COMB-REFERENCED COHERENT RAMAN SPECTROSCOPY ON PURE H2

\chem{H_2} is a benchmark system for testing quantum electrodynamics and physics beyond the standard model via highly accurate measurements of transition frequencies, which has been the subject of many works during the past decades\footnote{L. A. Rahn, R. L. Farrow, and G. J. Rosasco, Physical Review A, 43(11), 6075 (1991).}\footnote{G. D. Dickenson, M. L. Niu, et al., Physical review letters, 110(19), 193601 (2013).}\footnote{S. Kassi and A. Campargue, Journal of Molecular Spectroscopy, 300, 55-59 (2014).}. However, retrieving the unperturbed transition frequencies requires to measure spectra at very low pressure, where the low density combined with weak quadrupole transition moments makes it challenging to achieve high signal-to-noise ratios. An alternative approach is to model very precisely the transition profiles at higher pressure in order to correct for the strong Dicke narrowing and speed-dependent collisional effects which distort the absorption profiles. We present a new approach to measure \chem{H_2} transition frequencies in the fundamental rovibrational band with high accuracy and signal-to-noise ratio. The approach uses an optical frequency comb to calibrate the frequency spacing between a cw pump and a cw Stokes beams that interact with \chem{H_2} in a multipass cell by stimulated Raman scattering. Specifically, we focus on the Q(1) transition of the 1-0 band of pure \chem{H_2} at 4155.25\wn. The pump laser emits at 737.8 nm and is kept fixed while the Stokes laser is swept over 0.3\wn around 1064 nm. The wavelength of the Stokes laser is referenced to a local oscillator, which in turn is locked to an optical frequency comb along with the pump laser. The frequency comb is obtained using an Er:fiber amplified femtosecond laser with stabilized repetition rate and offset frequency to a reference Rb standard. The profiles measured at various pressures, spanning from 0.1 to 5 atm, are fitted using Hartmann-Tran profiles. The retrieved parameters are compared to $\it{ab}$-$\it{initio}$ values based on \chem{H_2}-\chem{H_2} quantum scattering calculations

Characterizing the non-classicality of mesoscopic optical twin-beam states

We present a robust tool to analyze nonclassical properties of multimode twin-beam states in the mesoscopic photon-number domain. The measurements are performed by direct detection. The analysis exploits three different non-classicality criteria for detected photons exhibiting complementary behavior in the explored intensity regime. Joint signal-idler photon-number distributions and quasi-distributions of integrated intensities are determined and compared with the corresponding distributions of detected photons. Experimental conditions optimal for nonclassical properties of twin-beam states are identified.Comment: 10 pages, 10 captioned figure

Applicability of the Sustainable Structural Design (SSD) method at urban/regional/national level

The alarming data on world climatic change, resources impoverishment and increasing human diseases caused by environmental pollution has encouraged the modern society to feel committed in reducing the environmental issues and to adopt a sustainable approach to every human activity. Sustainability is an ambitious challenge for Europe development and European policy is addressed in investing massive resources for achieving sustainable goals. Construction is one of the most impactful industrial sector because of the high consequences it generates on the society, the environment and the economy. Indeed, building constructions involve social aspects, as safety and comfort, economic aspects, as construction investments and maintenance, and environmental aspects, as energy consumption and emissions. The present study derives from the development of a building design method, called Sustainable Structural Design (SSD) Methodology. This methodology is based on a multi-performance and life cycle-oriented approach, which includes the environmental aspects, related to energy consumption and CO2 emissions, in structural design, performed with a simplified Performance Based Assessment (sPBA) methodology, in order to obtain a global assessment parameter in monetary terms. Moreover, the study derives from the awareness about the structural condition of the European building stock, which is old and, in some cases, far from the structural safety required by the European codes. Thus, a simply applicable methodology, allowing the identification of the territorial areas which need a more urgent intervention is necessary. The application of the SSD methodology at territorial level could allow the inclusion of the main aspects of sustainability, identifying the areas which an intervention could reduce the energy consumptions, the CO2 emissions and the structural losses of the included buildings. Thus, this report aims at studying the applicability of the SSD methodology at territorial level, considering three different area dimensions, as countries, regions and cities, and identifying the right approach for each of them. Consequently, an SSD methodology at territorial level is developed and illustrated.JRC.E.4-Safety and Security of Building

Absolute spectroscopy near 7.8 μm with a comb-locked extended-cavity quantum-cascade-laser

We report for the first time the frequency locking of an extended-cavity quantum-cascade-laser (EC-QCL) to a near-infrared frequency comb. The locked laser source is exploited to carry out molecular spectroscopy around 7.8 μm with a line-centre frequency combined uncertainty of ~63 kHz. The strength of the approach, in view of an accurate retrieval of line centre frequencies over a spectral range as large as 100 cm-1, is demonstrated on the P(40), P(18) and R(31) lines of the fundamental rovibrational band of N2O covering the centre and edges of the P and R branches. The spectrometer has the potential to be straightforwardly extended to other spectral ranges, till 12 μm, which is the current wavelength limit for commercial cw EC-QCLs