Página 1 dos resultados de 72 itens digitais encontrados em 0.010 segundos

Influence of effective number of pulses on the morphological structure of teeth and bovine femur after femtosecond laser ablation

Nicolodelli, Gustavo; Zanirato Lizarelli, Rosane de Fatima; Bagnato, Vanderlei Salvador
Fonte: SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS; BELLINGHAM Publicador: SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS; BELLINGHAM
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.29%
Femtosecond lasers have been widely used in laser surgery as an instrument for contact-free tissue removal of hard dental, restorative materials, and osseous tissues, complementing conventional drilling or cutting tools. In order to obtain a laser system that provides an ablation efficiency comparable to mechanical instruments, the laser pulse rate must be maximal without causing thermal damage. The aim of this study was to compare the different morphological characteristics of the hard tissue after exposure to lasers operating in the femtosecond pulse regime. Two different kinds of samples were irradiated: dentin from human extracted teeth and bovine femur samples. Different procedures were applied, while paying special care to preserving the structures. The incubation factor S was calculated to be 0.788 +/- 0.004 for the bovine femur bone. These results indicate that the incubation effect is still substantial during the femtosecond laser ablation of hard tissues. The plasma-induced ablation has reduced side effects, i.e., we observe less thermal and mechanical damage when using a superficial femtosecond laser irradiation close to the threshold conditions. In the femtosecond regime, the morphology characteristics of the cavity were strongly influenced by the change of the effective number of pulses. (C) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.JBO.17.4.048001]; Fundacao de Amparo a Pesquisa do Estado de Rio Paulo (Fapesp); Fundacao de Amparo a Pesquisa do Estado de Rio Paulo (Fapesp); National Counsel of Technological and Scientific Development (CNPq); National Counsel of Technological and Scientific Development (CNPq)

Avaliação de um vitrocerâmico elaborado a partir do genérico do biovidro 45S5 em perfurações de tíbias de ratos, e seu comportamento sob influência da radiação laser de baixa intensidade; Evaluation of a glass ceramic produced from the generic of bioglass 45S5 in drilling of tibias of rats, and their behavior under the influence of low-intensity laser radiation

Arruda, Emiliano Rodrigo de Barros
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 26/08/2008 PT
Relevância na Pesquisa
36.33%
O presente trabalho avaliou os efeitos provocados pela laserterapia de baixa intensidade (LTBI) no 'lâmbda' 780 nm, 30 mW de potência e tempo de exposição de 150 segundos, resultando em uma fluência de 112,5 J/'CM POT.2' e energia total de 4,5 J, sobre o comportamento osteocondutor da vitrocerâmica elaborada a partir do genérico do biovidro de composição: 45% 'SI'O IND.2', 24,5% 'NA IND.2'O', 24,5% 'CA'O' e 6% 'P IND.2'O IND.5' em perfurações ósseas em tíbias de ratos. O biovidro foi recozido em cuba de inox acima de sua temperatura de transição vítrea, a 620 graus Celsius por 30 minutos e mantido a 790 graus Celsius por 60 minutos, em seguida foi realizada a espectroscopia Raman para verificar a cristalinidade. Foram realizadas perfurações abaixo da tuberosidade da tíbia direita de 64 machos de ratos da raça Wistar (Rattus norvegicus albinus) na idade adulta. Os mesmos foram divididos aleatoriamente em 4 grupos sendo eles: um controle e três submetidos à procedimento experimental de implante e/ou irradiação laser de baixa intensidade. Em todos os grupos foram utilizados 16 indivíduos. Posteriormente, os animais de cada grupo foram subdivididos em dois subgrupos cada, de acordo com o tempo de vida antes da eutanásia...

Desenvolvimento de um sistema óptico para microperfuração de materiais cerâmicos,metálicos e poliméricos utilizando laser nanopulsado de Nd:YAG; Not available

Fossa, João Sergio
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 15/05/2007 PT
Relevância na Pesquisa
36.57%
Neste trabalho foi desenvolvido e caracterizado um aparato óptico para geração de padrões de perfurações em escala micrométrica em diversas classes de materiais. Este sistema, fundamentado nas técnicas de percussão e trepanação, foi acoplado a um laser industrial nanopulsado de Nd:YAG operando em 532 nm. Sua viabilidade foi analisada em amostras de alumínio metálico, cerâmica de α−alumina, poli(cloreto de vinila) (PVC) e silício cristalino. Verificou-se que as melhores condições para a obtenção de microperfurações de precisão são proporcionadas pelo método de trepanação assistido por um alto fluxo de ar. Micrografias eletrônicas comprovaram que estes parâmetros resultam em microperfurações simétricas, precisas e, geralmente, desprovidas de rebarbas. Suas dimensões, comparadas ao método de percussão, são evidentemente superiores devido à maior quantidade de material processado nesta técnica. Verificou-se que os diâmetros de microperfurações por percussão variaram de 25 a 200 µm enquanto que pelo método de trepanação estes resultados foram de aproximadamente 50 a 240 µm, dependendo das propriedades do material e da fluência aplicada. Um estudo sobre a velocidade de perfuração em função da fluência incidente comprovou a alta dependência da taxa de ablação com relação às propriedades térmicas e ópticas dos materiais. A análise de secções retas transversais em microperfurações obtidas por percussão e trepanação também indicou a formação de deformações internas em materiais com baixas velocidades de perfuração...

Studies of new occurrences of bentonite clays in the State of Paraíba for use in water based drilling fluids

Silva,Isabelle A.; Costa,Julliana Marques R.; Menezes,Romualdo R.; Ferreira,Heber S.; Neves,Gelmires de A.; Ferreira,Heber C.
Fonte: Escola de Minas Publicador: Escola de Minas
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2013 EN
Relevância na Pesquisa
36.38%
New bentonite clay deposits have recently been discovered in the state of Paraíba, mainly in the municipalities of Cubati and Pedra Lavrada, creating great expectations in view of the possibility of expanding industrial production using these new reserves. The aim of this study was to study the new occurrences of bentonite clay in Paraíba, particularly in the municipality of Pedra Lavrada, for use in water based drilling fluids. The mineralogical properties of the clays were characterized by particle size analysis using laser diffraction, and thermogravimetric and differential thermal analysis, and its chemical composition was analyzed by X-ray fluorescence, X-ray diffraction, cation exchange capacity and specific surface area. The bentonite clays were treated with sodium carbonate at concentrations of 75, 100, 125, 150 and 175mEq/100g of dry clay, to transform them from polycationic to sodium form. For the technological characterization, drilling fluids were prepared according to the standards of Petrobras. The results indicated that the mineralogical composition of the samples consisted of montmorillonite, kaolinite and quartz. As for their rheological properties, the samples were found to partially meet the rheological requirements of the Petrobras standard.

Análise histológica comparativa do reparo ósseo em osteotomias realizadas por laser de Er:Yag e broca cirúrgica, submetidas à laserterapia de baixa potência

Mello, Elaine Duarte Artuso de
Fonte: Pontifícia Universidade Católica do Rio Grande do Sul; Porto Alegre Publicador: Pontifícia Universidade Católica do Rio Grande do Sul; Porto Alegre
Tipo: Tese de Doutorado
PORTUGUêS
Relevância na Pesquisa
36.6%
O propósito deste estudo foi comparar o processo de reparo ósseo após osteotomias realizadas em tíbias de ratos por laser de Er:YAG (comprimento de onda de 2,94 μm) e broca cirúrgica em baixa rotação, sob irrigação, submetidas à terapia de laser de baixa potência (LLLT), com laser de diodo (InGaAlP e GaAIAs), nos comprimentos de onda de 695 nm e 830 nm. Foram utilizados 54 ratos Wistar adultos. Os animais foram divididos em seis grupos: Grupo 1, osteotomia com laser Er:YAG; Grupo 2, osteotomia com laser Er:YAG e LLLT de 685 nm; Grupo 3, osteotomia com laser Er:YAG e LLLT de 830 nm; Grupo 4, osteotomia com broca em baixa rotação; Grupo 5, osteotomia com broca em baixa rotação e LLLT de 685 nm; Grupo 6, osteotomia com broca em baixa rotação e LLLT de 830 nm. O laser de Er:YAG foi utilizado no modo super-pulsado (Q-switch), sem contato, 10 Hz, 500 mJ. Três animais de cada grupo foram mortos aos 7, 14 e 21 dias da cirurgia. Os espécimes obtidos foram corados em HE e analisados sob microscopia óptica. Aos 7 e 14 dias da cirurgia, os grupos do laser de Er:YAG apresentaram a melhor condição de reparo tecidual, comparativamente aos grupos que realizaram osteotomias com broca cirúrgica. O laser de Er:YAG promoveu com sucesso a ablação do tecido ósseo...

Incorporação de resíduo de perfuração em matriz cerâmica: estabilização por solidificação; Residue incorporation drilling ceramic matrix: stabilization by solidilication

Câmara, Ana Paula Costa
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Química; Pesquisa e Desenvolvimento de Tecnologias Regionais Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Química; Pesquisa e Desenvolvimento de Tecnologias Regionais
Tipo: Tese de Doutorado Formato: application/pdf
POR
Relevância na Pesquisa
36.57%
One of the waste generated during the drilling of oil wells are gravel which are impregnated of drilling fluid. This residue consists of highly toxic chemicals, including toxic metals. This study suggests an alternative process to the treatment of this waste, by incorporating it the form of raw material in the ceramic matrix , and by solidification and stabilize the metals present, Aluminum (Al), Iron (Fe), Manganese (Mn) and Zinc (Zn). The raw materials were characterized by the techniques of X ray fluorescence (FRX), X ray diffraction (DRX), laser granulometry (GL), thermogravimetry (TG) and differential thermal analysis (ADT). To evaluate the percentage of gravel effect the environmental and technological properties were obtained from formulations containing 0, 10 and 20 % by weight of gravel in the ceramic matrix. After sintering at temperatures 1080, 1120 and 1160 °C, the samples were tested for water absorption, the linear shrinkage firing, voltage of rupture and solubility. The results obtained showed that the stabilization by solidification, is a viable alternative to safe disposal of waste drilling. Ceramics products can be used in the manufacture of solid bricks; Conselho Nacional de Desenvolvimento Científico e Tecnológico; Um dos resíduos gerados durante a perfuração de poços de petróleo são os cascalhos que ficam impregnados por fluido de perfuração. Este resíduo é composto por produtos químicos de alta toxidade...

Avaliação do efeito osteogênico do laser de baixa potencia (808nm e 660nm) sobre defeitos ósseos produzidos no fêmur de ratas submetidas à ovariectomia

Poppi, Rodrigo Ré
Fonte: Universidade Federal de Mato Grosso do Sul Publicador: Universidade Federal de Mato Grosso do Sul
Tipo: Dissertação de Mestrado
POR
Relevância na Pesquisa
36.25%
O presente estudo teve como objetivo avaliar o efeito do laser de baixa potência com comprimento de onda de 660nm e 808nm sobre o processo de reparação de defeitos ósseos produzidos no fêmur de ratas submetidas à ovariectomia. Para tanto foi realizada ovariectomia bilateral em 18 ratas de linhagem Wistar distribuídas em grupo controle e irradiado após a comprovação da diminuição da massa óssea através de análise digital da densidade óssea, foi realizado uma perfuração padronizada no fêmur. Os grupos irradiados receberam 120J/cm2 dos lasers As-Ga-Al (660nm) e In-Ga-Al-P (808nm). Os animais foram submetidos à eutanásia em 14 e 21 dias após confecção do defeito ósseo. A avaliação histológica dos eventos ocorridos foi feita de forma descritiva, utilizando-se de um método semi-quantitativo através de microscopia óptica. Os resultados nos períodos de 14 e 21 dias mostraram que os grupos irradiados apresentaram superfície osteoblástica, fibroblástica e de osteócitos imaturos, significativamente maiores que o grupo controle (p<0,05). Análise de reação inflamatória mostrou que a TLB foi eficaz, pois, poucas células inflamatórias foram encontradas quando comparadas ao grupo controle com p<0,05. Conclui-se no modelo experimental estudado que ambos os comprimentos de ondas utilizados induziram a proliferação de células responsáveis pela consolidação óssea.; The present study aimed to evaluate the effect of low level laser with 660nm e 808nm wavelength on the process of reparation of bone defects produced on the femur of female rats submitted to ovarectomy. For such...

Distribution of leukocyte subtypes in the sheep ovary after laser drilling

Tozawa, H.; Brannstrom, M.; Petrucco, O.; Walker, S.; Chambers, H.; Pascoe, V.; Norman, R.
Fonte: IRL Press Publicador: IRL Press
Tipo: Artigo de Revista Científica
Publicado em //1995 EN
Relevância na Pesquisa
66.83%
The distribution of leukocyte subtypes in the sheep ovary following laser drilling of the ovarian capsule was examined to understand a possible mechanism by which this treatment promotes ovulation in polycystic ovarian syndrome. Ovaries were removed from sheep at different time-points following laparoscopic laser drilling and immunohistochemical detection of leukocyte subtypes, using specific monoclonal antibodies; standard histological staining was performed. Migration of leukocytes into the laser-drilled site was observed as early as 6 h after laser drilling and the total number of leukocytes in the site was found to increase up to the 12th day after surgery. In the earlier period, polymorphonuclear leukocytes were the dominant leukocyte subtypes, while macrophages and lymphocytes were the major cellular components on the 12th day and later. These results show that the tissue changes in the ovary following laser drilling are consistent with a local inflammatory reaction. The prolonged appearance of numerous macrophages following the acute inflammatory phase could lead to the secretion of cytokines and other substances suggested to be important in promoting ovulation. These data indicate that part of the effectiveness of the laser drilling in polycystic ovarian syndrome may be attributable to the secretory products of these leukocytes.; H.Tozawa...

Inline Coherent Imaging

WEBSTER, PAUL J L
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
26.64%
In laser materials processing, the direct measurement and characterization of material and process depth is traditionally a diffcult task. This is particularly difficult when such information needs to be obtained in real-time for feedback and dynamic analysis applications. This thesis outlines a novel method and apparatus for real-time depth measurement during laser processes such as welding, drilling, cutting and ablation called inline coherent imaging (ICI). The approach borrows the coherent imaging ideas from the primarily medical field of optical coherence tomography and adapts them to the new application. Without requirements for flawless image quality and limitations on sample exposure the design is free to emphasize speed in acquisition and processing. Furthermore, the imaging optics are specialized for compatibility with off-the-shelf beam delivery systems. Several generations of the imaging technique and relevant design equations are described and shown and realized. Also described is the design and construction of two laser processing stations used for testing ICI in macro- and micro-processing applications. A variety of applications for ICI in the understanding of percussion drilling and welding of metals and other industrial materials are discussed. The imaging technique is further extended to provide manual and fully automatic closed-loop control of drilling and ablation processes in industrial materials. Finally...

Inline Coherent Imaging Based Control of Laser Machining Processes using a Field-Programmable Gate Array

Jenkins, Ethan
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
36.22%
Lasers are becoming an increasingly popular tool for use in industrial manufacturing settings. Their high power density, contact-free nature, and ease of automation give them an edge over traditional methods in processes such as welding, cutting, and drilling. However, laser beams are a difficult tool to control since they are made of light. Therefore, they cannot be monitored in the same way as a mechanical tool with constant physical dimensions. A recent invention, inline coherent imaging (ICI), uses the interference properties of light to monitor the depth of the processing beam at high speeds. However, the computational demands of ICI data processing are intensive, and it is difficult for standard computers to keep up with the high volumes of data that are output by an ICI system. As a result, the real-time control capabilities of ICI are limited by the rate at which the computer can process the data. In this work, I present a system that uses a field-programmable gate array (FPGA) to process ICI data with a high level of determinism and low latency compared to computer-based ICI. The algorithms that were developed to take advantage of the FPGA's architecture are presented, followed by a detailed description of how they were implemented programmatically. I also describe the hardware that was used to perform experiments with closed-loop ICI feedback control. Finally...

Controlled fiber laser bone ablation using inline coherent imaging

Yin, CHENMAN
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
36.33%
Laser material processing is becoming increasingly popular in various disciplines of science and industry due to its clean and quiet operation, absence of tool wear and high positioning accuracy. In particular, laser osteotomy ("bone cutting") offers new opportunities with its well-identified advantages over conventional methods utilizing mechanical saws/drills. However, lack of depth control is a long-standing barrier to wide clinical implementation. In-process monitoring and real-time feedback is highly desirable for depth-sensitive surgical operations where cutting is performed above critical tissues (e.g., brain surgery). In this work, a low-coherence imaging technique known as inline coherent imaging (ICI) is utilized to monitor bone ablation processes and provide depth information about the sample with on-the-fly signal processing. ICI is analogous to spectral domain optical coherence tomography with its sample arm built "inline" with the ablation laser beam path. ICI is capable of an imaging speed up to 240 kHz and a high dynamic range of over 60 dB. The laser system used for bone ablation is a 1070 nm ytterbium-doped fiber laser. Its fiber delivery allows flexible cutting angles to access hard-to-reach areas in surgery. Laser bone ablation by the fiber laser is characterized by percussion drilling experiments and ICI depth tracking of the sample. The ablation parameters are optimized for high ablation efficiency and minimal thermal damage. Closed-loop feedback based on in situ ICI measurement is developed to achieve controlled ablation with complexity and high precision. Designed features...

Procédé de perçage par laser : Comparaison entre des données expérimentales et une simulation 2D basée sur la méthode CNEM

GIRARDOT, Jeremy; RANC, Nicolas; SCHNEIDER, Mathieu; LORONG, Philippe; ILLOUL, Lounes; BERTHE, Laurent; FAVIER, Véronique
Fonte: Congrès français de mécanique (21 ; 2013 ; Bordeaux (Gironde) Publicador: Congrès français de mécanique (21 ; 2013 ; Bordeaux (Gironde)
Relevância na Pesquisa
46.48%
This work presents a numerical alternative for the laser drilling simulation problem. Using finite element method is difficult to simulate the hole propagation over time, especially because of moving boundaries due to a fast phase change and high thermal gradients. First, the physical process of the laser drilling and the modeling equations are clarified. Then a comparison between experimental data and simulation outputs regarding the laser peak power is investigated.

Investigation of delamination mechanisms during a laser drilling on a cobalt-base superalloy

GIRARDOT, Jeremy; SCHNEIDER, Matthieu; BERTHE, Laurent; FAVIER, Véronique
Fonte: Elsevier Publicador: Elsevier
EN
Relevância na Pesquisa
66.76%
Temperatures in the high pressure chamber of aircraft engines are continuously increasing to improve the engine efficiency. As a result, constitutive materials such as cobalt and nickel-base superalloys need to be thermally protected. The first protection is a ceramic thermal barrier coating (TBC) cast on all the hot gas-exposed structure. The second protection is provided by a cool air layer realized by the use of a thousand of drills on the parts where a cool air is flowing through. The laser drilling process is used to realize these holes at acute angles. It has been shown on coated single crystal nickel-base superalloy that the laser drilling process causes an interfacial cracking (also called delamination), detected by a cross section observation. The present work aims at characterizing interfacial cracking induced by laser drilling on coated cobalt-base super alloy. On the one hand, this work attempted to quantify the crack by several microscopic observations with regards to the most significant process parameters related as the angle beam. On the other hand, we studied the difference of the laser/ceramic and the laser/substrate interaction with real time observation by using a fast movie camera.

Gas investigation for laser drilling

SCHNEIDER, Matthieu; BERTHE, Laurent; FABBRO, Rémy; MULLER, Maryse; NIVARD, Mariette
Fonte: AIP Publicador: AIP
EN
Relevância na Pesquisa
66.52%
Version éditeur : http://jla.aip.org/resource/1/jlapen/v19/i3/p165_s1?isAuthorized=no; This article deals with the gas effect on percussion laser drilling in ms pulse duration range. On the one hand, the flow of assistance gas jet is investigated with and without a target using a strioscopy setup and Pitot’s tube. By this way, the position of shock waves in the supersonic jet and near the target surface is revealed. From this characterization, the distance between exit nozzle and target can be optimized to induce higher pressure on surface and protect optics from liquid ejection. On the other hand, metal liquid and vapor jets from irradiated target are observed with a high-speed camera (100 000 Img/sec). Without assistance gas, a surprising result on the video is a shock wave inside the metal vapor jet like a supersonic flow. The assistance gas limits the propagation of the vapor and facilitates the deposition of metallic liquid around the front surface holes.

Measurement of laser absorptivity for operating parameters characteristic of laser drilling regime

SCHNEIDER, Matthieu; BERTHE, Laurent; FABBRO, Rémy; MULLER, Maryse
Fonte: IOP Publicador: IOP
EN
Relevância na Pesquisa
66.78%
Publisher version : http://iopscience.iop.org/0022-3727/41/15/155502/; Laser drilling in the percussion regime is commonly used in the aircraft industry to drill sub-millimetre holes in metallic targets. Characteristic laser intensities in the range of 10 MW cm−2 are typically employed for drilling metallic targets. With these intensities the temperature of the irradiated matter is above the vaporization temperature and the drilling process is led by hydrodynamic effects. Although the main physical processes involved are identified, this process is not correctly understood or completely controlled. A major characteristic coefficient of laser–matter interaction for this regime, which is the absorptivity of the laser on the irradiated surface, is still unknown, because of the perturbing effects due to laser beam geometrical trapping inside the drilled hole. So, by using time resolved experiments, this study deals with the direct measurement of the variation of the intrinsic absorption of aluminium, nickel and steel materials, as a function of the incident laser intensity up to 20 MW cm−2. We observe that for this incident intensity, the absorptivity can reach up to 80%. This very high and unexpected value is discussed by considering the microscopic behaviour of the heated matter near the vapour–liquid interface that undergoes possible Rayleigh–Taylor instability or volume absorption

A fast method for morphological analysis of laser drilling holes

SCHNEIDER, Matthieu; BERTHE, Laurent; MULLER, Maryse; FABBRO, Rémy
Fonte: AIP Publicador: AIP
EN
Relevância na Pesquisa
66.64%
Version éditeur : http://jla.aip.org/resource/1/jlapen/v22/i4/p127_s1?isAuthorized=no; This paper presents an original method for analyzing laser drilled holes. The so-called Direct Observation of Drilled hOle (DODO) method is introduced and its applications. The hole characterization that’s been made is compared with x-ray radiography and cross-section analysis. Direct Observation of Drilled hole provides instantaneously surface state, geometric shape, as well as recast layer structure, without additional operation. Since no mounting resin is used to embed the sample, the preparation for analysis is simplified and, gives access to a 3D analysis of hole morphology. The principle of this technique consists in positioning the drilling axis on the joint plane of a butt configuration. Surfaces of the two parts of the sample to be joined are polished beforehand, to increase the contact surface, and then holes are drilled in the joint plane. Once the sample is drilled, the two parts are split so that one half of the hole is in each part of the sample. The preparation time of DODO method samples is shorter than the polishing time of the classical method. Moreover the implementation of the DODO method is much easier, for quality control as well as process development in laser drilling.; This work has been supported by Commissariat à l’Energie Atomique

Recent Experimental and Theoretical Advances in Microdrilling of Polymers with Ultraviolet Laser Beams

Lazare, Sylvain; Tokarev, Vladimir
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/12/2004
Relevância na Pesquisa
36.6%
Laser drilling becomes of increasing importance when hole diameter is in the range of 10 to 50 mum, for which conventional alternative approaches are becoming difficult and cost inefficient. Furthermore, it is viewed as the technique of choice for a number of composite materials and hard materials which are not readily processed at the microscopic level by contact mechanical tools. We have demonstrated that suitable experimental conditions are capable of producing microholes with record aspect-ratio (up to 600) in pure polymers like PET, PI, PC, PS, PMMA, PEEK,... For example holes of diameter typically 30 mum can be as long as 18 mm, depth at which the drilling rate is getting nearly zero and the profile stationary. Other materials (metals, ceramics) which can be similarly laser microdrilled do not exhibit such very high aspect-ratio. The mechanisms of the drilling process have been studied in details and an original analytical model has been constructed recently. The various experimental results, obtained with the KrF laser, will be reviewed with emphasis on the parameters leading to formation of good holes with high aspect-ratio. For the application it is also important to note that such high values of aspect-ratio are obtained with regular configuration of the KrF laser giving a standard divergence of 3 mrad. However as shown by the model there is still room for improvement by using a beam with a lower divergence (theoretical limit is 0.2 mrad). Further experimental work is now in progress.; Comment: conference invitee internationale

Laser micro-processing of silicon using nanosecond pulse shaped fibre laser at 1 ?m wavelength

Li, Kun
Fonte: University of Cambridge; Department of Engineering; Institute for Manufacturing Publicador: University of Cambridge; Department of Engineering; Institute for Manufacturing
Tipo: Thesis; doctoral; PhD
EN
Relevância na Pesquisa
36.83%
Processing of Si in the semiconductor and solar cell industry has been dominated by the Diode Pumped Solid State (DPSS) Ultraviolet (UV) laser. Recent advances in laser source technology have produced fibre lasers with Master Oscillator Power Amplifier (MOPA) architectures that offer high repetition rates, high operational efficiencies, and pulse modulation controls exceeding those of typical Q-switched DPSS lasers. The aim of this research is to investigate 1 ?m fibre laser machining of Si with a view to identifying the influential laser parameters for optimum processing of high quality, high efficiency micro drilling and surface texturing applications. A secondary aim is to develop a greater understanding of the laser material interactions and material removal mechanism when using fast rise-time nanosecond laser pulse envelopes. The IR fibre laser was able to perform percussion drilling and single pulse machining on the polished Si over a range of intensities up to 1.22 GW/cm2. With the optimum parameters, the micro-sized holes generated by the IR laser have a well defined edge, no heavy recast and no cracks. With a pulse shape of fast rise time (<7.5 ns for a 10-90% rise in signal), a high front peak power zone (approaching 14 kW) and an energetic long tail (40-180 ns)...

In-plane and Out-of-plane Band-gap Properties of a Two-dimensional Triangular Polymer-based Void Channel Photonic Crystal

Zhou, Guangyong; Ventura, Michael James; Straub, Martin; Gu, Min; Ono, Atsushi; Kawata, Satoshi; Wang, Xue-Hua; Kivshar, Yuri
Fonte: American Institute of Physics (AIP) Publicador: American Institute of Physics (AIP)
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.18%
Two-dimensional (2D) triangular photonic crystals were fabricated in a solid polymer material by femtosecond laser drilling of void channels. Transverse electric (TE) mode band gaps were found to be wider and located at shorter wavelengths in comparison with transverse magnetic (TM) mode gaps. The polarization- and angle-dependent transmittance spectra provided a way to estimate the void channel cross section and the effective refractive index. The results demonstrate that the two-dimensional (2D) void channel polymer photonic crystals can be potential polarization-sensitive elements in a photonic chip.

Laser ablation U-series analysis of fossil bones and teeth

Grun, Rainer; Eggins, Stephen; Kinsley, Leslie; Moseley, Hannah-Kate; Sambridge, Malcolm
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.28%
Over the past decade, we have applied laser ablation ICP mass spectrometry U-series analysis to a large number of bones and teeth. The method is fast and provides high-resolution data of U-series isotopes, which give insights into the complexity of uranium migration into, within and out of bones. In this paper, we present our laser ablation approach in detail, from the experimental set up, to data reduction and uranium diffusion modelling. Laser ablation analysis can now be applied with minimum damage. Complete diffusion data sets can be obtained by laser drilling which leaves a hole of around 200. μm in diameter and 1-2. mm depth. If the natural U-diffusion follows a simple single-stage process, valuable age information can be obtained. In other cases, highly complex U-migrations have been observed, which make any age assessment impossible. Two examples from Wadjak and Callao illustrate the potential of nearly non-destructive laser ablation U-series analysis of human skeletal tissues. The results demonstrate the physical presence of modern humans in south-east Asia at a time when our species just started to migrate into Europe.