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International audience; The etching of semiconductors and metals by a photonic jet (PJ) generated with a shaped optical ber tip is studied. Etched marks with a diameter of 1 micron have been realized on silicon, stainless steel and titanium with a 35 kHz pulsed laser, emitting 100 ns pulses at 1064 nm. The selection criteria of the ber and its tip are discussed. We show that a 100/140 silica ber is a good compromise which takes into account the injection, the working distance and the energy coupled in the higherorder modes. The energy balance is performed on the basis of the known ablation threshold of the material. Finally, the dependence between the etching depth and the number of pulses is studied. Saturation is observed probably due to a redeposition of the etched material, showing that a higher pulse energy is required for deeper etchings.

Mestrado em Engenharia Mecânica Nos ultimos anos, o uso da bra otica cresceu consideravelmente, sendo os sensores uma das suas maiores aplica c~oes. Esta tecnologia tem diversas vantagens sobre os sensores convencionais tais como: imunidade a interfer^ encias eletromagn eticas, biocompatibilidade e elevada sensibilidade. No entanto, h a interesse cient co e industrial em melhorar o seu desempenho (sensibilidade, resolu c~ao do sensor e gama de trabalho), sendo o revestimento da bra otica com diversos materiais um dos procedimentos que poder a ser usado para alcan car esse objectivo. O oxido de grafeno e um derivado do carbono que resulta da exfolia c~ao da gra te. Este nanomaterial consiste em folhas semelhantes as do grafeno mas possui grupos funcionais de oxig enio que podem reagir f sica ou quimicamente com diversas esp ecies. No ^ambito desta disserta c~ao foram revestidas bras oticas com oxido de grafeno atrav es da deposi c~ao por camadas. Nos revestimentos variou-se o processo de deposi c~ao e o n umero de camadas. A caracteriza c~ao foi feita atrav es de espectroscopia de Raman, microscopia electr onica de varrimento e microscopia de for ca at omica. Para averiguar a integridade dos revestimentos imersos em solu c~ao aquosa, foram realizados testes de lix via c~ao. Os resultados da caracteriza c~ao dos revestimentos con rmam a presen ca de oxido de grafeno na superf cie da bra otica. Depois de garantir a qualidade dos revestimentos procedeu-se ao desenvolvimento e caracteriza c~ao dos sensores baseados em bra otica com revestimentos de oxido de grafeno. Foram testadas duas con gura c~oes diferentes baseadas em redes de Bragg uniformes e inclinadas. Os sensores foram testados sem e com revestimento a varia c~oes de ndice de refra c~ao, variando o procedimento de deposi c~ao do oxido de grafeno e o n umero de camadas. A corros~ao do ferro e um dos maiores problemas enfrentados pelos engenheiros. E a degrada c~ao gradual dos metais provocada por rea c~oes qu micas resultantes da intera c~ao do metal e o meio ambiente. Neste trabalho pretendeu-se, ainda, investigar a possibilidade do oxido de grafeno estabelecer liga c~oes qu micas com o ferro, e assim permitir detectar o fen omeno da corros~ao. Neste caso os sensores foram testados em solu c~oes de nitrato de ferro(III). Veri cou-se que h a altera c~ao das caracteristicas dos espetros das redes de Bragg quando s~ao imersos em diferentes solu c~oes, no entanto os resultados n~ao s~ao muito conclusivos quanto as diferen cas entre os procedimentos de deposi c~ao e ao n umero de camadas. In the last years, the use of optical bers has grown considerably, being sensors one of the biggest applications. This technology has several advantages over conventional sensor such as: immunity to electromagnetic interferences, biocompatibility and high sensitivity. However, there is a scienti c and industrial interest to improve the sensor performance (sensitivity, resolution and working range). Coating the optical ber sensor with di erent materials is one proceeding that can be used to achieve this goal. Graphene oxide is a carbon derivative which results from the exfoliation of graphite. This nanomaterial consists in graphene like sheets with oxygen functional groups that can react physicaly or chemically with di erent species. In this work several optical bers samples were coated with GO through the layer by layer method. Two di erent proceedings were tested as the in uence of the number of of graphene oxide layers. The coating characterization was made through Raman spectroscopy, scanning electron microscopy and atomic force microscopy. To test the integrity of the coatings immersed in aqueous solutions, a leaching test was carried out. The results of the characterization con rm the presence of graphene oxide in the optical ber surface. After ensuring the quality of the graphene oxide coatings, it was carried out the development and characterization of optical ber based sensors with graphene oxide coatings. Were tested two di erent sensor con gurations, one based in uniform Bragg gratings and the other in tilted Bragg gratings. The sensors were tested without and with coating to refractive index variations, changing the proceeding to deposit the graphene oxide and the number of layers. Iron corrosion is one of the biggest problems faced by engineers. It is the gradual degradation of the metal by chemical reactions produced by the interactions of the metal with the environment. In this work, it was studied the possibility of the graphene oxide interact with the iron ion in order to detect the corrosion phenomenon. In this case, the sensors were tested in iron(III) nitrate solutions. It was veri ed that there are alterations of the Bragg gratings spectra characteristics when they were immersed in di erent solutions, however the results are not conclusive concerning the in uence of the coating proceeding used and the in uence of the number of layers.

Mestrado em Engenharia Mecânica Submitted by Cristina Santos (cmaria@ua.pt) on 2017-02-21T16:10:21Z No. of bitstreams: 1 Dissertação_EdgarMartins.pdf: 12195832 bytes, checksum: 5e86e7684d6a74df4b2ae728b3d3d262 (MD5) Made available in DSpace on 2017-02-21T16:10:22Z (GMT). No. of bitstreams: 1 Dissertação_EdgarMartins.pdf: 12195832 bytes, checksum: 5e86e7684d6a74df4b2ae728b3d3d262 (MD5) Previous issue date: 2016