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The potential application of metallic nanoparticles had been attracting attention and interest from different areas of academia and industry. The nanoparticles properties and applications depend heavily on their dimension and shape, thus special interest is aimed to controlling the nanoparticles sizes. Ultrashort laser pulses are known to change metallic nanoparticles characteristics, but the interaction mechanism is still not completely understood. In this work we reduced the dimension of silver nanoparticles with ultrashort pulses and demonstrated that there is a dependence of the particles size on the second order dispersion introduced in the pulses, which became smaller as the dispersion becomes more negative. Based on the results, we propose that the Coulomb explosion that reduces the nanoparticles size is predominantly initiated by multiphotonic ionization for the intensities used (1014 W/cm2).

We review the fundamentals of electron beam generation in self-modulated laser wakefield acceleration (SM-LWFA) using laser pulses with peak powers on the TW and sub-TW scale. The results of several new particle-in-cell simulations for λ = 0.8 µm and a thin H2 gas target are shown. By scanning the peak gas density and peak power values of the incident laser, we discuss the resulting acceleration processes, as well as the characteristics of the electron beams generated for different conditions. Our approach provides a method to optimize these beams with lasers operating at kHz repetition rates.

Electron beams generated by laser wakefield acceleration can induce a photoneutron reaction to convert 100Mo into 99Mo. Multi-pC, several-MeV electron beams, obtained from particle-in-cell simulations, could generate bremsstrahlung gamma photons within the absorption region of the photonuclear reaction. The efficiency of this process is estimated for a laser accelerator operating at kHz repetition rate in the self-modulated regime. The electron beam kinetic energy must be improved to 40MeV. To meet the typical consumption of 99Mo per patient within its decay timescale, this efficiency must be increased by three orders of magnitude.

This work reports the development of a modified Mach-Zehnder interferometer aimed at determining the density of gas targets and laser generated plasmas, in time and space. This interferometer will compose our laboratory implementations for laser wakefield acceleration, allowing the characterizations of gas jet profiles generated by submillimeter nozzles. The technique also allows us to estimate the temporal evolution of the plasma density.

Ultrashort laser pulses interact with matter in unique, nonselective ways, due to electronic direct excitation in an ultrafast time scale. Additionally, these pulses can cover peak powers from kW to PW, allowing its use to induce from nonlinear optics up to relativistic phenomena. Here we present a quick overview of the important processes induced in matter by high-intensity ultrashort pulses, and describe results obtained in our laboratory, including our most recent goal of accelerating electrons with ultrashort pulses for practical applications.

An analytical formulation of a multi-kilowatt ytterbium-doped double-cladding tandem-pumped fiber amplifier was developed and is reported in this paper. The model consists of a system including the laser rate, pumping and seed power equations. The model was validated by describing a fiber amplifier behavior with a 5.986kW, 1018nm pumping and a signal seed of 75W, 1080nm, yielding a maximum power output of 5.448kW, with an efficiency of 91.1%. The thermal equations are solved for the temperature distribution along the fiber with a maximum temperature of 43.24°C, when the convective coefficient of 4000W. m-2. K−1 is used.

This work reports the development and experimental implementation of a methodology for manufacturing submillimetric de Laval nozzles by ultrashort laser pulses micromachining by trepanning. The use of a ceramic substrate resulted in the fabrication of nozzles with high circularity and low roughness, which should generate high-quality gas targets for accelerating electrons with ultrashort laser pulses.

An analytical formulation and modeling of an optical fiber Bragg gratings has been developed and is reported in this paper. Supported by the coupled-mode theory and considering that the mode fields of the unperturbed waveguide remain unchanged in the presence of weak perturbations, it is possible to obtain first-order differential equations that have solutions for some types of periodic perturbations. Finally, the model is applied to analyze the influence of structural parameters of fiber gratings, such as length, period and refractive index modulation on its reflectivity and bandwidth.

This work reports a theoretical and experimental study of supersonic gas jets to be used as targets in laser wakefield acceleration. A comparison between theoretical and experimental results ismade in order to estimate the results of a de Laval nozzle manufactured in our laboratory, used to produce a N 2 gas target. The comparison between the results shows that Computational Fluid Dynamicssimulations are able todescribe the phenomena of the supersonic gas jet.

An analytical investigation of the refractive index behavior of an ytterbium-doped optical fiber silica glass as a function of the core-clad temperature, upper-level population laser density, and pumping signal intensity is presented in this paper. For the substantiation of the investigation, three fundamental expressions were used, which describe the changes in the refractive index due to these physical phenomena in the laser medium. The model was evaluated considering a 500 W steady state fiber laser, operating in a two-end pumped configuration.

In this work, we investigate a pedestal tantalum oxide (Ta

The present study investigates the effect of texturing the rake face of uncoated cemented tungsten carbide tools by ultrashort laser pulses for tribological improvement. In this sense, four parallel micro-groove texturing patterns were created on the rake face of the cutting tools, beginning at a variable distance from the cutting edge. The pitch between grooves was also varied. Friction force, machining force, chip features, and surface roughness were evaluated from semi-orthogonal dry turning in the reference (non-textured) and textured tools. The results showed friction force reduction by nearly 40%; chip deformation decrease around 21%; machining force reduction by 20%; and surface roughness by 46 and 28% for Ra and Rz, respectively, for the best texturing pattern.

Silver nanoparticles exhibit a powerful antimicrobial action showing a pronounced potential to be widely used against drug resistance bacteria. The present work describes the optical properties and antimicrobial effect of silver nanoparticles produced by femtosecond laser photoreduction of AgNO3 in the presence of tryptophan water solution. The advantages of this method are the absence of hazardous chemical reducing agents in the solution, and the versatile dimensional control achieved. The synthesized silver nanoparticles were characterized by absorption and fluorescence spectroscopy and their antibacterial activity were determined by monitoring the cell viability of Escherichia coli. The effects of the silver nanoparticles concentration and laser parameters (exposure time and pulse energy), on the formation of the nanoparticles, and its influence on the bacteria growth inhibition were studied. The prepared silver nanoparticles exhibited suitable antimicrobial properties. The results demonstrated that the nanoparticles concentration plays an important role in their bactericidal efficacy. The increase in the laser energy caused an increase in E. coli growth inhibition. Irradiations with energies around 300 μJ for 60 min presented high antimicrobial activity due to the presence of kynurenine, sub product of tryptophan photolysis. The first-time formation mechanism of tryptophan silver nanoparticles in high optical intensities was also discussed.

Meat quality is normally defined by a combination of factors such as visual appearance, smell, firmness, succulence, tenderness, and flavor. Contamination of poultry meat with pathogens remains an important public health issue since it can cause illnesses due to negligence in handling, cooking or post-cooking storage. Conventionally, meat quality tests are based on visual evaluation or chemical analysis, which have the disadvantages of being subjective and time-consuming. To improve the biological contamination detection accuracy and productivity, the evaluation of porphyrin contents in meat by fluorescence spectroscopy is proposed, considering that most microorganisms and animal cells excrete porphyrins. For this purpose, chicken meat was cut into small pieces and separated in three groups: a control group where the meat was conserved under refrigeration, and two experimental groups in which the pieces were kept for 24 and 30 h at room temperature. Porphyrin was extracted from the meat samples and the fluorescence was measured in the range 550–750 nm, under excitation around 400 nm. The fluorescence lifetime was also studied. To ensure porphyrin synthesis, a concentration of 9.3 mM of δ-Aminolevulinic acid (ALA) was added to each sample, 2 h before porphyrin extraction. The results show that, in meat kept at room temperature and incubated with ALA, the porphyrin fluorescence increased, and a short-lived component was enhanced due to the action of microorganisms, indicating a potential new method to test meat quality.

We evaluate the results of self-modulated, laser wakefield acceleration of electrons in homogeneous, 150-μm-thick hydrogen gas target, simulated using the spectral particle-in-cell algorithm FBPIC. Considering a single 2-TW laser pulse at 800-nm, which generates ionization and plasma displacement at relativistic intensities, we discuss the resultant wakefield phases, wave-breaking, and the ejected electron bunch properties: charge, length, divergence and energy, also comparing with experimental results.

This work reports the generation of Below Threshold Harmonics generated in Argon by ultrashort laser pulses. The 3rd, 5th, 7th and 9th harmonics of the laser were generated in the UV and VUV regions, and the frequency conversion occurred in flowing gas in a glass nozzle into a vacuum chamber. The harmonics generated show a blue-shift and an efficiency that depend on the laser pulses intensity and also on the gas pressure. These parameters determine the phase-matching condition, which governs the energy conversion from the laser into the harmonics, and this study shows that is possible to tune the harmonics intensity and wavelength, providing a versatile light source.

Laser particle acceleration is now in a new trend due to an enormous worldwide effort to increase the peak power of femtosecond lasers, as well as increasing their average power in order to make them useful for applications. The leading example is the Extreme Light Infrastructure in Europe, which has led to the establishment of three large research facilities in the Czech Republic, Romania and Hungary that host some of the most powerful lasers worldwide (above PW peak power). This action is now being followed by the USA LaserNetUS initiative, that comprises all the big laser facilities in US, and similar efforts also happen in Asia. We are starting a program to establish a laser accelerator facility in Brazil, aiming to produce radiation (electrons, protons and X rays) to be used in medical applications, like X ray and electron therapy, nuclear reactions and, eventually, protontherapy.

This study was done to evaluate whether the irradiation of dentine with ultrashort laser pulses prior to adhesive procedures contributes to increase the adhesive resistance to microtraction essays. Twenty-four human teeth (third molars) were used, divided into 4 groups (n=6): standard adhesive procedures with etch-rinse adhesive were used in the control group, and in the experimental groups, the dentin was irradiated by 25 fs pulses prior to the adhesive procedures, with varying fluences. One tooth from each group was used to evaluate its surface roughness. After 24h, the teeth were sectioned with perpendicular cuts, producing toothpicks that were submitted to the microtraction test. The results showed that the groups irradiated with fluences under 4 J/cm² presented similar results among themselves, comparable to the control group, while the group irradiated with 8 J/cm² showed lower adhesive strength. We propose that the adhesive strength and surface roughness reduction resulting from the fluence increase is probably related to the shielding arising from an electron plasma formation during the ablation, decreasing the material removal efficiency. Nevertheless, the lower energy densities did not affect the adhesiveness, maintaining values similar to the control.

The ablation threshold for ultrashort pulses of common optical materials (BK7 glass, Sapphire and Fused Silica), was measured using the D-Scan technique, for positive and negative dispersions covering pulse durations from 30 fs to 100 fs. We observed that the ablation threshold for a single shot and at saturation increase with the pulse duration and the material bandgap, and also that defects which decrease the threshold values accumulate faster as the material bandgap increases.

We report the fabrication and characterization of double line waveguides directly written in tellurite and germanate glasses using a femtosecond laser delivering 30 μJ, 80 fs pulses at 4 kHz repetition rate. The double line waveguides produced presented internal losses inferior to 2.0 dB/cm. The output mode profile and the M 2 measurements indicate multimodal guiding behavior. A better beam quality for the GeO 2 – PbO waveguide was observed when compared with TeO 2 – ZnO glass. Raman spectroscopy of the waveguides showed structural modification of the glassy network and indicates that a negative refractive index modification occurs at the focus of the laser beam, therefore allowing for light guiding in between two closely spaced laser written lines. The refractive index change at 632 nm is around 10 −4 , and the structural changes in the laser focal region of the writing, evaluated by Raman spectroscopy, corroborated our findings that these materials are potential candidates for optical waveguides and passive components. To the best of our knowledge, the two double line configuration demonstrated in the present work was not reported before for germanate or tellurite glasses.

This work presents a study on laser wakefield electron acceleration in the self-modulated regime (SM-LWFA) using 50-fs laser pulses with energy on the mJ scale, at λ = 0.8 µm, impinging on a thin H2 gas jet. Particle-in-cell simulations were performed using laser peak powers ranging from sub-terawatt to a few terawatts and plasma densities varying from the relativistic self-focusing threshold up to values close to the critical density. The differences in the obtained acceleration processes are discussed. Results show that bunched electron beams with full charge on the nC scale and kinetic energy in the MeV range can be produced and configurations with peak density in the range 0.5–5 × 1020 atoms/cm3 generate electrons with maximum energies. In this range, some simulations generated quasimonoenergetic bunches with ∼0.5% of the total accelerated charge and we show that the beam characteristics, process dynamics, and operational parameters are close to those expected for the blowout regime. The configurations that led to quasimonoenergetic bunches from the sub-TW SM-LWFA regime allow the use of laser systems with repetition rates in the kHz range, which can be beneficial for practical applications.

In this work the diffusion of mercury and other elements from amalgam tooth restorations through the surrounding dental tissue (dentin) was evaluated using femtosecond laser-induced breakdown spectroscopy (fs-LIBS). To achieve this, seven deciduous and eight permanent extracted human molar teeth with occlusal amalgam restorations were half-sectioned and analyzed using pulses from a femtosecond laser. The measurements were performed from the amalgam restoration along the amalgam/dentin interface to the apical direction. It was possible to observe the presence of metallic elements (silver, mercury, copper and tin) emission lines, as well as dental constituent ones, providing fingerprints of each material and comparable data for checking the consistence of the results. It was also shown that the elements penetration depth values in each tooth are usually similar and consistent, for both deciduous and permanent teeth, indicating that all the metals diffuse into the dentin by the same mechanism. We propose that this diffusion mechanism is mainly through liquid dragging inside the dentin tubules. The mercury diffused further in permanent teeth than in deciduous teeth, probably due to the longer diffusion times due to the age of the restorations. It was possible to conclude that the proposed femtosecond-LIBS system can detect the presence of metals in the dental tissue, among the tooth constituent elements, and map the distribution of endogenous and exogenous chemical elements, with a spatial resolution that can be brought under 100 µm.

In this work, the non-linear refractive index (n 2 ) of silicon oxynitride (SiO x N y ) is determined, obtaining a value for this material of n 2 = 2.11×10-19 m2/W. The results demonstrate that this material has interesting properties for the development of non-linear optical devices. The paper presents in detail the waveguide fabrication process using the pedestal technique, which allows using different materials since it does not require etching to define the sidewalls of the waveguides. We show the results of the measurement of the n2 employing the non-linear optical phenomena of Self-Phase Modulation (SPM).

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.

This study investigated the production of boron films by femtosecond pulsed laser deposition (PLD) to be used as converters on bulk semiconductor neutron detectors. The ablation threshold of metallic boron was determined and the film growth was studied as a function of deposition time (5–90 min) and laser pulse energy (35–530 μJ). The films were characterized by scanning electron microscopy (SEM), revealing a flaky morphology, optical profilometry, which determined the films thicknesses (from 80 nm up to 4 μm), Ion Beam Analysis (IBA) that assessed their elemental composition and X-ray diffraction (XRD), which revealed an amorphous structure. In addition, a thermal load study was performed to evaluate the heat flux onto the substrate during deposition process. Stable boron films obtained show that the femtosecond PLD process is reliable and reproducible for the fabrication of thick boron coatings.

Made available in DSpace on 2020-12-12T01:10:01Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-01-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) In this work, we investigate a pedestal tantalum oxide (Ta2O5) material platform for integrated nonlinear optics (NLO). In order to achieve low propagation losses with this material, pedestal waveguides with Ta2O5 cores were designed. The nonlinear refractive index n2 of this new platform was obtained by measuring the amount of spectral broadening due to self-phase modulation (SPM) of 23 fs optical pulses at 785 nm propagating through the waveguides. In this manner, a nonlinear index of (5.8 ± 2.0) × 10−19 m2W−1 was found for this material, which is in good agreement with values reported in related works where strip waveguides were used for a similar purpose. Furthermore, due to the pedestal configuration, propagation losses as low as 1.6 dB·cm−1 for narrow waveguides and 0.1 dB·cm−1 for large waveguides were obtained. Finite element method (FEM) mode analysis was performed to calculate the mode characteristics, as well as the effective areas of the waveguides. The high nonlinear and linear refractive indices, wide bandgap and low propagation losses make this platform ideal for applications extending from the visible into the mid-IR regions of the optical spectrum. Due the large gap, Ta2O5 should have low two photon absorption at the near-IR as well. Polytechnic School University of São Paulo (USP) Center for Lasers and Applications IPEN-CNEN/SP Telecommunications Department São Paulo State University (UNESP) Telecommunications Department São Paulo State University (UNESP) CNPq: 305447/2017-3 CNPq: 32088/2018-0

This work reports development of glass nozzles by ultrashort laser pulses machining for studies of harmonic generation in gases. Those nozzles generated odd harmonics (3rd up to 25th) in UV and VUV regions.

Laser particle acceleration is a rapid growing field due to the compactness and smaller cost when compared to traditional accelerators, as well as the potential for new applications resulting from the unique characteristics of the beams generated. Frequently, laser acceleration techniques require laser intensities higher than 100’s of PW/cm2 and high-density gas targets, with specific profiles. In the effort to implement laser electron acceleration in our laboratories, we report the development of submillimetric, supersonic gas nozzles, the implementation of optical techniques for the determination of the gas jets density profiles, and the characterization of laser-induced plasmas obtained at laser intensities surpassing 1016 W/cm2. The characterization techniques employed include plasma spectroscopy, interferograms and Schlieren images.

This work reports studies on the generation of below threshold harmonics by ultrashort laser pulses in gas nozzles in vacuum. Odd harmonics of the laser, ranging from the 3rd up to the 9th, were generated in the UV and VUV regions, and the frequency conversion occurred in flowing gas. The harmonics were spectrally characterized, and the orders of the nonlinear processes were determined, showing that, for the higher order harmonics, competing processes decrease the energy coupling into the new frequencies. Also, the conversion efficiencies were estimated, showing that a few percent of the laser pulse energy are converted into the harmonics.

Silver nanoparticles (AgNPs) have been intensively studied for several purposes including therapeutic applications in cancer. When prepared with tryptophan and photoreduction, silver nanoparticles (TrpAgNPs) become an alternative to conventional anticancer drugs. In this study, the anticancer activity of synthesized TrpAgNPs against MCF-7 breast cancer cells was evaluated, and the inhibitory concentration (IC50) was found to be ~3.4 mg/mL. Since the protoporphyrin IX (PPIX) concentrations in tumor cells are elevate compared to normal cells, the PPIX-TrpAgNP interaction was studied to investigate if it could contribute for cell apoptosis. The investigation was performed using PPIX solution (0.9 μg/mL) with different TrpAgNP concentrations (from 0 to 13 mg/mL). PPIX was characterized by UV-Vis spectroscopy, steady-state and time-resolved fluorescence spectroscopy. The results have shown that the presence of spherical TrpAgNps with 16-nm diameter quench the PPIX fluorescence intensity. This quenching is strongly dependent on the concentration of the TrpAgNPs, and it is caused by a combination of a static and a dynamic process. The chemical binding leads to oxidation of tryptophan and formation of kynurenine, observed in the emission spectra around 470 nm. The strong reduction of the PPIX fluorescence decay lifetime with nanoparticle increasing concentration confirms the quenching processes due to charge transfer from the excited PPIX states to the resonant silver states. The present study confirms the anticancer activity of TrpAgNPs on the human breast cancer cell line (MCF-7) in vitro and indicates that PPIX-AgNP interaction could contribute with MCF-7 apoptosis.

Dimensional 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.

The authors report the fabrication and characterization of passive waveguides in GeO2–PbO and TeO2–ZnO glasses written with a femtosecond laser delivering pulses with 3μJ, 30μJ and 80fs at 4kHz repetition rate. Permanent refractive index change at the focus of the laser beam was obtained and waveguides were formed by two closely spaced laser written lines, where the light guiding occurs between them. The refractive index change at 632 nm is around 10-4 . The value of the propagation losses was around 2.0 dB/cm. The output mode profiles indicate multimodal guiding behavior. Raman measurements show structural modification of the glassy network. The results show that these materials are potential candidates for passive waveguides applications as low-loss optical components.

The backscattered light originated when machining with femtosecond laser pulses can be used to accurately measure the processed surface position through an interferometer, as recently demonstrated by our group, in a setup that uses the same laser beam for ablation and inspection. The present work explores the characteristics of the laser light reflected by the target and its interaction with the resulting plasma to better understand its propagation physics and to improve the dynamic focusing system. The origin of this returning radiation was studied and has been traced, mainly, from the peripheral area of the focal spot (doughnut-like). By means of a Mach-Zehnder setup, the interferometric pattern was measured and analyzed aiming to access the influences of the plasma on the laser beam properties, and therefore on the retrieved information. Finally, the wavefront of the laser that creates and propagates through the plasma was characterized using a Shack-Hartmann sensor.

Boron thin films were produced using femtosecond pulsed laser deposition aiming at the development of a neutron detector. As neutrons have no charge, in order to detect this particle converter materials are applied, promoting nuclear reactions that result in the emission of charged particles, allowing the neutrons presence to be indirectly inferred. Among the possible conversion materials, 10 B has a considerable cross section for thermal neutrons and accessible cost. Furthermore, the nuclear reaction produces easily detectable alpha particles, making it a rational option to develop a low cost and portable neutron detector. The boron ablation threshold fluence has been measured by the Diagonal Scan (Dscan) technique that resulted in the minimum laser energy value of 17.7 (6) μJ and fluence of 5.63(19) J/cm 2 . Boron deposition was performed varying the pulse energy and deposition duration. The growth rate, morphological and physical aspects of the boron pulsed laser deposition were characterized by a Scanning Electron Microscope and an optical profilometer. The films surfaces have a flaky aspect with eventual droplets which had decayed overtime to a more smooth surface. The studied parameters allowed producing a boron coating with the optimal thickness in order to minimize self-absorption effect in the film, thus increasing efficiency.

Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) In this work, fluorescence lifetime has been used to analyze protoporphyrin IX (PPIX) extracted from blood for diagnosing atherosclerosis. A total of 10 adult white male rabbits (New Zealand) were divided into the control group (CG), with a normal diet, and the experimental group (EG), subjected to a diet containing 1% cholesterol. Blood samples were collected from the animals, and protoporphyrin IX was extracted from the blood using acetone. The PPIX fluorescence lifetime (PPIXFL) was measured using time-correlated single photon counting, after excitation at 403 nm from a pulsed laser diode. It was found that the PPIX emission intensity was enhanced in the animals that had received a hypercholesterolemic diet. The CG and EG animal's fluorescence decays were fitted by three exponentials and the mean lifetimes were 4.0 ns and 9.5 ns, respectively. This lifetime dependence resulted in a calibration curve that allows the determination of the PPIX concentration with a temporal measurement. The obtained results show that fluorescence lifetime can potentially be used as a noninvasive, simple, rapid, and sensitive tool in atherosclerosis diagnosis. IPEN CNEN SP, Sao Paulo, SP, Brazil Univ Fed Sao Paulo, Dept Fis, Diadema, SP, Brazil Univ Fed Sao Paulo, Dept Fis, Diadema, SP, Brazil FAPESP: 2014/06960-9 Web of Science

Taking advantage of the inherent characteristics of femtosecond laser used for machining, we developed an interferometric system able to evaluate and correct the focal position with an accuracy of a few microns, implementing a technique based on low coherence interferometry. This approach measures at the exact spot that the laser is machining, in real time, and is sensitive to any sample that acts as a scatterer to the wavelength in use. The experimental evaluation was divided in two steps: in the first a system based on a superluminescent LED was mounted to check the viability and develop the controlling software; in the second part a setup was mounted employing a femtosecond laser, and several kinds of samples using the active focus control, among which the results obtained with glass sample and a bovine tooth are meticulously described in this paper. The system was able to improve the performance in both samples, keeping them in the confocal region for an extended positioning range, resulting in better engraving by the laser.

Thousands of people die every year from burn injuries. The aim of this study is to evaluate the feasibility of high intensity femtosecond lasers as an auxiliary treatment of skin burns. We used an in vivo animal model and monitored the healing process using 4 different imaging modalities: histology, Optical Coherence Tomography (OCT), Second Harmonic Generation (SHG), and Fourier Transform Infrared (FTIR) spectroscopy. 3 dorsal areas of 20 anesthetized Wistar rats were burned by water vapor exposure and subsequently treated either by classical surgical debridement, by laser ablation, or left without treatment. Skin burn tissues were non-invasively characterized by OCT images and biopsied for further histopathology analysis, SHG imaging and FTIR spectroscopy at 3, 5, 7 and 14 days after burn. The laser protocol was found as efficient as the classical treatment for promoting the healing process. The study concludes to the validation of femtosecond ultra-short pulses laser treatment for skinburns, with the advantage of minimizing operatory trauma.