Abstract: High intensity femtosecond (fs) lasers have become an affordable and versatile tool to modify all kinds of materials and to characterize the induced modifications. These capabilities derive from the ultrafast interaction between the electromagnetic field and matter, which distinguishes this kind of laser from all others. In the time frame of the fs pulses, the predominant interaction with the matter occurs through electron excitation, and several processes take place with increasing intensity: nonlinear excitation, ionization and recombination, which occur in a non-selective way due to the short time of interaction. The after-pulse evolution is due mainly to electrostatic interactions, involving the relaxation of the electrons energy to and between atoms. Coulomb and phase explosions, for example, are predominant for intensities in the range of TW/cm2 to PW/cm2, and they ablate all material (metals, polymers, dielectrics, etc) with a very high precision due to the small heat effect zone of these interactions. At the High Intensity Ultrashort Pulses Lasers Laboratory at IPEN we daily generate femtosecond pulses with intensities of 100 TW/cm2 and above. In this work we describe results obtained by our group using ultrashort pulses from Ti:Sapphire lasers covering the creation of color centers in crystals, glasses and polymers, the inscription of waveguides and the creation of surface structures that can range from the colorization of metals to the manufacture of microfluidic circuits, as well as the removal of burned tissue from living organisms. The pulses can also be used to study how defects pileup during the etching of a solid by superimposing pulses, and how the ablation process is affected by the incubation. At higher intensities the pulses can modify materials, and we present the controlled synthesis of nanoparticles, and the modification of graphite into diamond by the shockwaves generated during the ablation as a product of an evolving underdense plasma that generates local high temperatures and pressures. Also, the materials characterization is possible by spectroscopic measurements of the plasma elements atomic lines. Furthermore, we present results on the production of radiation on the deep ultraviolet by generation of harmonics of the laser interaction with gases, and also our recent efforts towards the acceleration of electrons by ultrashort laser pulses. Both the harmonics and electrons ultrafast beams could be used to modify and characterize materials by pump-probe, spectroscopic and diffraction measurements.

SAMAD, R.E.; MALDONADO, E.P.; COURROL, L.C.; ROSSI, W. de; BALDOCHI, S.L.; ZEZELL, D.M.; VIEIRA JUNIOR, N.D. High intensity femtosecond lasers at IPEN: tools for modification and characterization of materials. In: INTERNATIONAL CONFERENCE ON OPTICAL, OPTOELECTRONIC AND PHOTONIC MATERIALS AND APPLICATIONS, 8th, August 26-31, 2018, Maresias, SP. Abstract... 2018. Disponível em: http://repositorio.ipen.br/handle/123456789/29814. Acesso em: $DATA.

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Abstract: Este trabalho busca comprovar a aplicabilidade da tomografia computadorizada industrial (TCI), no controle dimensional de peças plásticas, por meio do estudo de otimização de parâmetros de máquina (tensão, corrente, spot size, número de projeções) e parâmetros de software (escala de cinza, reconstrução matemática, número de polígonos) para obtenção de resultados confiáveis e com boa resolução da nuvem de pontos. O objeto de análise foi um padrão de baquelite com geometrias retangulares e circulares fornecido por uma empresa alemã usuária da tecnologia. Os resultados da TCI foram comparados com resultados obtidos por máquina de medir por coordenadas (MMC) e medidor de altura. Para otimização dos parâmetros de escaneamento, os detalhes do padrão com características dimensionais menores que 2 mm foram analisados visualmente, pois estes estão sujeitos a maior perda de definição devido à resolução da nuvem de pontos. Com base nas comparações, notou-se que o parâmetro de maior influência é o voxel size que é função da tensão e da corrente, deste modo, concluiu-se que o voxel deveria ser da ordem de 40 μm. Embora os métodos de controle dimensional utilizados na comparação possuam diferentes incertezas de medição, que é caracterizada como erro aleatório, as dimensões das características avaliadas por TCI apresentaram desvios de aproximadamente 18 μm em relação aos resultados da MMC e medidor altura, estando acima dos valores de incerteza dos métodos, porém relativamente pequenos em relação as variações esperadas em peças fabricadas pelo processo de injeção. Concluiu-se então, que a TCI é um método confiável para controle dimensional de peças plásticas, permitindo resultados confiáveis e semelhantes aos métodos tradicionais de medição, além de possibilitar a análise de detalhes complexos e de difícil acesso a outros métodos, como por exemplo, pequenos furos e canais. Outro benefício é a redução de fontes de erro de medição, como por exemplo, pressão de apalpação, existente em métodos táteis e consideravelmente influente em peças plásticas de pequenas espessuras. A TCI pode ainda oferecer soluções para análise falhas de preenchimento podendo ser uma importante ferramenta para otimização de processos de injeção.

Palavras-Chave: optimization; computerized tomography; polymers; mathematical models; injection; uses; size; control

VIEIRA, A.; CARDOSO, C.; FELIX, J.B.; ROSSI, W. de; MONTEIRO, W.A. Otimização de parâmetros de tomografia computadorizada industrial para comparação entre peças de polímero e modelo matemático. In: CONGRESSO BRASILTEC & VINILTEC, 3., 8-9 de novembro, 2016, São Paulo, SP. Resumo... 2016. Disponível em: http://repositorio.ipen.br/handle/123456789/26987. Acesso em: $DATA.

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Abstract: Recently, rare earth doped nanocrystals received great attention due to their application in high-resolution panels, integrated optical systems and biological labeling. For efficient application of such materials, it is important that they can be produced in a reproducible way. The controlled synthesis of nanoparticles with uniform size, shape, structure and rare earth doping became of fundamental importance once the final properties are directly related to these parameters [1]. The NaYF4 is a very efficient host matrix for trivalent rare earth ions such as Yb/Er and Yb/Tm for upconversion systems. This fluoride crystallize in different dimensions and shapes in both its cubic and hexagonal phases. There are several synthetic processes already reported in the literature for production of this material, involving different chemical routes and processing from organic and inorganic compounds, however, the reproducibility of these processes are not always achieved. The objective of this work is to study different process for preparation of NaYF4:Yb:Er up conversion fluorides nanoparticles aiming a reproducible form to obtain these nanocrystals with well-defined size, shape and structure targeting biological and medical applications. Two production process are under study: (1) NaYF4 co-doped with Yb3+/Er3+ obtained by co-precipitation with different fluorinating compounds and, (2) NaYF4 co-doped with Yb3+/Er3+ obtained by micro-flow reaction using a microchannel and a micro capillary system. The microfluidic circuit was designed and fabricated at the Center for Lasers and Applications at IPEN. The micro capillary system was a commercial Asia flow chemistry modules from Syrris Co. Rietveld analysis of X-ray data showed that NaYF4:10%Yb3+/0,5%Er3+ were obtained by the coprecipitation method with cubic phase, presenting crystallite size in the range of 70 nm (Fig 1a). Routes using different fluorine sources were tested, and the best results were obtained from the addition of a NaF excess in the starting compounds. Before the study of the synthesis process, the ideal microchannel architecture for the flow chemical reactions has to be defined. The microfluidic system designed at IPEN (Fig1b.) is a two-stage microfluidic reactor: in the first stage, the product stream (NaF solution) is combined with the second precursor stream (RECl3 solution, were RE = rare earth). In the second stage the compounds flow through a heated zone (temperature range of 70 - 100ºC). The main compounds are guided through the system with two syringes, with flow controlled by the applied pressure (electronic controlled). Preliminary experiments are under way to analyze injection flow rates of the components, aiming to define the residence rate and temperature for desired nanoparticles production. With the Asia flow chemistry modules different experiments were performed with flows in the range of 100 – 600 μL/min, for NaF and RECl3 solutions, at temperature of 125°C. No chemical reaction were observed between fluorides and the microcircuit materials. The obtained material are under characterization to determine the efficiency of the experimental conditions adopted, in the size and phase of obtained NCs. Other experiments are in progress.

SILVA, T.F.A. da; COSTA, C.H.; VIANNA JUNIOR, A.S.; ROSSI, W. de; MAZZOCCHI, V.L.; BALDOCHI, S.L. Study of different production processes of doped rare earth fluorides nanoparticles: co-precipitation and microfluidics. In: INTERNATIONAL CONFERENCE OF NANOPHOTONICS, 10th, July 02-05, 2017, Recife, PE. Abstract... 2017. p. 51-51. Disponível em: http://repositorio.ipen.br/handle/123456789/27940. Acesso em: $DATA.

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