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Publications

Publications by CAP

2020

Inscription of surface waveguides in glass by femtosecond laser writing for enhanced evanescent wave overlap

Authors
Amorim, VA; Maia, JM; Viveiros, D; Marques, PVS;

Publication
JOURNAL OF OPTICS

Abstract
Near-surface optical waveguides were fabricated in alkaline earth boro-aluminosilicate glass (Eagle2000), by femtosecond laser direct writing, using two distinct approaches. First, the capability of directly inscribing optical waveguides close to the surface was tested, and then, compared to the adoption of post writing wet etching to bring to the surface waveguides inscribed at greater depths. Laser ablation was found to limit the minimum surface to core center distance to 6.5 mu m in the first method, with anisotropic wet etching limiting the latter to 3 mu m without any surface deformation; smaller separations can be achieved at the cost of the planar surface topography. Furthermore, the waveguide's cross-section was seen to vary for laser inscription nearing the surface, observations that were also corroborated by its distinct guiding characteristics when compared to the adoption of post writing wet etching. The spectral analysis (in the 500-1700 nm range) also evidenced an increase in insertion loss for longer wavelengths and smaller surface to core center separations, caused, most likely, by coupling loss due to the interaction between the propagating mode and the surface. Different lengths of waveguide exposed to the surface were also tested, revealing that scattering loss due to surface roughness is not an issue at the centimeter scale.

2020

Dissipative solitons in an atomic medium assisted by an incoherent pumping field

Authors
Silva, NA; Almeida, AL; Ferreira, TD; Guerreiro, A;

Publication
JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS

Abstract
This work models the propagation of an optical pulse in a four-level atomic system in the electromagnetically induced transparency regime. By demonstrating that linear and nonlinear optical properties can be externally controlled and tailored by a continuous-wave control laser beam and an assisting incoherent pump field, it is shown how these media can provide an excellent framework to experimentally explore pulse dynamics in the presence of non-conservative terms, either gain or loss. Furthermore, we explore the existence of stable dissipative soliton solutions, testing the analytical results with computational simulations of both the effective (1+1)-dimensional model and the full Maxwell-Bloch system of equations.

2020

Using numerical methods from nonlocal optics to simulate the dynamics of N-body systems in alternative theories of gravity

Authors
Ferreira, TD; Silva, NA; Bertolami, O; Gomes, C; Guerreiro, A;

Publication
PHYSICAL REVIEW E

Abstract
The generalized Schrodinger-Newton system of equations with both local and nonlocal nonlinearities is widely used to describe light propagating in nonlinear media under the paraxial approximation. However, its use is not limited to optical systems and can be found to describe a plethora of different physical phenomena, for example, dark matter or alternative theories for gravity. Thus, the numerical solvers developed for studying light propagating under this model can be adapted to address these other phenomena. Indeed, in this work we report the development of a solver for the HiLight simulations platform based on GPGPU supercomputing and the required adaptations for this solver to be used to test the impact of new extensions of the Theory of General Relativity in the dynamics of the systems. In this work we shall analyze theories with nonminimal coupling between curvature and matter. This approach in the study of these new models offers a quick way to validate them since their analytical analysis is difficult. The simulation module, its performance, and some preliminary tests are presented in this paper.

2020

Bridging the hydrodynamic Drude model and local transformation optics theory

Authors
Alves, RA; Guerreiro, A; Navarro Cia, M;

Publication
PHYSICAL REVIEW B

Abstract
The recent ability of plasmonic nanostructures to probe subnanometer and even atomic scales demands theories that can account for the nonlocal dynamics of the electron gas. The hydrodynamic Drude model (HDM) captures much of the microscopic dynamics of the quantum mechanical effects when additional boundary conditions are considered. Here, we revisit the HDM under the Madelung formalism to reexpress its coupled system of equations as a single nonlinear Schrodinger equation in order to have a natural quantum mechanical description of plasmonics. Specifically, we study the response of two overlapping nanowires with this formalism. We ensure that an proposed frame concurs with classical electrodynamics when the local response approximation holds in the plasmonic system by finding the correction needed.

2020

Surface Plasmon Resonance sensor based on a D-shaped photonic crystal fiber with a bimetallic layer

Authors
Cardoso, MP; Silva, AO; Romeiro, AF; Giraldi, MTR; Costa, JC; Santos, JL; Baptista, JM; Guerreiro, A;

Publication
EPJ Web of Conferences

Abstract
The investigation of a D-shaped photonic crystal fiber sensor with a bimetallic layer for operation at the visible and infrared spectra is presented. The bimetallic layer is composed by silver and gold slabs deposited adjacently on the flat face of the fiber. It is shown that this architecture allows the excitation of two sharply distinguished plasmon resonance, which suggest potential applications for multiparameter sensing.

2020

Behavior of Listeria monocytogenes in beef Sous vide cooking with Salvia officinalis L. essential oil, during storage at different temperatures

Authors
Moura Alves, M; Gouveia, AR; de Almeida, JMMM; Monteiro Silva, F; Silva, JA; Saraiva, C;

Publication
LWT-FOOD SCIENCE AND TECHNOLOGY

Abstract
This study aims to evaluate the effect of Salvia officinalis L. (sage) essential oil (EO) on behavior of L. monocytogenes ATCC679 inoculated in beef processed by Sous-vide cook-chill (SVCC) and stored at 2 or 8 degrees C during 28 days. Minimum inhibitory concentration (MIC) of L. monocytogenes was obtained with 31.3 mu L/mL of EO. D values were determined for samples with EO (21'39 '') and without EO (21'17 ''). Beef samples were inoculated with L. monocytogenes at a concentration of 1 x 108 CFU/mL and vacuum-packed after EO addition at MIC value. Three heat treatments (F) were applied to reduce 1-log10 (F1), 2-log10 (F2) and 3-log10 (F3). EO composition was identified by gas-chromatography mass-spectrometry analysis. The main compounds identified were beta-pinene (11.70%), camphor (8.21%), beta-thujene (7.82%), 1.8-cineole (5.19%), alpha-humulene (6.07%) and endoborneol (4.87%).A reduction of approximately 1 log (CFU/g) of L. monocytogenes was observed in EO samples, compared to control samples at 2 degrees C. At 8 degrees C, despite exponential development from day 14, lower L. monocytogenes counts were observed in EO samples. Data showed that sage EO can help to control L. monocytogenes growth. However a possibility of using sage as a natural preservative, must be combined with other agents to control microbial growth more effectively.

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