A didactic sequence of elementary geometric optics Informed by history and philosophy of science

The concepts and instruments required for the teaching and learning of geometric optics are introduced in the didactic processwithout a proper didactic transposition. This claim is secured by the ample evidence of both wide- and deep-rooted alternative concepts on the topic. Didactic transposition is a theory that comes from a reflection on the teaching and learning process in mathematics but has been used in other disciplinary fields. It will be used in this work in order to clear up the main obstacles in the teachinglearning process of geometric optics. We proceed to argue that since Newton’s approach to optics, in his Book I of Opticks, is independent of the corpuscular or undulatory nature of light, it is the most suitable for a constructivist learning environment. However, Newton’s theory must be subject to a proper didactic transposition to help overcome the referred alternative concepts. Then is described our didactic transposition in order to create knowledge to be taught using a dialogical process between students’ previous knowledge, history of optics and the desired outcomes on geometrical optics in an elementary pre-service teacher training course. Finally, we use the scheme-facet structure of knowledge both to analyse and discuss our results as well as to illuminate shortcomings that must be addressed in our next stage of the inquiry.

Laser surfasse patterning using a Michelson interferometer and a femtosecond laser radiation

We report on a simple method to obtain surface gratings using a Michelson interferometer and femtosecond laser radiation. In the optical setup used, two parallel laser beams are generated using a beam splitter and then focused using the same focusing lens. An interference pattern is created in the focal plane of the focusing lens, which can be used to pattern the surface of materials. The main advantage of this method is that the optical paths difference of the interfering beams is independent of the distance between the beams. As a result, the fringes period can be varied without a need for major realignment of the optical system and the time coincidence between the interfering beams can be easily monitored. The potential of the method was demonstrated by patterning surface gratings with different periods on titanium surfaces in air.

Cidade digital

A Resolução do Conselho de Ministros n.º 120/2008, de 30 de Julho, definiu como prioridade estratégica para o País, no sector das comunicações electrónicas, a promoção do investimento em redes de nova geração. Com o objectivo de dar execução às orientações estratégicas estabelecidas, o Decreto -Lei n.º 123/2009, de 21 de Maio, veio estabelecer um conjunto de obrigações aplicáveis ao Estado, às Regiões Autónomas, às autarquias locais, empresas públicas, concessionárias e, genericamente, às entidades que detenham infra-estruturas que se integrem em domínio público, de forma a garantir a todas empresas de comunicações electrónicas, o acesso às infra-estruturas aptas ao alojamento de redes de comunicações electrónicas. Em Portugal, o caminho a ser traçado até as redes de nova geração passa pela, abertura eficaz e não discriminatória de todas as condutas e outras infra-estruturas aptas ao alojamento de redes de comunicações electrónicas, elaboração de regras técnicas aplicáveis às infra-estruturas de telecomunicações em loteamentos, urbanizações e conjuntos de edifícios, adopção de soluções que eliminem ou atenuem as barreiras verticais à instalação de fibra óptica e que evitem a monopolização do acesso aos edifícios pelo primeiro operador. Neste âmbito, excluem-se, pela sua especial natureza e fins a que estão afectas, as redes privativas dos órgãos políticos de soberania, do Ministério da Defesa Nacional, das forças e serviços de segurança, de emergência e de protecção civil. Assim, este trabalho visa apresentar procedimentos aplicáveis às infra-estruturas de telecomunicações para elaboração de um cadastro de todas as infra-estruturas, públicas e privadas, aptas ao alojamento de redes de comunicações electrónicas, e propor instruções técnicas para as condições e direitos de acesso, construção e intervenção sobre estas infra-estruturas.

Laser-assisted deposition of thin films from photoexcited vapour phases

Laser-assisted chemical vapour deposition (LCVD) has been extensively studied in the last two decades. A vast range of applications encompass various areas such as microelectronics, micromechanics, microelectromechanics and integrated optics, and a variety of metals, semiconductors and insulators have been grown by LCVD. In this article, we review briefly the LCVD process and present two case studies of thin film deposition related to laser thermal excitation (e.g., boron carbide) and non-thermal excitation (e.g., CrO(2)) of the gas phase.

Sub-micron structuring of silicon using femtosecond laser interferometry

We report the fabrication of planar sub-micron gratings in silicon with a period of 720 nm using a modified Michelson interferometer and femtosecond laser radiation. The gratings consist of alternated stripes of laser ablated and unmodified material. Ablated stripes are bordered by parallel ridges which protrude above the unmodified material. In the regions where ridges are formed, the laser radiation intensity is not sufficient to cause ablation. Nevertheless, melting and a significant temperature increase are expected, and ridges may be formed due to expansion of silicon during resolidification or silicon oxidation. These conclusions are consistent with the evolution of the stripes morphology as a function of the distance from the center of the grating. (C) 2013 Elsevier Ltd. All rights reserved.