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Publicações

2022

Nematic Liquid Crystals as a Tabletop Platform for Studying Turbulence

Autores
Ferreira, TD; Silva, NA; Guerreiro, A;

Publicação
U.Porto Journal of Engineering

Abstract
Light propagating in nonlinear optical materials opens the possibility to emulate quantum fluids of light with accessible tabletop experiments by taking advantage of the hydrodynamical interpretation. In this context, various optical materials have been studied in recent years, with nematic liquid crystals appearing as one of the most promising ones due to their controllable properties. Indeed, the application of an external electric field can tune their nonlocal response, and this mechanism may be useful for producing fluids of light and developing optical analogues. In this work, we extend the applicability of nematic liquid crystal to support optical analogues and study the possibility of emulating turbulent phenomena by using two fluids of light. These fluids interact with each other through the nonlinearity of the medium and generate instabilities that will lead to turbulent regimes. We also explore the possibility of exciting turbulent regimes through the decay of dark soliton stripes. The preliminary results are presented.

2022

Effects of Pulse Duration in Laser-induced Breakdown Spectroscopy

Autores
Ferreira, MFS; Silva, NA; Guimarães, D; Martins, RC; Jorge, PAS;

Publicação
U.Porto Journal of Engineering

Abstract
Laser-induced breakdown spectroscopy (LIBS) is a technique that leverages atomic emission towards element identification and quantification. While the potential of the technology is vast, it still struggles with obstacles such as the variability of the technique. In recent years, several methods have exploited modifications to the standard implementation to work around this problem, mostly focused on the laser side to increase the signal-to-noise ratio of the emission. In this paper, we explore the effect of pulse duration on the detected signal intensity using a tunable LIBS system that consists of a versatile fiber laser, capable of emitting square-shaped pulses with a duration ranging from 10 to 100 ns. Our results show that, by tuning the duration of the pulse, it is possible to increase the signal-to-noise ratio of relevant elemental emission lines, an effect that we relate with the computed plasma temperature and associated density for the ion species. Despite the limitations of the work due to the low-resolution and small range of the spectrometer used, the preliminary results pave an interesting path towards the design of controllable LIBS systems that can be tailored to increase the signal-to-noise ratio and thus be useful for the deployment of more sensitive instruments both for qualitative and quantitative purposes.

2022

Towards robust calibration models for laser-induced breakdown spectroscopy using unsupervised clustered regression techniques

Autores
Silva N.A.; Capela D.; Ferreira M.; Gonçalves F.; Lima A.; Guimarães D.; Jorge P.A.S.;

Publicação
Results in Optics

Abstract

2022

Comprehensive comparison of linear and non-linear methodologies for lithium quantification in geological samples using LIBS

Autores
Ferreira, MFS; Capela, D; Silva, NA; Goncalves, F; Lima, A; Guimaraes, D; Jorge, PAS;

Publicação
SPECTROCHIMICA ACTA PART B-ATOMIC SPECTROSCOPY

Abstract
Laser-induced breakdown spectroscopy allows fast chemical analysis of light elements without significant sample preparation, turning it into a promising technique for on-site mining operations. Still, the performance for quantification purposes remains its major caveat, obstructing a broader application of the technique. In this work, we present an extensive comparison of the performances of distinct algorithms for quantification of Lithium in a mining prospection stage, using spectra acquired with both a commercial handheld device and a laboratory prototype. Covering both linear and non-linear methodologies, the results show that, when covering a wide range of concentrations typical on a mining operation, non-linear methodologies manage to achieve errors compatible with a semi-quantitative performance, offering performances better than those obtained with linear methods, which are more affected by saturation and matrix effects. The findings enclosed offer support for future applications in the field and may possibly be generalized for other elements of interest in similar mining environments.

2022

Towards robust calibration models for laser-induced breakdown spectroscopy using unsupervised clustered regression techniques

Autores
Silva, NA; Capela, D; Ferreira, M; Gonçalves, F; Lima, A; Guimarães, D; Jorge, PA;

Publicação
Results in Optics

Abstract