A cosmological concordance model with dynamical vacuum term

We demonstrate that creation of dark-matter particles at a constant rate implies the existence of a cosmological term that decays linearly with the Hubble rate. We discuss the cosmological model that arises in this context and test it against observations of the first acoustic peak in the cosmic microwave background (CMB) anisotropy spectrum, the Hubble diagram for supernovas of type Ia (SNIa), the distance scale of baryonic acoustic oscillations (BAO) and the distribution of large scale structures (LSS). We show that a good concordance is obtained, albeit with a higher value of the present matter abundance than in the ΛCDM model. We also comment on general features of the CMB anisotropy spectrum and on the cosmic coincidence problem.     

Second harmonic generation by modal phase matching involving optical and plasmonic modes

The feasibility of a modal phase matching scheme between optical modes and surface plasmonic modes is demonstrated: in fact, the high effective index of a plasmonic mode allows us to obtain phase matching even in semiconductors showing a large dispersion between fundamental and second harmonic wavelengths. We design a realistic device to obtain Type-II second harmonic generation in AlGaAs-based waveguides; whereas one of the two pumps is carried by a plasmonic mode, the generated second harmonic signal is guided inside the AlGaAs multilayer, and hence it is not hampered by high propagation losses.     

Time domain bidirectional beam propagation method for second harmonic generation in multilayers

We propose a time domain bidirectional beam propagation method based on scattering operators for wide band pulse propagation in nonlinear multilayers. The reported numerical examples demonstrate the applicability of the algorithm for the analysis of temporal effects related to the process of second harmonic generation.     

Phase-matched SHG in periodically poled LiNbO3 waveguides: A novel configuration

We present a feasiblity study of a new method for enhancing the continuously phase matched second harmonic generation in 2D PPLN optical waveguides fabricated using the off-center Czochralski technique and proton-exchange. We show that a periodic variation of the nonlinear coefficient along the transverse coordinate permits for efficient energetic exchanges.     

Periodically poled lithium niobate structures grown by the off-center Czochralski technique for backward and forward second harmonic generation

We report on the characterization of periodically poled lithium niobate structures grown by the off-center Czochralski technique with periods ranging between 2 and . The domains distribution along the crystal was inspected by a profilometer scan after etching the structures and carrying a suitable data processing. The second harmonic generation efficiency was predicted by numerically integrating the governing equations through to a recently proposed nonlinear bidirectional beam propagation method. The numerical analysis pointed out the feasibility of the backward second harmonic generation in the sample with the shortest domain period. The predicted second harmonic generation efficiency was finally corrected considering the phase shifts induced in the second harmonic wave by the presence of different sized domains.     

Bidirectional beam propagation method for second-harmonic generation in engineered multilayered waveguides

By employing an iterative procedure based on a bidirectional beam propagation method with perfectly matched layers, we develop a numerical algorithm to model light propagation in engineered multilayered nonlinear waveguides. Examples are given for multilayered structures and segmented waveguides designed for second-harmonic generation.     

Modeling and Characterization of Border Domain Effects in Periodically Poled Lithium Niobate Crystals Grown by the Off-center Czochralski Technique

We report on the optical characterization of periodically poled lithium niobate crystals grown through the Czochralski off-center technique. The optical diffraction technique pointed out that refractive index changes occur at the border domain. Their effect on the second harmonic generation is therefore investigated by numerical analysis in order to predict the conversion efficiency of the grown crystals.