Optical trapping with superfocused high-M2 laser diode beam

Many applications of high-power laser diodes demand tight focusing. This is often not possible due to the multimode nature of semiconductor laser radiation possessing beam propagation parameter M2 values in double-digits. We propose a method of 'interference' superfocusing of high-M2 diode laser beams with a technique developed for the generation of Bessel beams based on the employment of an axicon fabricated on the tip of a 100 μm diameter optical fiber with highprecision direct laser writing. Using axicons with apex angle 140º and rounded tip area as small as 10 μm diameter, we demonstrate 2-4 μm diameter focused laser 'needle' beams with approximately 20 μm propagation length generated from multimode diode laser with beam propagation parameter M2=18 and emission wavelength of 960 nm. This is a few-fold reduction compared to the minimal focal spot size of 11 μm that could be achieved if focused by an 'ideal' lens of unity numerical aperture. The same technique using a 160º axicon allowed us to demonstrate few-μm-wide laser 'needle' beams with nearly 100 μm propagation length with which to demonstrate optical trapping of 5-6 μm rat blood red cells in a water-heparin solution. Our results indicate the good potential of superfocused diode laser beams for applications relating to optical trapping and manipulation of microscopic objects including living biological objects with aspirations towards subsequent novel lab-on-chip configurations.

Superfocusing of high-M2 semiconductor laser beams:experimental demonstration

The focusing of multimode laser diode beams is probably the most significant problem that hinders the expansion of the high-power semiconductor lasers in many spatially-demanding applications. Generally, the 'quality' of laser beams is characterized by so-called 'beam propagation parameter' M2, which is defined as the ratio of the divergence of the laser beam to that of a diffraction-limited counterpart. Therefore, M2 determines the ratio of the beam focal-spot size to that of the 'ideal' Gaussian beam focused by the same optical system. Typically, M2 takes the value of 20-50 for high-power broad-stripe laser diodes thus making the focal-spot 1-2 orders of magnitude larger than the diffraction limit. The idea of 'superfocusing' for high-M2 beams relies on a technique developed for the generation of Bessel beams from laser diodes using a cone-shaped lens (axicon). With traditional focusing of multimode radiation, different curvatures of the wavefronts of the various constituent modes lead to a shift of their focal points along the optical axis that in turn implies larger focal-spot sizes with correspondingly increased values of M2. In contrast, the generation of a Bessel-type beam with an axicon relies on 'self-interference' of each mode thus eliminating the underlying reason for an increase in the focal-spot size. For an experimental demonstration of the proposed technique, we used a fiber-coupled laser diode with M2 below 20 and an emission wavelength in ~1μm range. Utilization of the axicons with apex angle of 140deg, made by direct laser writing on a fiber tip, enabled the demonstration of an order of magnitude decrease of the focal-spot size compared to that achievable using an 'ideal' lens of unity numerical aperture. © 2014 SPIE.

Avaliação in vivo do potencial regenerativo na Degeneração Walleriana de nervos periféricos - com a utilização de laser de baixa potência e composto polivitamínico 3-NERVE

Dissertação (Mestrado em Tecnologia Nuclear)

Determinação de metais em óleos lubrificantes utilizando a técnica de espectrometria de emissão óptica com plasma induzido por laser

IPEN/D

Sensoriamento remoto a laser de aerossóis em uma refinaria de petróleo

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Nenneguya garavelli n. sp and Myxobolus peculiaris n. sp (Myxozoa : Myxobolidae) in the gills of Cyphocharax nagelli (Osteichthyes : Curimatidae) from Rio do Peixe Reservoir, Sao Jose do Rio Pardo, São Paulo, Brazil

The present work describes myxozoans found in Cyphocharax nagelli (Characiformes: Curimatinae) commonly called saguiru collected from Rio do Peixe Reservoir, Sao Jose do Rio Pardo, São Paulo, Brazil. From a total of 38 examined fish, 24 were infected with Henneguya garavelli n. sp. (63% prevalence) and two with Myxobolus peculiaris n. sp. (5% prevalence) in the gills. Spores were studied by staining and fresh spores were observed by differential interference contrast optics. Henneguya garavelli n. sp. differs from Henneguya iheringi , Henneguya occulta, Henneguya cesarpintoi, Henneguya santae, Henneguya pisciforme, Henneguya amazonica, Henneguya striolata, Henneguya leporinicola and Henneguya chydadea in spore length and from Henneguya travassosi, Henneguya adherens, Henneguya malabarica, Henneguya piaractus and also Henneguya chydadea in polar capsule length and tail length. Myxobolus peculiaris n. sp. was very different when compared to other species of Myxobolus in its morphology and the biggest size of spore body. The authors present tables with comparative measurements of Brazilian myxozoan parasites. (c) 2006 Elsevier B.V. All rights reserved.

MULTI-WAVELENGTH SPECKLE REDUCTION FOR LASER PICO-PROJECTORS USING DIFFRACTIVE OPTICS

Personal electronic devices, such as cell phones and tablets, continue to decrease in size while the number of features and add-ons keep increasing. One particular feature of great interest is an integrated projector system. Laser pico-projectors have been considered, but the technology has not been developed enough to warrant integration. With new advancements in diode technology and MEMS devices, laser-based projection is currently being advanced for pico-projectors. A primary problem encountered when using a pico-projector is coherent interference known as speckle. Laser speckle can lead to eye irritation and headaches after prolonged viewing. Diffractive optical elements known as diffusers have been examined as a means to lower speckle contrast. Diffusers are often rotated to achieve temporal averaging of the spatial phase pattern provided by diffuser surface. While diffusers are unable to completely eliminate speckle, they can be utilized to decrease the resultant contrast to provide a more visually acceptable image. This dissertation measures the reduction in speckle contrast achievable through the use of diffractive diffusers. A theoretical Fourier optics model is used to provide the diffuser’s stationary and in-motion performance in terms of the resultant contrast level. Contrast measurements of two diffractive diffusers are calculated theoretically and compared with experimental results. In addition, a novel binary diffuser design based on Hadamard matrices will be presented. Using two static in-line Hadamard diffusers eliminates the need for rotation or vibration of the diffuser for temporal averaging. Two Hadamard diffusers were fabricated and contrast values were subsequently measured, showing good agreement with theory and simulated values. Monochromatic speckle contrast values of 0.40 were achieved using the Hadamard diffusers. Finally, color laser projection devices require the use of red, green, and blue laser sources; therefore, using a monochromatic diffractive diffuser may not optimal for color speckle contrast reduction. A simulation of the Hadamard diffusers is conducted to determine the optimum spacing between the two diffusers for polychromatic speckle reduction. Experimental measured results are presented using the optimal spacing of Hadamard diffusers for RGB color speckle reduction, showing 60% reduction in contrast.

Fitness cost and interference of Arm/Rmt aminoglycoside resistance with the RsmF housekeeping methyltransferases

Arm/Rmt methyltransferases have emerged recently in pathogenic bacteria as enzymes that confer high-level resistance to 4,6-disubstituted aminoglycosides through methylation of the G1405 residue in the 16S rRNA (like ArmA and RmtA to -E). In prokaryotes, nucleotide methylations are the most common type of rRNA modification, and they are introduced posttranscriptionally by a variety of site-specific housekeeping enzymes to optimize ribosomal function. Here we show that while the aminoglycoside resistance methyltransferase RmtC methylates G1405, it impedes methylation of the housekeeping methyltransferase RsmF at position C1407, a nucleotide that, like G1405, forms part of the aminoglycoside binding pocket of the 16S rRNA. To understand the origin and consequences of this phenomenon, we constructed a series of in-frame knockout and knock-in mutants of Escherichia coli, corresponding to the genotypes rsmF(+), ΔrsmF, rsmF(+) rmtC(+), and ΔrsmF rmtC(+). When analyzed for the antimicrobial resistance pattern, the ΔrsmF bacteria had a decreased susceptibility to aminoglycosides, including 4,6- and 4,5-deoxystreptamine aminoglycosides, showing that the housekeeping methylation at C1407 is involved in intrinsic aminoglycoside susceptibility in E. coli. Competition experiments between the isogenic E. coli strains showed that, contrary to expectation, acquisition of rmtC does not entail a fitness cost for the bacterium. Finally, matrix-assisted laser desorption ionization (MALDI) mass spectrometry allowed us to determine that RmtC methylates the G1405 residue not only in presence but also in the absence of aminoglycoside antibiotics. Thus, the coupling between housekeeping and acquired methyltransferases subverts the methylation architecture of the 16S rRNA but elicits Arm/Rmt methyltransferases to be selected and retained, posing an important threat to the usefulness of aminoglycosides worldwide.

IDENTIFICAÇÃO POLIFÁSICA DE GONGRONELLA SP. E DE RHIZOPUS SP. DEGRADADORES DO FUNGICIDA SISTÉMICO METALAXIL

A capacidade destes fungos degradarem compostos xenobióticos e recalcitrantes é uma característica biotecnologicamente importante tornando-os potencialmente úteis para processos de biorremediação. Gongronella sp. e Rhizopus sp. foram isolados do solo de vinhas da região do Alentejo, Portugal. Estes isolados mostraram elevada capacidade de degradarem o fungicida acilalanina metalaxil. No presente estudo, para a identificação polifásica de Gongronella sp. e Rhizopus sp., presuntivamente identificado como R. stolonifer, várias linhagens de referência da ordem Mucorales (Absidia, Circinella, Gongronella e Rhizopus) foram incluídas. A abordagem polifásica combinou a análise das macro- e micromorfologias, a análise da sequência inteira da região ITS ribossomal (i.e., ITS1/5.8S rDNA/ITS2) e ainda o uso da espectrometria de massas por Matrix Assisted Laser Desorption Ionization Time-of-Flight (MALDI-TOF).