LUCAS RAMOS DE PRETTO
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Artigo IPEN-doc 25775 Focus tracking system for femtosecond laser machining using low coherence interferometry2019 - RAELE, MARCUS P.; DE PRETTO, LUCAS R.; ROSSI, WAGNER de; VIEIRA JUNIOR, NILSON D.; SAMAD, RICARDO E.We designed a real time, single-laser focus tracking system using low coherence properties of the machining femtosecond laser itself in order to monitor and correct the sample position relative to the focal plane. Using a Michelson Interferometer, the system collects data arising from part of the beam backscattered at the ablation spot. The data is analyzed by a custom software for position correction (employing an XYZ automated translation stage). With the focus tracking enabled we were able to etch channels with a stable cross-section profile on a bovine tooth with relief amplitude tens of times greater than the Rayleigh length of the system, keeping the sample inside the confocal parameter during most of the processing time. Moreover, the system is also capable of monitoring crater depth evolution during the ablation process, allowing for material removal assessment.Artigo IPEN-doc 24779 Optical coherence tomography characterization of femtosecond laser manufactured microfluidic circuits2018 - PRETTO, LUCAS R. de; SAMAD, RICARDO E.; ROSSI, WAGNER de; FREITAS, ANDERSON Z. deDimensional characterization of microfluidic circuits were performed using three-dimensional models constructed from OCT images of such circuits. Were fabricated microchannels on the same BK7 glass plate, under different laser ablation conditions and substrate displacement velocity in relation to laser beam. Were used the following combination of energy, from 30 μJ to 60 μJ and velocity from 588 mm/min to 1176 mm/min, at 1 kHz laser repetition rate and 40 fs of pulse duration (FWHM). For OCT imaging we used an OCP930SR (Thorlabs System Inc) with 930 nm central wavelength, 6 μm of lateral and axial resolution, and image of 500 x 512 pixel corresponding to 2.0 mm x 1.6 mm of lateral and axial scans respectively at 8 frames per second. We also characterized devices like, micropumps, microvalves and microreactors. It was possible register the micropumps and valves in action in real time. Using the OCT images analyses was possible to select the best combination of laser pulse energy and substrate velocity. All the devices were made in raster protocol, where laser beam pass through the same path in a controlled number of times, and with each iteration more material is removed and deeper the channels remain. We found a deformation at the edge of fabricated structures, due to velocity reduction of substrate in relation to laser beam, which causes more laser pulses superposition in these regions, and more material is ablated. The technique was thus evaluated as a potential tool to aid in the inspection of microchannels.Artigo IPEN-doc 22984 Optical Coherence Tomography for blood glucose monitoring through signal attenuation2016 - PRETTO, LUCAS R. de; YOSHIMURA, TANIA M.; RIBEIRO, MARTHA S.; FREITAS, ANDERSON Z. deDevelopment of non-invasive techniques for glucose monitoring is crucial to improve glucose control and treatment adherence in patients with diabetes. Hereafter, Optical Coherence Tomography (OCT) may offer a good alternative for portable glucometers, since it uses light to probe samples. Changes in the object of interest can alter the intensity of light returning from the sample and, through it, one can estimate the sample's attenuation coefficient (μt) of light. In this work, we aimed to explore the behavior of μt of mouse’s blood under increasing glucose concentrations. Different samples were prepared in four glucose concentrations using a mixture of heparinized blood, phosphate buffer saline and glucose. Blood glucose concentrations were measured with a blood glucometer, for reference. We have also prepared other samples diluting the blood in isotonic saline solution to check the effect of a higher multiple-scattering component on the ability of the technique to differentiate glucose levels based on μt. The OCT system used was a commercial Spectral Radar OCT with 930 nm central wavelength and spectral bandwidth (FWHM) of 100 nm. The system proved to be sensitive for all blood glucose concentrations tested, with good correlations with the obtained attenuation coefficients. A linear tendency was observed, with an increase in attenuation with higher values of glucose. Statistical difference was observed between all groups (p<0.001). This work opens the possibility towards a non-invasive diagnostic modality using OCT for glycemic control, which eliminates the use of analytes and/or test strips, as in the case with commercially available glucometers.Artigo IPEN-doc 21368 New speckle analysis method for optical coherence tomography signal based on autocorrelation2015 - PRETTO, LUCAS R. de; NOGUEIRA, GESSE E.C.; FREITAS, ANDERSON Z.Artigo IPEN-doc 21366 New speckle analysis algorithm for flow visualization in optical coherence tomography images2015 - PRETTO, LUCAS R. de; NOGUEIRA, GESSE E.C.; FREITAS, ANDERSON Z.Artigo IPEN-doc 21365 Novo algoritmo para visualização de fluxo através do speckle presente em imagens de tomografia por coerência óptica2014 - PRETTO, L.R. de; NOGUEIRA, G.E.C.; FREITAS, A.Z.