Automatic classification system of Raman spectra applied to pigments analysis

Raman spectroscopy is one of the few non-destructive techniques capable of identifying pigments in art works. Raman spectra contain powerful information that can be used to identify unknown compounds and their chemical structures. However, the analysis of spectral data comes with some difficulties, and therefore the spectral interpretation is not straightforward. Sometimes, there are very little differences in the spectral data concerning to specific identification objectives, for instance, in polymorphic discrimination or in the discrimination of natural and synthetic forms of certain pigments. Moreover, this discrimination is often performed manually so that the process can be repetitive, subjective and particularly time-consuming. The result is an increasing motivation to automate the identification process involved in the classification of pigments in paint. In this paper, we propose a system to automatically classify the spectral data into specific and well-known classes, i.e. reference classes. The proposal is based on a combination of chemometric techniques, which provides a powerful way to achieve spectral separability so that it is possible to discriminate between very similar spectra in an automatic way. In this regard, a decision-making algorithm was specifically developed to select the corresponding reference class with no user input, which was successfully validated using simulated spectra. The implemented methodology was used to classify Raman spectra of pigments commonly present in artist's paints in experimental cases, providing reliable and consistent results. Therefore, the presented system can play a good auxiliary role in the analysts' endpoint classification.Peer ReviewedPostprint (author's final draft

Automatic identification of artistic pigments by Raman spectroscopy using fuzzy logic and principal component analysis

This work offers an automatic identification system of Raman spectra of artistic pigments. The proposed methodology is based on a fuzzy logic system, and uses principal component analysis to reduce redundancies in data and the correlation operator as an index of similarity between two Raman spectra. Moreover, as sometimes pigments are used in mixtures by artist, the designed system is able to recognize binary mixtures of pigments on the basis of their Raman fingerprints.Peer ReviewedPostprint (published version

Morphology-based automated baseline removal for raman spectra of artistic pigments

The interpretation of a Raman spectrum is based on the identification of its characteristic molecular bands. However, the assignment of the vibrational modes is often compromised by the presence in the spectrum of an intense fluorescence background that covers the measured spectra. Several techniques have been employed to minimize the presence of this fluorescence in order to resolve and analyze Raman spectra. In this paper a new automated method for fluorescence subtraction is described, based on morphology operations. This method is compared with the most commonly used polynomial fitting methods. Results indicate that the proposed automated method is efficient in fluorescence subtraction and retains the line shapes and positions of the Raman bands in the spectra.Postprint (published version

Reduction of pulse distortion in travelling wave semiconductor optical amplifiers

The possibility of reducing the gain saturation during the pulse amplification process by means of the compensation of the carrier density variations is investigated. This should be useful in many optical systems and, especially, in high-speed communication systems.Peer ReviewedPostprint (published version

Técnicas de procesado de señal aplicadas al tratamiento de espectros Raman

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Influencia de los parámetros de un amplificador óptico en el valor óptimo del rendimiento cuántico del fotodetector en un enlace digital por fibra óptica

In this paper the performances introduced by a semiconductor optical amplifier in a fiber optical digital communication system are analyzed . The device is used as repeater as well as preamplifier at the photodetector input (PIN photodiode). It is shown that spontaneous emission and the number of repeaters give an upper limit for the quantum efficiency of the photodetector (which is a decisive parameter in the signal to noise ratio).Peer ReviewedPostprint (published version

Statistical analysis of nonlinear optical amplifier in high saturation

Peer ReviewedPostprint (published version

Amplificación de pulsos con amplificadores ópticos semiconductores

Peer ReviewedPostprint (published version

Microwave imaging with crossed linear arrays

The capabilities of a microwave imaging system working in air using two crossed linear arrays are described. The analytic expressions of the focusing procedures are derived, resolution and available volume of reconstruction are discussed. Finally, some experimental images corresponding to two dielectric objects are also shown.Peer ReviewedPostprint (published version

Aplicaciones del láser al análisis y tratamiento de obras de arte

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