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The applications of femtosecond lasers (1 fs = 10-15s) for machining and surface treatment are being researched for a few decades, and among its advantages are the virtual absence of thermal processes during ablation, resulting in spatial accuracy and the indifference of physical characteristics of the material under treatment (metal or dielectric). The virtual absence of thermal effects in the ablation process with ultrashort pulses implies the possibility of producing machined structures with dimensions close to the diffraction limit for the laser wavelength used. For this, we must use focusing lenses with very short focal length and high numerical aperture. Thus, the precise and dynamic control of the overlap of the focal plane with a surface treatment is crucial. Changes of some tens of microns in the relative position of the surface treated, either by moving the sample or by its own relief characteristics, are often sufficient to significantly impair the accuracy of machining. It is proposed in this design the development of an interferometry system that takes advantage of the inherent characteristics of fs laser for evaluation of the focal position with an accuracy of a few microns, a technique based on low coherence interferometry. This approach has advantages over commercial systems currently used, which are sensitive only to metallic surfaces. To this development will need further scientific studies in order to assess possible distortions promoted by the formation of plasma in ablation process and also an exploration of the source region of reflection in laser-sample interaction At the end of the project a machining system will be mounted with dynamic adjustment of focus, which will be evaluated in different circumstances and with different types of samples. (AU)

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Scientific publications
(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)
RAELE, MARCUS PAULO; DE PRETTO, LUCAS RAMOS; DE ROSSI, WAGNER; VIEIRA, JR., NILSON DIAS; SAMAD, RICARDO ELGUL. Focus Tracking System for Femtosecond Laser Machining using Low Coherence Interferometry. SCIENTIFIC REPORTS, v. 9, MAR 12 2019. Web of Science Citations: 0.
RAELE, MARCUS PAULO; DE PRETTO, LUCAS RAMOS; ZEZELL, DENISE MARIA. Soldering mask laser removal from printed circuit boards aiming copper recycling. WASTE MANAGEMENT, v. 68, p. 475-481, OCT 2017. Web of Science Citations: 5.

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