ALLAN BERECZKI
13 resultados
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Artigo IPEN-doc 30184 Sub-nanosecond microchip oscillator for a MOPA system tailored for tattoo removal2023 - CATARINA, MARCUS V.; BERECZKI, ALLAN; WETTER, NIKLAUS U.In this work we study a microchip laser designed to function as an oscillator in a Master-Oscillator Power-Amplifier (MOPA) system targeted for laser tattoo removal. Different configurations of the Nd: YAG resonator were used by changing the output coupler mirror reflectivities and the initial transmission of the Q-switch. The quasi-CW resonator provided 55.4 W of output with 51.31% and 78.2% optical and slope efficiencies, respectively. For Q-switched operation, the best configuration resulted in a peak output power of 3.6 MW with 588 ps pulse width.Artigo IPEN-doc 30183 Compact, high power CW ring laser resonator2023 - BERECZKI, ALLAN; MENEZES, FELIPE C. de; WETTER, NIKLAUS U.We demonstrated the dynamically stable operation of aNd: YAG ring laser with 51.8 W of linearly polarized, continuous output power. The laser was based on laser modules side-pumped by diode bars. The resonator, aimed at single-frequency operation, is a design improvement from a previous work with the resonator length 4.3 times smaller than the previous design, thus resulting in a larger free spectral range, favoring for operation at single-frequency.Artigo IPEN-doc 30048 Micro-Raman spectroscopy identification of hydroxyapatite in dental pulp stem cells2023 - SILVA, FLAVIA R.O.; PASCOAL, DIEGO R.C.; BERECZKI, ALLAN; SIPERT, CARLA R.; BRAGA, ROBERTO R.; BELLINI, MARIA H.; SILVA, LUIS F.T.; FREITAS, ANDERSON Z.; WETTER, NIKLAUS U.Cell differentiation using calcium phosphate nanoparticles was studied. The hydroxyapatite was internalized in human dental pulp stem cells and characterized by Raman spectroscopy. Raman spectra showed the hydroxyapatite distribution in nanoparticles nodules in the cells.Artigo IPEN-doc 30047 Direct nanoplastics detection below the diffraction limit using micro Raman2023 - BERECZKI, ALLAN; DIPOLD, JESSICA; FREITAS, ANDERSON Z.; WETTER, NIKLAUSRaman spectra of polystyrene nanoparticles of 50 nm diameter were directly measured using micro-Raman spectroscopy. Data analysis demonstrated that particles as small as 20 nm could be directly measured with this simple and robust technique.Artigo IPEN-doc 29353 Raman Spectroscopy of irradiated and non-irradiated plastics2022 - DIPOLD, JESSICA; BERECZKI, ALLAN; PINHEIRO, GUSTAVO; VASCONCELOS, KAMILLA; FREITAS, ANDERSON Z. de; WETTER, NIKLAUS U.Understanding radiation damage to plastic is of great interest for possible construction applications. Two different plastics were gamma irradiated and their property changes were studied with micro-Raman spectroscopy, showing promising results in increasing its toughness.Artigo IPEN-doc 29350 Compact, high-power, single-frequency, dynamically stable cw ring laser2022 - BERECZKI, ALLAN; WETTER, NIKLAUSWe recently reported a single-frequency Nd:YAG ring laser with 55.6 W CW output. In this work our design equations are given in order to obtain compactness and increasing resonator free spectral range.Artigo IPEN-doc 28755 Adaptive, high-power, dynamically stable ring resonator2022 - BERECZKI, A.; WETTER, NIKLAUS U.Dynamically stable resonators have a stationary TEM00 beam waist inside the laser rod (w30), which is minimal throughout the stability interval and insensitive to changes in pump power. For a given set of resonator parameters (mirror radii and distances between mirrors and rods), the stability interval parameters, which are the limits of the stability interval in terms of the rod’s thermally induced focusing length are determined. In linear resonators, these stability interval parameters cannot be changed independently only by varying resonator distances, and mirrors of different curvature have to be employed. However, our group showed recently that for a symmetric ring resonator containing a pair of curved mirrors, the width of stability interval and the stability interval limit at maximum rod’s focal length can be adjusted continuously and independently only by varying resonator distances once the mirror radius of curvature has been fixed. In this work we demonstrate a project of an adaptive ring resonator that allows the TEM00 - mode resonator to be continuously tuned throughout the whole range of pump powers utilizing standard electromechanics to move the mirrors. Additionally for a given value of pump power, w30 can be varied, thus allowing different beam qualities to be obtained from the same resonator.Artigo IPEN-doc 27334 Polydispersed Nd3+:YVO4+SiO2 powders for highly efficient random lasers2020 - DIPOLD, JESSICA; SILVA, DANILO A.A. da; BERECZKI, ALLAN; JIMENEZ-VILLAR, E.; WETTER, NIKLAUS U.Random lasers are cheap and easy to fabricate, having several different applications such as early cancer detection, encryption and Speckle-free imaging. However, few fabricated random lasers present high efficiency, which limits their possible applications. In a recent work, our group achieved a record efficiency by developing random lasers that use compacted, polydispersed yttrium vanadate doped with neodymium (Nd3+:YVO4 ) powders to create separate regions for gain and light diffusion. Large particles are responsible for the light diffusion, while the small particles that occupy the spaces between them create gain pockets, absorbing the pumped light. In this work, this strategy is refined by using passive particles (SiO2) for light diffusion, restricting the laser active particles to the gain pockets. The first attempt with this strategy used 30% of Nd3+:YVO4 small powders and 70% of large SiO2 particles. Without any further optimization, the result achieved is already 40% of the highest obtained efficiency in the previously studied Nd3+:YVO4 polydisperse sample, showing a promising result to further improve this new strategy and reach even larger efficiencies with less laser active material.Artigo IPEN-doc 27332 Three-level Nd:YLF Raman laser directly pumped by a beam shaped diode bar2020 - BERECZKI, A.; PAES, JOAO P.F.; WETTER, NIKLAUS U.Low heat generation can be obtained when pumping Nd:YLF at wavelengths of 872 nm and 880 nm and emitting at the three-level transition of 908 nm. These transitions show very low quantum defect with efficiencies of 0.96 and 0.97, respectively. However, the low average absorption cross-section at these wavelengths makes efficient absorption even for longitudinal pump setups difficult. Using a beam-shaped pump diode instead of a fiber-coupled diode bar may be an effective means of increasing absorption because it can provide for π-polarized radiation which shows higher absorption cross section. In this work, a Nd:YLF was pumped at 872 nm by a diode bar using beam-shaping. Results were compared to pumping at 872 and 880 nm with non-polarized fiber-coupled diodes. Stimulated Raman scattering was also obtained with a KGW crystal generating first Stokes emissions at 990 nm and 976 nm.Artigo IPEN-doc 27331 Dynamically stable lasers from commercial Nd:YAG modules with high beam quality and single-frequency2020 - BERECZKI, A.; WETTER, NIKLAUS U.Diode-side pump Nd:YAG rod modules are widely available, reliable and commercially very attractive for building continuous-wave solid-state lasers in the 10-1000 W range. Newer technologies such as fiber or thin disk lasers are generally much more expensive but have the benefit of better beam quality and higher output powers if necessary. By using well-known techniques for designing dynamically stable resonators (DSRs), lasers with high extraction efficiency and high beam quality (fundamental mode, TEM00) can be obtained also with diode side-pumped modules. However, a successful project for a dynamic stable laser depends critically on the correct choice of the fundamental mode diameter within the rod. DSR design rules are based on the beam waist, w3, at the rod principal planes by considering the rod as a thin thermal lens, which differs significantly from real resonators. Here we give guidelines and criteria on how to establish the correct diameter in each case. Using off-the-shelf 75 W Nd:YAG modules it was possible to obtain linearly polarized TEM00-mode output of 30 W with M2=1.08 from a single module, M2=1.2 and 76.5 W of output power using two modules and 100.5 W of polarized, continuous output with M2=1.8. A single-frequency ring laser was also built, using two modules, generating 51.6 W of fundamental wave single-frequency output.