To see the other types of publications on this topic, follow the link: Lader.
Dissertations / Theses on the topic 'Lader'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Lader.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
OLIVEIRA, MYRIAN COE DE. "A STUDY OF THE SENSITIVITY OF THE LATTICE-LADER STRUCTURE USING STATE VARIABLES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1991. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=9394@1.
Full textAbstract:
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICONa construção de filtros digitais os coeficientes da sua função de transferência, calculados teoricamente, nem sempre podem ser implementados com exatidão. Isto gera o erro de quantização. A análise de sensibilidade permite conhecer tal alteração das especificações teóricas como também avaliar o desempenho do filtro. Este trabalho examina a estrutura Lattice-Ladder, tipo de filtro digital, descrita por equações de estado genéricas. O objetivo é estabelecer expressões de sensibilidade nos domínios do tempo e da freqüência, para resposta impulsional e resposta a uma excitação qualquer.
In the construction of digital filters the coeficientes of its transfer function, calculated theorically, can´t often be implemented with accuracy. This leads to the quantization error. The sensitivy analysis allows to know this deviation from theoretical specifications and allows to estimate filter´s performance. This work examines Lattice- Ladder structure, a type of digital filter, described by generic state equations. The purpose is to establish sensivity expressions in time and frequency domains, for impulse and generic responses.
2
Hilaire, Pierre. "Improved laser vibration ladar." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1998. http://handle.dtic.mil/100.2/ADA359857.
Full textAbstract:
Thesis (M.S. in Applied Physics) Naval Postgraduate School, December 1998."December 1998." Thesis advisor(s): Robert C. Harney, Donald L. Walters. Includes bibliographical references (p. 43). Also available online.
3
Dulgergil, Ebru. "Development Of A Pulsed Fiber Laser For Ladar System." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614635/index.pdf.
Full textAbstract:
In recent years laser technology has increasingly developed with the use of
fiber lasers and this has provided the possibility to implement different techniques in
the defense industry. LADAR is at the forefront of these techniques. Fiber lasers
constitute a perfect source for LADAR systems due to their excellent robustness,
compact size and high-power generation capability. In this study we will explore the
development of a pulsed fiber laser source for a LADAR system that can obtain high
resolution 3D images in eye-safe region.
A high power, all fiber integrated erbium system with strictly single mode
operation in eye-safe region based on MOPA (master oscillator power amplifier)
configuration with seed source and amplifier part was developed. Both the use of an
actively mode locked laser with erbium doped fiber and fiber coupled modulated
distributed feedback diode laser were investigated as seed sources for the amplifier
part. Both erbium doped single clad fiber and erbium-ytterbium doped double clad
gain fiber were used in this amplifier system. After amplification of the actively
mode locked laser, 12 W of average optical power was obtained through single
mode fiber with 1ns pulse duration at 10 MHz which corresponds to 1.2 kW peak
power. For the fiber coupled DFB diode laser, 9.5W average power was obtained
with around 8 ns duration pulses at 100 kHz and about 9.2 W average power was
also obtained with around 700 ps duration pulses at 1 MHz through strictly single
mode fiber at the output of the same amplifier system as was used in the actively
mode locked seed source. In both cases calculated peak power was around 10 kW
v
which is estimated as the highest peak power for an all fiber integrated system with
single mode operation.
The development of such a fiber system with high power capability, compact
size and free of misalignment is expected to be useful for LADAR application as
well as other areas such as eye surgery, 3D silicon processing or any other material
processing applications.
4
Dunmeyer, David Richard 1978. "Laser speckle modeling for three-dimensional metrology and LADAR." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/16763.
Full textAbstract:
Thesis (M.Eng. and S.B.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.Includes bibliographical references (leaves 103-111).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
In this thesis, I developed three-dimensional laser-speckle models to help in the development process of three-dimensional optical-metrology imaging systems. These models were developed to aid in the proof of concept for various three-dimensional metrology techniques. These models were then compared to real-world imaging systems, developed by both the author and other staff at the MIT Lincoln Laboratory, to determine their ability to accurately model said imaging systems. I also looked at the laser speckle statistics associated with mid-field systems in an exo-atmospheric environment as they relate to LADAR.
by David Richard Dunmeyer.
M.Eng.and S.B.
5
Lécz, Zsolt. "Laser ion acceleration from a double-layer metal foil." Phd thesis, TU Darmstadt, 2013. https://tuprints.ulb.tu-darmstadt.de/3335/1/PHD_final.pdf.
Full textAbstract:
The laser-ion acceleration with ultra-intense and ultra-short laser pulses has opened a
new field of accelerator physics over the last decade. Fast development in laser systems are
capable of delivering short pulses of a duration of a few hundred femtoseconds at intensities
between 10^18-10^20 W/cm2. At these high intensities the laser-matter interaction induces
strong charge separation, which leads to electric fields exceeding the acceleration gradients
of conventional devices by 6 orders of magnitude. The particle dynamics and energy
absorption of the laser pulse can be understood by means of high-performance simulation
tools.
In the framework of the LIGHT (Laser Ion Generation, Handling and Transport) project
our goal is to provide an analytical description of the 3D distribution of the protons accelerated
via TNSA (Target Normal Sheath Acceleration). In this acceleration mechanism
the short pulse impinging on a metal foil heats the electrons to relativistic energies, which
triggers the strong charge separation field on the opposite target surface (Debye-sheath).
The accelerated light ions (proton, carbon, oxygen) observed in the experiments originate
from the contamination layer deposited on the surface. The thickness of this layer in the
experiments is not known exactly. According to our study these ions can be accelerated in
three different regimes depending on layer thickness: quasi-static acceleration (QSA, for
thin layers), plasma expansion (for thick layers) and a not well understood intermediate
(or combined) regime.
In a laser-plasma simulations time-dependent hot electron density and temperature are
observed, therefore we performed plasma simulations with a well defined and constant
initial hot electron distribution. Thus the simulation results are easier to compare with
analytical models. In our case the theoretical investigation of the TNSA involves the
understanding of the charge separation effects at the surface of a two-temperature plasma
and the consequent proton acceleration in one dimension. We omit the detailed dynamics
of the laser-plasma interaction by assuming a preheated electron distribution. With our 1D
electrostatic simulations we investigate the influence of the proton layer thickness on the
TNSA energy spectrum. Additionally we investigate the divergence of the protons using
2D simulations: In these we simulate the heating of the electrons by the laser pulse.
Numerical studies in this work were carried out using a Particle-in-Cell (PIC) plasma
simulation code (VORPAL). The target is defined as a single-ionized plasma with a doublelayer
structure: a bulk layer of heavy ions, which represents the metal foil itself and a much
thinner proton layer, which serves as the contamination layer. The layer is considered thin
if it is thinner compared to the skin depth of the accelerating electric field. For a thin
proton layer the quasi-static acceleration is the governing mechanism. When the proton
layer is larger than skin depth the process can be described as plasma expansion.
I found that the energy and phase-space distribution of the protons strongly depends
on the layer thickness. In the QSA regime the proton spectrum shows a nearly monoenergetic
feature, but the maximum energy is typically low compared to the plasma expansion regime, where the protons have a broad exponential energy spectrum. For the
plasma expansion we observe a cut-off energy that logarithmically depends on the acceleration
time.
The simulation results in these two extreme cases for one- and two-temperature plasmas
have been extensively compared to analytical predictions showing an overall good
agreement. In the intermediate regime an analytical expression could be obtained for the
energy conversion from electrons to protons as a function of electron parameters and layer
thickness. By changing the layer thickness a smooth transition between the two extreme
cases could be identified.
The proton layer thickness also has an impact on the transversal acceleration, which
defines the divergence of a proton beam. In the two-dimensional TNSA simulations a laser
pulse is needed to generate the hot electron population in the plasma. The simulations show
that theoretically with the right laser pulse duration and layer thickness the divergence
of the most energetic protons can be reduced almost to zero. In the QSA regime the
transversal distribution and temperature of the hot electrons changes too quickly compared
to the time-scale of the acceleration. The analytical treatment of the divergence is only
possible for the thick layers, where the plasma expansion model is suitable to describe the
physics. The model derived in this work can be used to reconstruct the whole velocity
phase-space of the protons in 3D. Therefore it enables us to perform particle tracking and
beam optics simulations with realistic TSNA proton bunch. The envelope angle of the
protons measured in experiments can be also reproduced using our 2D model.
The beam quality during motion through magnetic focusing and energy selection systems
downstream of the laser acceleration is sensitive to the initial distribution. After
benchmarking our analytic models, simulation results and measurements with each another,
we are confident we can now provide sufficiently realistic particle distributions to be
expected a few mm from the target in TNSA. Using our particle distributions as input, the
effect of co-moving electrons, the degradation of the transverse emittance and chromatic
aberration effects can be investigated. Thereby this study hopefully contributes to the goal
of the Light project: Coupling the new laser ion acceleration techniques to conventional
accelerator facilities.
6
Lutey, Adrian Hugh Alexander <1986>. "High-Speed Laser Processing of Thin Single and Multi-Layer Films." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5741/.
Full textAbstract:
Theoretical models are developed for the continuous-wave and pulsed laser incision and cut of thin single and multi-layer films. A one-dimensional steady-state model establishes the theoretical foundations of the problem by combining a power-balance integral with heat flow in the direction of laser motion. In this approach, classical modelling methods for laser processing are extended by introducing multi-layer optical absorption and thermal properties. The calculation domain is consequently divided in correspondence with the progressive removal of individual layers. A second, time-domain numerical model for the short-pulse laser ablation of metals accounts for changes in optical and thermal properties during a single laser pulse. With sufficient fluence, the target surface is heated towards its critical temperature and homogeneous boiling or "phase explosion" takes place. Improvements are seen over previous works with the more accurate calculation of optical absorption and shielding of the incident beam by the ablation products. A third, general time-domain numerical laser processing model combines ablation depth and energy absorption data from the short-pulse model with two-dimensional heat flow in an arbitrary multi-layer structure. Layer removal is the result of both progressive short-pulse ablation and classical vaporisation due to long-term heating of the sample. At low velocity, pulsed laser exposure of multi-layer films comprising aluminium-plastic and aluminium-paper are found to be characterised by short-pulse ablation of the metallic layer and vaporisation or degradation of the others due to thermal conduction from the former. At high velocity, all layers of the two films are ultimately removed by vaporisation or degradation as the average beam power is increased to achieve a complete cut. The transition velocity between the two characteristic removal types is shown to be a function of the pulse repetition rate. An experimental investigation validates the simulation results and provides new laser processing data for some typical packaging materials.
7
Seixas, Fabio Heredia. "Avaliação do uso do laser de Er: YAG sobre a remoção da camada de 'smear' das paredes dos canais radiculares com achatamento mésio-distal submetidos à instrumentação rotatória." Universidade de São Paulo, 2003. http://www.teses.usp.br/teses/disponiveis/58/58133/tde-19022004-120106/.
Full textAbstract:
No tratamento endodôntico, várias fases de igual importância são necessárias para a realização de uma terapêutica bem sucedida, entre elas podemos citar a instrumentação. Apesar de todas as técnicas e instrumentos propostos para a Endodontia, o sucesso esperado ainda não foi alcançado. Tanto a instrumentação manual quanto à rotatória não resulta na limpeza das áreas polares dos canais radiculares com achatamento mésio-distal. No intuito de obter melhor resultado clínico, avaliou-se in vitro a remoção da camada de smear das paredes dos canais radiculares de 40 dentes incisivos inferiores portadores de achatamento mésio-distal submetidos à instrumentação rotatória por meio da técnica Free Tip Preparation, utilizando o laser de Er: YAG nos parâmetros de 140 e 250 mJ. Para tanto, a fibra óptica do aparelho foi deslocada lentamente, com velocidade de 2 mm/s, até o orifício cervical na câmara pulpar, na parede vestibular e lingual da raiz; e sua eficácia na remoção da smear foi comparada aos grupos onde se utilizou apenas Hipoclorito a 2,5% e Hipoclorito de sódio a 2,5% alternado com EDTA a 17%. Os dentes foram analisados por meio de microscopia eletrônica de varredura, e as fotomicrografias das áreas mais representativas dos terços médio e apical foram avaliadas por três examinadores diferentes, com grau mínimo de Mestre, que observaram a quantidade da camada de smear presente nas amostras em relação a três padrões. Os examinadores, sem que tivessem o conhecimento prévio de qual dos grupos estavam avaliando, atribuíram escores de 1 a 4 as fotomicrografias, de acordo com a quantidade da camada de smear visualizada. Os dados obtidos foram submetidos à análise estatística não-paramétrica, comparando-se os diferentes grupos estudados (teste de Kruskal-Wallis) e os terços radiculares (teste de Wilcoxcon). Os resultados mostraram que, quanto à quantidade da smear encontrada nos grupos estudados, o grupo que utilizou Hipoclorito a 2,5% alternado com EDTA apresentou os canais radiculares mais limpos seguido do grupo do laser 250 mJ e posteriormente pelos grupos do laser Er: YAG a 140 mJ e do hipoclorito a 2,5%, que não apresentaram diferença estatisticamente significante entre si. Quanto aos terços, o apical apresentou maior quantidade da smear em comparação com o terço médio (p< 0,01).Manual or rotary instrumentation techniques do not efficiently clean mesio-distal flattened root canals. This study evaluated, in vitro, smear layer removal of 40 mesio-distal flattened root canals after rotary instrumentation. The teeth were then divided into 4 groups: group 1: rotary instrumentation and 2.5% sodium hypochlorite used as irrigating solution; group 2: instrumented as group 1 and followed by Er: YAG laser irradiation (140mJ input/10Hz), withdrawn at 2mm/s from the apical to the cervical region touching the buccal walls the procedure was then repeated for the lingual wall); group 3: instrumented as group 1 and followed by Er: YAG laser irradiation (250mJinput/10Hz) withdrawn at 2mm/s from the apical to the cervical region touching the buccal walls the procedure was then repeated for the lingual wall) and group 4: instrumented as group 1 and alternated with 17% EDTA Teeth were split longitudinally and prepared for examination under scanning electron microscopy. Scores from 1 to 4 were given to the fotomicrographs by three independent evaluators, and these data was submitted to statistical analysis. The teeth where alternated 17% EDTA were used (group 4) showed less amount of smear layer, followed by the group irradiated with 250mJinput/10Hz (group 3), the group irradiated with 140mJ input/10Hz and the group where only sodium hypochlorite was used. The apical third presented more smear layer than the middle third (p<00.1).
8
Campos, Zatarain Alberto. "Diode laser modules based on laser-machined, multi-layer ceramic substrates with integrated water cooling and micro-optics." Thesis, Heriot-Watt University, 2012. http://hdl.handle.net/10399/2595.
Full textAbstract:
This thesis presents a study on the use of low temperature co-fired ceramic (LTCC) material as a new platform for the packaging of multiple broad area single emitter diode lasers. This will address the recent trend in the laser industry of combining multiple laser diodes in a common package to reach the beam brightness and power required for pumping fibre lasers and for direct-diode industrial applications, such as welding, cutting, and etching. Packages based on multiple single emitters offer advantages over those derived from monolithic diode bars such as higher brightness, negligible thermal crosstalk between neighbouring emitters and protection against cascading failed emitters. In addition, insulated sub-mounted laser diodes based on telecommunication standards are preferred to diode bars and stacks because of the degree of assembly automation, and improved lifetime. At present, lasers are packaged on Cu or CuW platforms, whose high thermal conductivities allow an efficient passive cooling. However, as the number of emitters per package increases and improvements in the laser technology enable higher output power, the passive cooling will become insufficient. To overcome this problem, a LTCC platform capable of actively removing the heat generated by the lasers through impingement jet cooling was developed. It was provided with an internal water manifold capable to impinge water at 0.15 lmin-1 flow rate on the back surface of each laser with a variation of less than 2 °C in the temperature between the diodes. The thermal impedance of 2.7°C/W obtained allows the LTCC structure to cool the latest commercial broad area single emitter diode lasers which deliver up to 13 W of optical power. Commonly, the emitters are placed in a “staircase” formation to stack the emitters in the fast-axis, maintaining the brightness of the diode lasers. However, due to technical difficulties of machining the LTCC structure with a staircase-shaped face, a novel out-plane beam shaping method was proposed to obtain an elegant and compact free space combination of the laser beam on board using inexpensive optics. A compact arrangement was obtained using aligned folding mirrors, which stacked the beams on top of each other in the fast direction with the minimum dead space.
9
Shinpaugh, Kevin A. "Measurements in the bimodal region of a wing-body junction flow with a rapidly-scanning two-velocity-component laser-Doppler velocimeter." Diss., This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06062008-163435/.
Full text
10
YAGAMI, Hisanori, and Tomomi UCHIYAMA. "Numerical Simulation of Particle-Laden Plane Mixing Layer by Three-Dimensional Vortex Method." The Japan Society of Mechanical Engineers, 2006. http://hdl.handle.net/2237/9219.
Full text
11
Liu, Hao [Verfasser]. "Atomic layer deposition for high power laser applications: Al2O3 and HfO2 / Hao Liu." Hannover : Gottfried Wilhelm Leibniz Universität Hannover, 2018. http://d-nb.info/1174302542/34.
Full text
12
Crecelius, Anna Christina. "Thin layer chromatography-matrix assisted laser desorption ionisation-mass spectrometry of pharmaceutical compounds." Thesis, Sheffield Hallam University, 2002. http://shura.shu.ac.uk/19512/.
Full textAbstract:
Thin-layer chromatography (TLC) is of great importance for the pharmaceutical industry as a simple, quick, and low cost analytical method. Considerable effort has been made over the past decades to combine the simplicity of TLC with the selectivity and sensitivity of mass spectrometry (MS) detection. In the pharmaceutical industry sensitivity is an especially important factor, since the allowed impurity level of most drugs is under 0.1%.The aim of the present thesis was to develop methods for the direct examination of pharmaceutical compounds from TLC plates by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI TOF MS). The study was started by comparing several approaches for the application of the matrix for direct TLC-MALDI including a newly developed electrospray matrix deposition method. This new method was found to be superior to the other techniques studied. It produced a stable signal, minimised analyte spreading, and hence allowed the scanning of a TLC plate to obtain chromatographic as well as mass spectral data. The plotted mass chromatograms assisted in spot location, and allowed the calculation of Rf-values. These showed good agreement with the Rf -values determined by UV detection. The decrease in mass resolution and mass accuracy commonly observed in TLC-MALDI TOF MS due to the uneven nature of the silica gel layer was corrected by internal recalibration on selected matrix ions during the scanning of the TLC plate. To enhance the signals recorded directly from a TLC plate the use of an extraction solvent prior the matrix application was explored. Further improvements in sensitivity were obtained by modifying a robotic x-y-z axis motion system to act as an electrospray deposition device and by use of special Si 60 F[254] HPTLC-MALDI targets. Using both approaches sensitivities in the high fmol range were obtained. To minimise matrix interference, which can suppress analyte signals, the application of suspensions of particles of different materials and sizes (Co-UFP, TiN, TiO[2], graphite and silicon) onto eluted TLC plates were investigated. The structural analysis of pharmaceutical compounds was achieved by post-source decay - matrix-assisted laser desorption/ionisation (PSD-MALDI) mass spectrometry performed directly on the separated spots. TLC-MALDI MS is not only applicable to the qualitative analysis of pharmaceutical compounds. The generation of quantitative data by using a structural analogue as an internal standard is also described. Different approaches to the incorporation of the internal standard into the TLC plate were tested. The most successful approach was to develop the TLC plate in the mobile phase to which the internal standard was added. Good accuracy, precision, linearity and sensitivity was obtained using this approach.
13
Li, Ji. "A double layer-averaged model for stratified sediment-laden flow in open channels." Thesis, Heriot-Watt University, 2016. http://hdl.handle.net/10399/3205.
Full textAbstract:
Sediment-laden flows in open channels can be sharply stratified vertically, characterized by a double-layer flow structure composed of a subaqueous sediment-laden flow layer immediately over the bed and an upper clear-water flow layer. Typical examples include dam-break flows and reservoir sediment-laden flows featuring turbidity currents. In general, sharply stratified sediment-laden flows involve a number of physical factors, including sharp flow stratification, inter-layer exchange, active sediment transport, and substantial mass exchange with the bed. Double layer-averaged models are attractive in modelling such flows in connection to its vertical structure. However, existing double layer-averaged models have either partly or completely ignored the primary features of stratified open-channel sediment-laden flows and thus are not generally suitable. In the present thesis, a two-dimensional double layer-averaged model has been developed, explicitly incorporating the fundamental physical factors and therefore generally applicable for sharply stratified sediment-laden flows in open channels. First, the governing equations of the new model and the employed numerical algorithm are presented. Then, the model is applied to investigate mobile-bed dam-break flows due to instantaneous full dam break and progressive failure of a dike and landslide dams. Enhanced performance of the new model is demonstrated over the previous models. Most notably, it clearly justifies the physical necessity to incorporate sediment mass conservation. Next, the proposed model is applied to investigate reservoir sediment-laden flows featuring turbidity currents. The model is benchmarked against turbidity currents due to lock-exchange and sustained inflow. It is revealed that an appropriate clear-water outflow is favorable for turbidity current propagation, and also conducive to improving sediment flushing efficiency. As applied to prototype-scale turbidity current in the Xiaolangdi Reservoir in the Yellow River, China, the model successfully resolves the whole process from formation to recession. Following that, the hyperbolicity of the model equations is analyzed as related to dam-break flows and reservoir turbidity currents. The present model is demonstrated to preserve hyperbolicity and thus avoid Kelvin-Helmholtz instability. Computational tests for reservoir turbidity currents reveal that an excessive clear-water outflow would keep the turbidity current from being spoiled, and improves sediment flushing efficiency correspondingly.
14
Fawcett, Philip Andrew. "An investigation on planar velocimetry by spatial cross correlation." Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/15731.
Full text
15
Junior, Waldir Avansi. "Modificação e cristalização do sistema vítreo BaO-B2O3-RO2 (R=Ti, Si) utilizando a radiação de um laser de CO2." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-06052008-144955/.
Full textAbstract:
Este trabalho apresenta um estudo sobre a modificação e cristalização superficial dos sistemas vítreos 40BaO-45B2O3-15TiO2 (BBT) e 42BaO-42B2O3-16SiO2 (BBS) utilizando a radiação proveniente de um laser modulado de CO2. Três diferentes parâmetros experimentais foram avaliados: a potência do laser, o tempo de exposição à radiação e a presença de micropartículas da fase ?-BaB2O4 (?-BBO) na superfície da amostra. As modificações causadas pela exposição das amostras à radiação laser foram caracterizadas através das técnicas de perfilometria, microscopia óptica, espectroscopia micro-Raman e difração de raios X. De uma maneira geral, os resultados mostram que a escolha adequada da potência do laser e do tempo de exposição à radiação leva a uma modificação superficial ou a uma modificação seguida da cristalização superficial da região exposta a radiação. A presença de micropartículas da fase ?-BBO na superfície da amostras influi de maneira significativa no processo de modificação e cristalização superficial. A presença dessas micropartículas induziu a cristalização da fase ?-BBO com um relativo alto grau de orientação preferencial na direção (006), permitindo a observação visual do efeito de geração de segundo harmônico em algumas amostras. Estudos de micro-fotoluminescência mostraram que o íon Sm3+ quando adicionado a matriz vítrea BBT apresenta um alto grau de desordem mesmo em amostras cristalizadas. No entanto, para a matriz BBS, este estudo mostra uma possível incorporação do íon terra-rara na região cristalizada.This work describes a study regarding the permanent modification and/or crystallization of 40BaO-45B2O3-15TiO2 (BBT) and 40BaO-45B2O3-16SiO2 (BBS) glass compositions when exposed to a continuous CO2 laser beam radiation. The effect of three experimental parameters was evaluated: the laser power, the radiation time exposure and the presence of micro-particles of the ?-BaB2O4 crystalline phase on the glass sample surface prior to radiation. The geometry of permanent modification and the crystallization process were characterized by using the perfilometry, optical microscopy, Micro-Raman spectroscopy and X-ray diffraction (XRD) techniques. The results show that the surface modification and crystallization can be controlled by a suitable choice of the laser power and radiation time exposure. In all samples, it was observed that the presence of ?-BaB2O4 micro-particles on the sample surface affects significantly equally the permanent modification and the crystallization process. The preferential orientation of the ?-BaB2O4 on the (006) plane direction allowed the observation of a relative high intense second harmonic generation effect. The micro-photoluminescence study shows that the Sm3+ ion in BBT glass sample present a high degree of disorder, even in the crystallized samples. On the other hand, when added to the BBS glass sample, it seems that the Sm3+ ions are incorporated onto the crystallized region.
16
Silva, Patrícia Rondon Pleffken da [UNESP]. "Estudo das propriedades mecânicas da interface adesiva criada por sistemas adesivos convencional e autocondicionante, associados ou não ao laser Nd:YAG, utilizando a técnica da nanoindentação." Universidade Estadual Paulista (UNESP), 2010. http://hdl.handle.net/11449/89588.
Full textAbstract:
Made available in DSpace on 2014-06-11T19:24:07Z (GMT). No. of bitstreams: 0
Previous issue date: 2010-07-05Bitstream added on 2014-06-13T19:51:19Z : No. of bitstreams: 1
silva_prp_me_sjc.pdf: 750069 bytes, checksum: 94263aef7c378118e8087ea9d933ad86 (MD5)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
O objetivo desta pesquisa foi avaliar a influência do laser Nd:YAG nas propriedades mecânicas (dureza e módulo de elasticidade) da interface adesiva, utilizando a técnica da nanoindentação, empregando-se sistema adesivo convencional Adper Single Bond 2 – 3M ESPE (SB) ou autocondicionante Clearfil SE Bond – Kuraray (CSE). Doze terceiros molares humanos tiveram suas superfícies oclusais desgastadas até a exposição da dentina superficial. Uma cavidade circular padronizada com fresa 3053 foi realizada na superfície oclusal proporcionando 2 mm de dentina remanescente. Os espécimes foram embutidos em resina acrílica, e seccionados no sentido mésio-distal, sendo as 24 hemi-coroas obtidas divididas em quatro grupos: Grupo controle (SBC) - aplicação do sistema SB de acordo com as recomendações do fabricante; Grupo laser (SBL) - aplicação do sistema adesivo SB e tratamento com laser Nd:YAG (140mJ/cm2/60s/não contato); Grupo controle (CSEC) - aplicação do sistema adesivo autocondicionante CSE de acordo com as recomendações do fabricante; Grupo laser (CSEL)- aplicação do sistema adesivo autocondicionante CSE e tratamento com laser Nd:YAG (140mJ/cm2/60s/não contato). Após a polimerização dos sistemas adesivos, foram aplicados dois incrementos da resina composta Filtek Z 350 (3M ESPE). Os corpos-de-prova foram imersos em água destilada e armazenados por 24h em estufa 37ºC e submetidos à nanoidentação em aparelho Nano Indenter® XP (MTS®, MN, EUA).. Os resultados foram submetidos aos testes estatísticos de Análise de Variância (ANOVA), Tukey e t-Student (p<0,05). Concluiu-se que a aplicação do laser Nd:YAG em ambos os sistemas adesivos não alterou o nível de dureza da interface adesiva, no entanto alterou o módulo de elasticidade
The aim of this study was to evaluate the influence of Nd: YAG laser on the mechanical properties (hardness and modulus of elasticity) of the adhesive interface, using the technique of nanoindentation, employing conventional adhesive system Single Bond 2 3M ESPE (SB) or selfetching adhesive system Clearfil SE Bond - Kuraray (CSE). On 12 human molars, a flat superficial dentin surface was exposed by abrasion. A standardized circular cavity with bur 3053 was performed on the occlusal surface and dentin thickness was standardized in 2 mm. The specimens were embedded in resin acrylic and sectioned mesio-distally through their long axes, and the 24 hemi-crowns obtained divided into four groups: Control Group (SBC) – the application of SB system according to the manufacturer's recommendations; Laser Group (SBL) – SB adhesive system and treatment with Nd: YAG laser (140mJ/cm2/60s/no contact) Control Group (CSEC) – application of CSE self-etching adhesive system according to the manufacturer's recommendations; Laser Group (CSEL) – application of CSE self-etching adhesive system and treatment with Nd: YAG laser (140mJ/cm2/60s/no contact). After polymerization of the adhesives, were applied two increments of composite resin Filtek Supreme and specimens were immersed in distilled water and stored for 24 hours at 37 ºC and submitted to nanoidentation in Nano Indenter ® XP (MTS ®, MN, USA. Nanoindentation were made on composite resin, adhesive system, hybrid layer and dentin. The results were analyzed by a tree-way ANOVA, Tukey and e t-Students (p<0,05). It was concluded that the application of Nd:YAG laser in both adhesive systems did not change hardness level of hybrid layer, however chanded the elastic modulus
17
Monk, John Lawrence III. "Theoretical Study of Semiconductor Quantum Dot Lasers with Asymmetric Barrier Layers." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/98524.
Full textAbstract:
Small-signal dynamic response of semiconductor quantum dot (QD) lasers with asymmetric barrier layers was studied. Semiconductor lasers are used in many communication systems. Fiber optic communication systems use semiconductor lasers in order to transmit information. DVD and Blu-ray disk players feature semiconductor lasers as their readout source. Barcode readers and laser pointers also use semiconductor lasers. A medical application of semiconductor lasers is for minor soft tissue procedures. Semiconductor lasers are also used to pump solid-state and fiber lasers. Semiconductor lasers are able to transmit telephone, internet, and television signals through fiber optic cables over long distances. The amount of information able to be transferred is directly related to the bandwidth of the laser. By introducing asymmetric barrier layers, the modulation bandwidth of the laser will improve, allowing for more information to be transferred. Also, by introducing asymmetric barrier layers, the output power will be unrestricted, meaning as more current is applied to the system, the laser will get more powerful. An optimum pumping current was found which maximized modulation bandwidth at -3dB, and is lower in QD lasers with asymmetric barrier layers (ABL) as opposed to conventional QD lasers. Modulation bandwidth was found to increase with cross section of carrier capture before reaching an asymptote. Both surface density of QDs and cavity length had optimum values which maximized modulation bandwidth. Relative QD size fluctuation was considered in order to see how variation in QD sizes effects the modulation bandwidth of the semiconductor QD laser with ABLs. These calculations give a good starting point for fabricating semiconductor QD lasers with ABLs featuring the largest modulation bandwidth possible for fiber optic communication systems.
In semiconductor QD lasers, the electrons and holes may be captured into excited states within the QDs, rather than the ground state. The particles may also jump from the ground state up to an excited state, or drop from the excited state to the ground state. Recombination of electron-hole pairs can occur from the ground state to the ground state or from an excited state to an excited state. In the situation if the capture of charge carriers into the ground state in QDs takes place via the excited-state, then this two-step capture process makes the output power from ground-state lasing to saturate in conventional QD lasers. By using ABLs in the QD laser, it is predicted that the output power of ground-state lasing will continue to rise with applied current, as the ABLs will stop the electrons and holes from recombining in the optical confinement layer. Thus, ABL QD lasers will be able to be used in applications that require large energy outputs.Master of Science
Semiconductor lasers (also known as diode lasers) have been used in numerous applications ranging from communication to medical applications. Among all applications of diode lasers, of particular importance is their use for high speed transmission of information and data in fiber optic communication systems. This is accomplished by direct conversion of the diode laser input (electrical current) to its output (optical power). Direct modulation of the laser optical output through varying electrical current helps cut costs by not requiring other expensive equipment in order to perform modulation. The performance of conventional semiconductor lasers suffers from parasitic recombination outside of the active region – an unwanted process that consumes a considerable fraction of the laser input (injection current) while not contributing to the useful output and thus damaging its performance. Asymmetric barrier layers were proposed as a way to suppress parasitic recombination in semiconductor lasers. In this study, the optimal conditions for semiconductor quantum dot lasers with asymmetric barrier layers were calculated in order to maximize their modulation bandwidth – the parameter that determines the highest speed of efficient information transmission. This includes finding the optimal values of the dc component of the pump current, quantum dot surface density and size fluctuations, and cavity length. As compared to conventional quantum dot lasers, the optimal dc current maximizing the modulation bandwidth is shown to be considerably lower in quantum dot lasers with asymmetric barrier layers thus proving their outperforming efficiency. In the presence of extra states in quantum dots in conventional lasers, the optical output of needed ground-state lasing may be heavily impacted – it may remain almost unchanged with increasing the laser input current. As opposed to conventional lasers, the output power of ground-state lasing in devices with asymmetric barrier layers will continue growing as more input current is applied to the system.
18
Capelli, Alexandre. "Avaliação in vitro da remoção da camada residual (smear layer) de canais radiculares achatados instrumentados com quatro diferentes sistemas rotatórios com e sem associação de ultra-som e laser ER:YAG." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/58/58133/tde-01042008-084424/.
Full textAbstract:
Estudou-se, por meio da microscopia eletrônica de varredura, a remoção da \"smear layer\" dos canais radiculares preparados com sistemas rotatórios com e sem \"radial land\". Após a preparação, as paredes dos canais radiculares foram submetidas aos tratamentos com ultra-som, aplicação do agente quelante EDTA a 15% e do laser Er:YAG. Noventa e seis incisivos inferiores humanos foram selecionados e divididos aleatoriamente em quatro grupos distintos, preparados com técnica rotatória Free Tip (Pecora et al, 2002) com instrumentos de níquel-titânio, 0,5 mm aquém do ápice anatômico, variando-se apenas o tratamento final das paredes do canal radicular. No grupo 1 utilizou-se o hipoclorito de sódio a 2,5% durante a instrumentação; no grupo 2 realizou-se irrigação com hipoclorito de sódio a 2,5% durante a instrumentação, recebendo posteriormente irradiação com laser Er:YAG (KaVo Key Laser II), com o auxílio de uma fibra óptica 30/28 de 285 µm de diâmetro, gerando uma energia total de 42 J, freqüência de 15 Hz e potencia de 250mJ input (140mJ output). A cinemática utilizada na irradiação foi de movimento helicoidal de tração da fibra óptica, de apical para cervical, durante 10 segundos, sendo repetida quatro vezes; no grupo 3 utilizou-se a solução de hipoclorito de sódio a 2,5% ativada pelo ultra-som (MiniPiezon, EMS, Suíça); no grupo 4 utilizou-se a solução de hipoclorito de sódio a 2,5% e irrigação final com EDTA a 17%. Os espécimes foram preparados para microscopia eletrônica de varredura, e as fotomicrografias obtidas dos terços médio e apical submetidas a avaliação qualitativa por três observadores previamente calibrados, que atribuíam escores as imagens. A análise estatística revelou que a presença ou ausência da superfície radial de apoio (radial land) não interferiu na limpeza das paredes dos canais radiculares. Com relação ao tratamento final, o EDTA a 15% foi capaz de eliminar a \"smear layer\" com maior eficácia, sendo seguido pelo ultra-som e finalmente o laser Er:YAG. Houve diferença estatística significante entre os terços médio e apical dos canais radiculares.This study evaluated, in vitro, smear layer removal in apical and middle root thirds after instrumentation with four different rotary Ni-Ti instruments and the use of Er:YAG laser, ultrasonic or EDTA. Nineth six mandibular incisors root canals were instrumented with Free Tip Technique, and irrigated with 10 ml of sodium hypochlorite. In Group 1, 24 teeth were instrumented and irrigated only with 10 ml of 2.5 % sodium hypochlorite. Group 24, instrumented as group 1 and irradiated laser Er:YAG in the following parameters: 30/28 fiber optic tip, 42 J, 15Hz and 250mJ input (140mJ output), with the tip activated at the apex and removed to the canal entrance in a helicoidal moviment. Group 3, instrumented as in group 1 and associated with ultrasonic. Group 4, instrumented as in group 1 and associated with with 15% EDTA. Electronic Microscope images were evaluated showed that group 4 had significantly less smear layer (p<0,05) than the group 1 and 2, with group 3 in intermediated position. We conclude that sodium hypochlorite associated with 15% EDTA lead to root canals with less smear layer. The middle third present less smear layer than apical third.
19
Blanquer, Eric. "LADAR Proximity Fuze - System Study -." Thesis, KTH, Reglerteknik, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-106247.
Full textAbstract:
LADAR (Laser Detection and Ranging) systems constitue a direct extension of the conventional radar techniques. Because they operate at much shorter wavelengths, LADARs have the unique capability to generate 3D images of objects. These laser systems have many applications in both the civilian and the defence fields concerning target detection and identification. The extraction of these features depends on the processing algorithms, target properties and 3D images quality. In order to support future LADAR hardware device developments and system engineering studies, it is necessary to understand the influences of the phenomena leading to the final image. Hence, the modelling of the laser pulse, propagations effects, reflection properties, detection technique and receiver signal processinghave to be taken into account. A complete simulator has been developed consisting of a graphical user interface and a simulation program. The computer simulation produces simulated 3D images for a direct detection pulse LADAR under a wide variety of conditions. Each stage from the laser source to the 3D image generation has been modelled. It yields an efficient simulation tool which will be of help in the design of the future LADAR systems and gauge their performances. This master’s thesis contains the theoretical background about laser used to build the simulation program. The latter is described schematically in order to provide an insight for the reader. The graphical interface is then presented as a short user’s manual. Finally, in order to illustrate the possibilities of the simulator, a collection of selected simulations concludes the report.
20
Roberts, Ibiye Aseibichin. "Investigation of residual stresses in the laser melting of metal powders in additive layer manufacturing." Thesis, University of Wolverhampton, 2012. http://hdl.handle.net/2436/254913.
Full textAbstract:
Laser Melting (LM) is an Additive Layer Manufacturing (ALM) process used to produce three-dimensional parts from metal powders by fusing the material in a layerby- layer manner controlled by a CAD model. During LM, rapid temperature cycles and steep temperature gradients occur in the scanned layers. Temperature gradients induce thermal stresses which remain in the part upon completion of the process (i.e. residual stresses). These residual stresses can be detrimental to the functionality and structural integrity of the built parts. The work presented in this thesis developed a finite element model for the purpose of investigating the development of the thermal and residual stresses in the laser melting of metal powders. ANSYS Mechanical software was utilised in performing coupled thermal-structural field analyses. The temperature history was predicted by modelling the interaction of the moving laser heat source with the metal powders and base platform. An innovative ‘element birth and death’ technique was employed to simulate the addition of layers with time. Temperature dependent material properties and strain hardening effects were also considered. The temperature field results were then used for the structural field analysis to predict the residual stresses and displacements. Experiments involving laser melting Ti-6Al-4V powder on a steel platform were performed. Surface topography analyses using a laser scanning confocal microscope were carried out to validate the numerically predicted displacements against surface measurements. The results showed that the material strain hardening model had a direct effect on the accuracy of the predicted displacement results. Using the numerical model, parametric studies were carried out to investigate the effects of a number of process variables on the magnitude of the residual stresses in the built layers. The studies showed that: (i) the average residual stresses increased with the number of melted powder layers, (ii) increasing the chamber temperature to 300°C halved the longitudinal stresses. At 300°C, compressive stresses appeared on the Ti64 surface layer, (iii) reducing the raster length from 1 mm to 0.5 mm reduced the average longitudinal stress in the top layer by 51 MPa (0.04σy), (iv) reducing the laser scan speed from 1200 mm/s to 800 mm/s increased the longitudinal stress by 57 MPa (0.05σy) but reduced the transverse stress by 46 MPa (0.04σy).
21
LIMA, Grasiele Assis da Costa. "Capacidade de remoção do SMEAR LAYER dos canais radiculares com o uso do ultrassom, CANALBRUSH™ E LASER Nd: YAG através da microscopia eletrônica de varredura." Universidade Federal de Pernambuco, 2013. https://repositorio.ufpe.br/handle/123456789/13057.
Full textAbstract:
Submitted by Leonardo Freitas (leonardo.hfreitas@ufpe.br) on 2015-04-13T14:36:36Z
No. of bitstreams: 2
Dissertaçao Grasiele Lima.pdf: 1061882 bytes, checksum: 1363fae0620e5a9f063191ea45f4d653 (MD5)
license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5)Made available in DSpace on 2015-04-13T14:36:37Z (GMT). No. of bitstreams: 2 Dissertaçao Grasiele Lima.pdf: 1061882 bytes, checksum: 1363fae0620e5a9f063191ea45f4d653 (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Previous issue date: 2013-02-22
CNPq
Objetivo: comparar a eficiência do Ultrassom, CanalBrush™ e LASER, associado ao EDTA 17%, na remoção de smear layer no terço apical dos canais radiculares. Metodologia: 50 raízes distais de primeiros molares inferiores humanos com processo de rizogênese concluído foram submetidas ao preparo biomecânico utilizando o Sistema ProTaper Universal™ até a lima F5. Os espécimes foram divididos em 5 grupos (n= 10) e submetidos a uma irrigação final com EDTA e diferentes técnicas de agitação: controle negativo, limas ProTaper Universal™, Ultrassom, CanalBrush™ e LASER. Após esse procedimento, os espécimes foram clivados e foram obtidas imagens a partir do microscópio eletrônico de varredura. As imagens foram analisadas e foi atribuído um escore a cada espécime. Os dados foram tabulados e submetidos à análise estatística através dos testes de Kruskal Wallis e de Mann-Whitney com nível de significância de 5%. Resultados: o ultrassom apresentou remoção completa de smear layer em 56,6% dos espécimes e obteve diferença estatisticamente significativa em relação aos demais grupos (p< 0,005). O LASER obteve remoção completa de smear layer em 30% dos espécimes com resultado inferior ao do ultrassom. O Canalbrush™ e a lima ProTaper Universal™ não mostraram diferença estatisticamente significante entre si (p= 0,321); ambos os grupos não obtiveram nenhum espécime com remoção completa de smear layer. Conclusões: o uso do EDTA contribuiu para a remoção da smear layer. O ultrassom apresentou melhor desempenho, seguido do LASER. Porém, nenhuma técnica foi capaz de remover a smear layer totalmente.
22
Morris, T. J. "An experimental Rayleigh laser guide star ground layer adaptive optics system for the William Herschel telescope." Thesis, Durham University, 2005. http://etheses.dur.ac.uk/2717/.
Full textAbstract:
The design of an experimental ground layer adaptive optics (GLAO) system that uses a low altitude Rayleigh laser guide star as a wavefront reference source is presented. GLAO is a technique for achieving wide-field partial adaptive optics correction of the aberrations in a wavefront due to the effects of propagation through a turbulent atmosphere. The theoretical performance of the GLAO sub-systems, such as the laser launch system, wavefront sensor and optical train are analysed and compared, where possible, to measurements taken both under laboratory conditions and on-sky at the William Herschel Telescope.
23
Chen, Sophia Nan. "X-ray spectroscopy of buried layer foils irradiated with an ultra high intensity short pulse laser." Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3352706.
Full textAbstract:
Thesis (Ph. D.)--University of California, San Diego, 2009.Title from first page of PDF file (viewed June 16, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 117-126).
24
Conrad, Ross Aaron. "Impact of the boundary layer on pointing and tracking in airborne free-space laser communication links." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44929.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes vita.
Includes bibliographical references (p. 117-118).
Free-space laser communication is a developing technology with enormous potential to revolutionize the way people communicate across the globe. Of specific interest are air-to-space lasercom links. Such a link experiences atmospheric scintillation, platform jitter, and boundary layer turbulence. This research investigated the tracking challenge using a focal plane array sensor with centroid and peak tracking algorithms. Also investigated was the use of a deformable mirror to recreate optical phase distortions from boundary layer turbulence. Experiments were conducted with realistic channel effects for multiple look angles between a subsonic aircraft at 29 kft and geosynchronous satellite. Performance was determined by power delivered to an optical fiber. The results show that the two tracking algorithms can differ by up to one decibel of fiber power, with centroid tracking generally performing best. Conclusions are highly dependent on aircraft and spacecraft parameters but point towards centroid tracking for maximizing received power. Keywords: Lasercom, FPA Tracking, Boundary Layer Disturbances, Deformable Mirror.
by Ross Aaron Conrad.
S.M.
25
Raghavan, Satyanarayanan. "Laser-based hybrid process for machining hardened steels." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/47550.
Full textAbstract:
Cost-effective machining of hardened steel (>60 HRC) components such as a large wind turbine bearing poses a significant challenge. This thesis investigates a new laser tempering based hybrid turning approach to machine hardened AISI 52100 steel parts more efficiently and cost effectively. The approach consists of a two step process involving laser tempering of the hardened workpiece surface followed by conventional machining at higher material removal rates using lower cost ceramic tooling to efficiently cut the laser tempered material.
The specific objectives of this work are to: (a) study the characteristics of laser tempering of hyper-eutectoid 52100 hardened steel, (b) model the laser tempering process to determine the resulting hardness, and (c) conduct machining experiments to evaluate the performance of the laser tempering based hybrid turning process in terms of forces, tools wear and surface finish.
First, the microstructure alterations and phase content in the surface and subsurface layers are analyzed using metallography and x-ray diffraction (XRD) respectively. Laser tempering produces distinct regions consisting of - a tempered white layer and a dark layer- in the heat affected subsurface region of the workpiece. The depth of the tempered region is dependent on the laser scanning conditions. Larger overlap of laser scans and smaller scan speeds produce a thicker tempered region. Furthermore, the tempered region is composed of ferrite and martensite and weak traces of retained austenite (~ 1 %).
Second, a laser tempering model consisting of a three dimensional analytical model to predict the temperature field generated by laser scanning of 52100 hardened steel and a phase change based hardness model to predict the hardness of the tempered region are developed. The thermal model is used to evaluate the temperature field
induced in the subsurface region due to the thermal cycles produced by the laser scanning step. The computed temperature histories are then fed to the phase change model to predict the surface and subsurface hardness. The laser tempering model is used to select the laser scanning conditions that yield the desired hardness reduction at the maximum depth. This model is verified through laser scanning experiments wherein the hardness changes are compared with model predictions. The model is shown to yield predictions that are within 20 % of the measured hardness of the tempered region.
Using the laser scanning parameters determined from the laser tempering model, cutting experiments using Cubic Boron Nitride (CBN) tools and low cost alumina ceramic tools are conducted to compare the performance of laser tempering based hybrid turning with the conventional hard turning process. The machining experiments demonstrate the possibility of higher material removal rates, lower cutting forces, improved tool wear behavior, and consequently improved tool life in the laser tempering based process. In addition, the laser tempered based hybrid turning process produce is shown to yield lower peak-to-valley surface roughness height than the conventional hard turning process. Furthermore, it is found that lower cost ceramic tools can be used in place of CBN tools without compromising the material removal rate.
26
García, Vizcaino David. "Sistema láser de medida de velocidad por efecto doppler de bajo coste para aplicaciones industriales e hidrodinámicas." Doctoral thesis, Universitat Politècnica de Catalunya, 2005. http://hdl.handle.net/10803/6892.
Full textAbstract:
La utilización práctica del efecto Doppler en la emisión láser fue propuesta desde los inicios del desarrollo de los láseres en los años sesenta. Sólo en los años ochenta la investigación realizada pudo salir del laboratorio y dar lugar a la fabricación de aparatos de medida de velocidad comerciales. A partir de los noventa estos aparatos se popularizaron rápidamente. Actualmente se utilizan medidores de velocidad láser por efecto Doppler en múltiples aplicaciones, entre las que sobresale la medida de velocidad de fluidos, para estudios aéreo e hidrodinámicos. Sus características únicas, como la precisión obtenida en la medida, su alta resolución espacial y el carácter no intrusivo, sólo han comenzado recientemente a tener rivales de consideración, como pueden ser la velocimetría de imagen de partículas (PIV). También la medida de velocidades de móviles sólidos comienza a resultar, con el abaratamiento general de los componentes opto-electrónicos, un objetivo para muchas empresas. Entre las aplicaciones de este tipo se contemplan el control de velocidad de los vehículos en carretera y el control de procesos industriales del ramo textil, papelero y deempresas fabricantes de cables, entre otros.
Empresas europeas y americanas, como Dantec Electronik y TSI, por citar las más representativas, comercializan aparatos LDA de propósito general de altas prestaciones. Hasta la fecha estos sistemas sólo podían ser adquiridos por importantes centros de investigación o grandes empresas, debido a su elevado coste. El futuro comercial de la velocimetría láser Doppler exige la fabricación de aparatos más económicos y adaptados a las necesidades del cliente. Muchos de los sistemas actuales son voluminosos,
difíciles de manejar y con potencias de trabajo elevadas. Se está llevando a cabo un importante trabajo para conseguir reducir el tamaño y coste de los equipos sin perder sus principales prestaciones. Asimismo la alta velocidad y capacidad de cálculo de los ordenadores personales actuales debe hacer innecesaria la inclusión de procesadores específicos para estos equipos.
Presentamos el diseño y construcción de un sistema integral de medida de dos componentes de la velocidad, sistema 2D-LDA, para aplicaciones industriales e hidrodinámicas de baja potencia.
Siguiendo la filosofía delineada arriba, el diseño de nuestro sistema LDA fue realizado utilizando únicamente una fuente laser y un módulo detector. Los sistemas LDA de medida de dos componentes de velocidad comercialmente disponibles, por el contrario, emplean dos longitudes de onda óptica y dos fotodetectores independientes. Las emisiones azul y verde típicas de los láseres de ion-Ar son las longitudes de onda a menudo elegidas en este tipo de medidas.
Por otra parte, se ha empleado los dos canales de entrada de una tarjeta de adquisición de uso general para realizar el disparo multinivel. Esta configuración permite trabajar en cada momento con la parte de señal burst teóricamente más adecuada, con mayor valor de relación señal a ruido.
Este trabajo ha sido financiado por la CICYT Proyecto PETRI 95-0249-OP:
REALIZACIÓN DE SISTEMAS LÁSER PORTÁTILES DE MEDIDA DE VELOCIDAD POR EFECTO DOPPLER (LDA-LDV) DE BAJO COSTE PARA APLICACIONES INDUSTRIALES E HIDRODINÁMICAS.
The practical use of the Doppler effect at optical wavelengths was proposed at the early beginning of the development of the laser, in the sixties. However, it was only in the eighties when the results of the experimental work could finally get out of the laboratories, and the first Laser Velocimeters were commercially available. In the nineties this kind of systems became rapidly popular. Nowadays the Laser Velocimeters based on the Doppler frequency shift find a lot of important applications, especially in some industrial processes and in hydrodynamic and aerodynamic research.
The unique characteristics of the Laser Doppler Velocimetry (LDV) only recently have encountered a rival technique in the Particle Image Velocimetry (PIV), for applications on fluids. The main features of LDV systems are the accuracy and the speed of the measurements, the high spatial resolution and, of course, the non-intrusive character of the technique. Moreover this kind of systems present advantages not only in fluid applications: actually it can compete with the microwave radar in the estimation of the velocity of solid targets. This becomes possible due to the
progressive reduction of prices of optoelectronic devices and the improvement of its performances. The monitoring of the traffic velocity and the control of machinery in the manufacture of paper, wires and cables or thread can be mentioned among these applications.
European an American companies, as Dantek Electronic or TSI, to mention the two most representative, commercialize high performance general-purpose LDV systems. Up to the date these instruments are sizeable and expensive, and its use requires some special training. There is not doubt that the future market of the LDV systems goes through a substantial decrease of prices and, indeed, through the possibility of custom-built designs. The potential number of users would increase then in an important manner. Many efforts are now being devoted by researchers in that direction. Moreover, the important improvement of capabilities of the desktop computers makes unnecessary the special electronic processors that, up to now, have been provided by the manufacturers of LDV systems as a part of them.
In this Thesis the design and realization of a complete Laser Doppler Anemometer is presented. The system can measure two components of a fluid velocity (2D-LDA) and originally it was conceived to be used in industrial and hydrodynamics applications.
Following the philosophy outlined above, the design of our LDA system was performed with only one laser source and one detector module. The common commercially available LDAs, on the contrary, designed to measure two components of velocity, use two different optical wavelengths and two independent photodiodes.
On the other hand, a general-purpose acquisition card with two input channels has been used to implement a multilevel trigger. The configuration performed here permits to work in each moment with the part of the burst having the best signal to noise ratio.
This work has been supported by the Spanish Government, CICYT project PETRI 95-0249-OP.
27
Jurin, Florian. "Croissance et propriétés de films minces conducteurs par auto-assemblage de polyélectrolytes." Thesis, Besançon, 2014. http://www.theses.fr/2014BESA2072/document.
Full textAbstract:
L'auto-assemblage de polymères a été étudié afin d'élaborer des films multicouches possédant des propriétés conductrices. Dans un premier temps, l'influence de différents paramètres physico-chimiques (pH , force ionique, nature et charge des ions, concentrations en polymères...) sur la croissance de couche polymères isolants (PSS ou PDDA) / polymères conducteurs ( PEDOT : PSS ou P3HT-R) a été étudiée par des mesures in-situ de réflectométrie laser à angle fixe. La compréhension de ses paramètres a permis de contrôler l'assemblage des matériaux afin d'obtenir des films multicouches aux propriétés souhaitées ( épaisseur, morphologie, conductivité électrique...)les épaisseurs des films obtenus ont été déterminées par ellipsométrie ou profilométrie, la morphologie de la morphologie de la surface de ces films a été observé par MEB et leur conductivité a été mesurée par la méthode de van Pauw. Dans un second temps, des films multicouches polymères / particules composites ont été construits après avoir optimisé les conditions d'élaboration des particules composites Al2-PEDOT : PSSph ou SiO2-P3HT-R).Les films multicouches obtenus présentent des conductivités équivalentes à celles des films à base de polymères mais sont construits avec moins d'étapes d'adsorption. Enfin des couches multicouches à bases de deux polymères conducteurs (P3HT-R et PEDOT:PSS) ont été construits sur substrats souples. Ils présentent la plus haute conductivité mesurée (1,5 S.m-1) et conservent leurs propriétés électriques lorsqu'ils sont soumis à des contraintes mécaniques de flexion , ce qui est prometteur quant à leur utilisation dans le domaine de l'électronique déformableSelf-assembly of polymers has been studied in order to produce multilayer films having conductive properties. First, the influence of various physicochemical parameters (pH, ionic strength, nature and charge of ions, polymer concentrations, etc.) on the growth of insulating polymer (PSS or PDDA) / conductive polymers (PEDOT : PSS or P3HT-R) was studied by in-situ measurements of fixed-angle laser reflectometry. The understanding of its parameters allowed to control the assembly of the materials in order to obtain multilayer films with the desired properties (thickness, morphology, electrical conductivity...) The thicknesses of the films obtained were determined by ellipsometry or profilometry, morphology Of the surface morphology of these films was observed by SEM and their conductivity was measured by the method of van Pauw. Second, polymer multilayer films / composite particles were built after optimizing the conditions for the production of the composite particles Al2-PEDOT: PSSph or SiO2-P3HT-R). The multilayer films obtained have conductivities equivalent to those of Films are based on polymers but are constructed with fewer adsorption steps. Finally, multilayer layers based on two conductive polymers (P3HT-R and PEDOT: PSS) were built on flexible substrates. They have the highest conductivity measured (1.5 Sm-1) and retain their electrical properties when subjected to mechanical bending stresses, which is promising for their use in the field of deformable electronics
28
Carvalho, Luisa. "Etude de l’interaction laser surface pour le développement de procédé de décontamination de surfaces métalliques avec fissures micrométriques par ablation laser." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS462/document.
Full textAbstract:
En réponse aux opérations futures d’assainissement des installations nucléaires, la décontamination par ablation laser de surfaces métalliques apparait comme une technique adaptée aux enjeux sanitaires et économiques actuels. L’objectif est d’ablater par un faisceau laser de façon préférentielle la surface oxydée contenant des radioéléments et de récupérer les éléments vaporisés pour pouvoir isoler la contamination radioactive en vue de son stockage. A la différence des techniques existantes comme le ponçage ou le traitement chimique par gel ou mousse, le traitement laser permet de ne pas produire de déchets secondaires et de pouvoir être effectué à distance en diminuant considérablement la dose reçue par les opérateurs. Le retour d’expérience a montré la nécessité d’optimiser le procédé en vue de limiter la contamination résiduelle. Les phénomènes responsables de cette limitation et identifiés dans la littérature sont la pénétration des contaminants dans le substrat métallique par effet thermiques induits par laser et le piégeage des radionucléides dans des défauts de surface micrométriques. Les travaux de thèse auront donc comme objectifs d’étudier et d’optimiser la décontamination de surfaces métalliques avec des couches d’oxydes contaminées de façon volumique avec un simulant de radionucléide (Eu) par ablation laser, en vue dans un second temps d’améliorer de l’efficacité de la technique au niveau des défauts surfaciques. Enfin, au-delà de la démarche expérimentale, cette thèse vise à contribuer à la compréhension de l’interaction laser/matière dans le cadre de notre étude via la simulation du chauffage de surface métallique par modélisation multi physiqueThe preparation of future decommissioning of nuclear installations is currently facing economical and sanitary challenges. The metallic-surface decontamination by laser ablation is here studied as an appropriate and efficient technique, which involves ejection of surface contamination by subjecting the surface to high-energy laser pulses followed by subsequent trapping to avoid environmental dispersion. This process has many advantages such as the minimization of secondary waste, no production of effluents and the reduction of the exposition of workers by the automation of the process. Previous studies highlighted the need to optimize the process in order to limit the residual contamination. The identified reasons for this limitation are the contamination penetration into the metal bulk induced by the laser treatment and the entrapment of the radionuclides in surface defects like micro cracks. The aim of this work is the study and the cleaning optimization of metallic surfaces with an oxide layer implemented with a non-radioactive contamination (Eu). Secondly, the cleaning efficiency has been improved in case of damaged surfaces with defects such as cracks. Beyond an experimental study, The ablation of a metallic substrate with a submicrometric oxide layer is currently modeled using a numerical and multiphysics approach in order to determine the mechanism involved during the process
29
Ailinger, Kevin Gerard. "Measurements of surface shear stresses under a three-dimensional turbulent boundary layer using oil-film laser interferometry." Thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-11012008-063040/.
Full text
30
Rolon, Juan Carlos. "Etude théorique et expérimentale de la flamme de diffusion à contre-courant." Châtenay-Malabry, Ecole centrale de Paris, 1988. http://www.theses.fr/1988ECAP0102.
Full textAbstract:
Caractérisation de la flamme de diffusion à contre-courant par techniques de diagnostic laser : vélocimétrie laser Doppler et déviation d'un faisceau laser diode laser. Présentation de deux modèles théoriques de combustion en chimie simple dans l'approximation de la couche monodimensionnelle
31
Brehovský, Patrik. "Svařování hlubokotažných ocelí s ochrannou vrstvou hybridní technologií Laser-TIG." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2020. http://www.nusl.cz/ntk/nusl-417119.
Full textAbstract:
The diploma thesis focuses on laser welding of extra deep-drawn steel sheet according to the standard WSS-M1A365-A14 with a protective zinc surface layer. A 0,9 mm thick steel sheet with a zinc layer with coating weight 50 g · m^-2 is welded by a hybrid welding method Laser-TIG. The laser, as the primary energy source, is used for welding the material. The arc, provided by a non-melting tungsten electrode, is used for preheating the material for melting and evaporation of the zinc layer. Based on the initial experiments, the magnitude of the laser power with the welding speed was chosen as a constant parameter. The magnitude of the electric current, as the variable parameter, was set up to 0, 20, 30 and 40 ampers for welding the lap and the butt welds. Only one piece of the each weld type combination was made. The welds were afterwards tested to verify their quality and material properties. The first differences between laser welding with or without TIG preheating were visible during the experiment. The positive effects of the laser welding with preheating by TIG were confirmed. The material properties of the joints achieved better values and a influence of the welding defects on the quality of the joints was reduced. The Laser-TIG is a good choice for welding galvanized steel sheets in the mass production of automotive industry and it could be improved by more researches.
32
Oliveira, Antonio Cesar de. "Medida de parametros biomecânicos do olho com laser de baixa coerência." Universidade de São Paulo, 1994. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-27072009-143932/.
Full textAbstract:
Neste trabalho desenvolvemos um novo método para análise biométrica do olho. Essa análise se compõe de medidas dos parâmetros biomecânicos, ou seja, espessura da córnea, distancia entre a córnea e o cristalino, espessura do cristalino, e distancia entre o cristalino e a retina. Este novo método funciona utilizando o princípio da interferometria com laser de baixa coerência. O conhecimento desses parâmetros e de suma importância para o fornecimento de dados necessários para o implante de lentes intra-oculares, em casos de catarata. Alem disso, eles permitem diagnosticar patologias clinicamente caracterizadas por suas alterações. O instrumento convencionalmente utilizado para essas medidas e o biômetro ultra-sônico. Embora esses biômetros sejam práticos e eficientes, a resolução por análise ultra-sônica esta limitada ao fato do tecido ocular não fornecer ecos satisfatórios em freqüências muito acima de 10 MHz. Uma limitação na resposta de freqüência determina uma subseqüente limitação na precisão de medida, já que esta será tanto maior quanta maior a freqüência. Uma variedade de técnicas diferentes tem sido experimentada nos últimos dez anos visando estabelecer um método mais preciso. Entretanto, várias das alternativas existentes têm sido rejeitadas devido à complexidade operacional e altos custos. A técnica interferométrica, entretanto, reúne alta resolução, simplicidade operacional e baixo custo. Isso pode ser constatado pelos resultados obtidos, os quais revela um enorme potencial aplicativo para futuros trabalhos de pesquisa ou mesmo de diagnose.In this work we have developed a new method for biometric analysis of the eye. This analysis consists of measurements of biomechanical parameters, like thickness of the cornea, distance between the cornea and the crystalline lens, thickness of the crystalline lens and distance between the crystalline lens and the retina. In this new method we use the interferometric principle with a low coherence laser. The knowledge of these parameters is very important in order to supply the necessary data for the implant of intraocular lenes, in the cases of cataract. Besides of allow the diagnosis of the pathologies, which are characterized by their changes. The instrument used in the measurements is an ultrasonic biometer. However the resolution of this instrument is limited by the ocular tissue, which does not allow satisfactory echos in frequencies above 10 MHz. A variety of the techniques have been used in the last ten years in the order to establish a more accurate method. However most of the existing alternatives have been rejected due to operational complexity and high cost. The interferometric technique unites high resolution, operational simplicity and low cost. This can be concluded by the results obtained in this work, which demonstrate the great potentiality of the method for future in academic research or clinical diagnosis.
33
Varano, Nathaniel David. "Fluid Dynamics and Surface Pressure Fluctuations of Turbulent Boundary Layers Over Sparse Roughness." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/26918.
Full textAbstract:
Turbulent boundary layers over rough surfaces are a common, yet often overlooked, problem of practical engineering importance. Development of correlations between boundary layer parameters that can be used in turbulence models and the surface geometry is the only practical option for solving these problems. Experiments have been performed on a two-dimensional zero pressure gradient turbulent boundary layer over sparsely spaced hemispherical roughness elements of 2 mm diameter. Laser Doppler velocimetry was used to measure all three components of velocity. The friction velocity was calculated using an integral momentum balance. Comparisons were made with various fitting methods that assume the von Kármán constant is appropriate for rough walls. Results indicate that this is not the case, and that the slope of the semi-logarithmic portion of the mean streamwise profile may be a function of the ratio of inner and outer length scales. Comparisons were also made between various correlations that relate the surface geometry to the behavior of the mean velocity profile. In general, the existing correlations achieved a reasonable agreement with the data within the estimated uncertainties.
A detailed study of the local turbulent structure around the roughness elements was performed. It was found that, in contrast to `sharper-edged' elements such as cylinders, an elevated region of TKE and Reynolds shear stress was found downstream of the element below the peak. This can be explained by the delay in separation of the flow coming over the top of the element due to the smooth curvature of the element.
Surface pressure fluctuation measurements were made as well using a dual microphone noise reduction technique. There have only been a few past experiments on the surface pressure fluctuations under rough wall boundary layers. However, it has been shown that the spectra of the wall fluctuations can be used to predict the far-field noise spectrum [1,2]. Therefore it is been the goal of this research to verify existing correlations between the surface pressure fluctuation spectrum and the surface geometry as well as develop new correlations that provide insight into the interactions between the turbulent motions in the flow surface pressure.Ph. D.
34
Hansen, Hanna. "Lager på lager." Thesis, Mälardalens högskola, Akademin för innovation, design och teknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-39149.
Full textAbstract:
Lager på lager är ett examensarbete i informationsdesign med inriktning rumslig gestaltning i samarbete med Västerås konstmuseum. Projektet går ut på att förtydliga och synliggöra stadens offentliga konstverk med hjälp av olika typer av tillägg eller gestaltningar. Många av stadens offentliga konstverk besitter mycket föråldrade budskap och normer som inte stämmer överens med dagens samhällsnormer och värderingar. Mitt arbete syftar till att skapa förståelse för hur ett offentligt konstverk kan bli synligt och samtidigt skapa en ifrågasättande attityd till en skulpturs grundläggande normer. Med stöd av litteratur och resultat från omvärldsanalys, rumsliganalys, formalanalys och en observation har jag tagit fram ett gestaltningsförslag som jag applicerat vid konstverket Eva som är en skulptur i Botaniska trädgården i Västerås. Eva föreställer en kvinna som med ett passivt uttryck poserar naket. Med hjälp av min gestaltning kommer Eva som konstverk och hennes inneboende normer och budskap synliggöras för att få fler människor att uppmärksamma dem. Något som förhoppningsvis både kan skapa intresse och debatt.
35
Kiani, Parnian [Verfasser], and Hartmut [Akademischer Betreuer] Schlüter. "Mass spectrometric investigation and determination of proteome composition of human skin tissues ablated using picosecond infrared laser (PIRL) in a ‘layer by layer’ approach / Parnian Kiani ; Betreuer: Hartmut Schlüter." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2019. http://d-nb.info/1186891750/34.
Full text
36
Lauer, Birthe [Verfasser], Paul [Akademischer Betreuer] Layer, and Bodo [Akademischer Betreuer] Laube. "Gene expression profiling in primary rat hepatocytes for the prediction of hepatotoxicity / Birthe Lauer. Betreuer: Paul Layer ; Bodo Laube." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2012. http://d-nb.info/1106117115/34.
Full text
37
Tree, Iho K. "Laser Doppler velocimeter measurements in a turbulent junction vortex." Diss., Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/87660.
Full textAbstract:
An experimental investigation of an incompressible, turbulent junction vortex formed at the base of a streamlined cylinder with a circular leading edge placed normal to a flat surface is documented. The flow environment is characterized by a body Reynolds number of 183,000, based on the diameter of the model. The investigation centered around measurements of mean velocity vectors at over 1,700 locations on the plane of symmetry. In addition, extensive turbulence measurements in regions of interest on the plane of symmetry were also made. All of the measurements are performed with a two-color, two-component, frequency shifted laser Doppler velocimeter.
The mean flow field shows the presence of a single vortex on the plane of symmetry and a singular separation point upstream of the vortex. From the measured data, the locations of the vortex center and the singular separation point were determined. The mean velocity field correlates well with previously published surface pressure data and surface flow visualization results.
Extensive comparisons were made with earlier Conrad and five-hole pressure probe measurements and hot film measurements. Comparisons with the Conrad probe results were made in a two-dimensional turbulent boundary layer, and with the five-hole probe results for the plane of symmetry junction vortex flow at six stations in the upstream region and four stations inside the separated region. Hot film results were compared at two stations in the upstream region. Excellent agreement was found in the two-dimensional turbulent boundary layer. On the plane of symmetry junction vortex flow, agreement among the three instruments was good, especially for data taken in the upstream region and away from the floor.
Turbulence data were also obtained with the laser Doppler velocimeter in conjunction with a minicomputer. Results indicate the turbulence level inside the separated region is significantly higher than in the upstream region. Highest levels of turbulence were found near the singular separation point and near the center of the vortex. Doppler spectra variations in these regions were also shown. In addition, Doppler histograms obtained by a PDP-11 minicomputer were compared to Doppler spectra obtained using an FFT. Excellent agreement was found between the Doppler spectra and the histograms obtained from the two different instruments.Ph. D.
38
Ciamacca, Marisa Lynn. "Foveal Phase Retardation Correlation with Henle Fiber Layer Thickness." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1492631647528424.
Full text
39
Janáková, Veronika. "Mnichovská metoda chain ladder." Master's thesis, 2011. http://www.nusl.cz/ntk/nusl-297859.
Full textAbstract:
Title: Munich chain ladder method Author: Bc. Veronika Janáková Department: Department of probability and mathematical statistic Supervisor: Mgr. Martin Pleška Supervisor's e-mail address: martin.pleska@cz.pwc.com Abstract: The insurance company is obliged to create technical reserves to cover the risk from insurance activities. One of the main reserves in non-life insurance is the IBNR reserve - the reserve to cover the damages that already exist, but that have not been reported to the insurance company yet. The content and the general aim of this thesis is to provide a better orientation in the method used in the estimation of the reserve IBNR - the Munich Chain Ladder Method. Munich Chain Ladder Method was created as a modification of the standard Chain Ladder calculation - one of the most used methods in the estimation of the IBNR reserve. The thesis focuses on the reasons that led to the modification of standard Chain Ladder calculation and explains the calculation of the modified method. It presents the application ot the method on the real data as well as the comparison with the results of the classical and less complicated Chain Ladder method. Keywords: IBNR reserve, chain ladder, Munich chain ladder 1
40
Yang, Chen-Chung, and 楊政中. "Performance analysis of Laser smoke layer dectector." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/36927375819771514809.
Full textAbstract:
碩士國立雲林科技大學
機械工程系碩士班
95
Fire damages always cast shadows on social events that people cannot forget. Besides claiming people’s lives, it’s more difficult to estimate for a great loss of treasure. According to the past statistics, the most fatal cause of building fires was dense smoke. It is because heavy smoke will bring about vision barriers, and then lead to much more difficulties in fleeing. As a result, the main purpose of this research is confer the performance test of smoke which laser smoke layer detectors bring. This research is mainly to test the voltage of smoke obscuration in different environment for judging if the external light do effect, and to change the voltage into the smoker layer obscuration ratio then estimate the eight- meter’s visibility of the emergency exit light when people are fleeing. How to use the smoke detector effectively to estimate the number of people who take refuge and flee is the main purpose of the research.
41
Hou, Shiann-chin, and 侯憲欽. "Investigation on the Recast Layer in Laser Drilling." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/34960832531608651596.
Full textAbstract:
碩士國立屏東科技大學
機械工程系
92
The purpose of this study is to discuss the influences of laser processing parameters on recast layer, when exploring laser drilling Inconel 718 material, and research for the best processing parameter combination to minimize the recast layer. Firstly, using the orthogonal array (OA) of Taguchi Method (TM) to map out the experiment layout of laser drilling parameters. The 8 selected parameters are nozzle orifice, peak power, pulse energy, assistant gas pressure, focal length, trepanning speed, focal plane position (F.P.P.), and hole diameter for the 18 experiments in the first stage. The Nd: YAG laser is used to conduct trepan drilling experiment and measure the thickness of recast layer and length of microcrack. The influences of laser drilling parameters, on the above measurements are observed, which lead to the best processing parameter combination in the first stage, by Analysis of Mean (ANOM) and Analysis of Variance (ANOVA) of Taguchi Method. In the meantime, a further analysis on the concerning processing parameters on recast layer is made for advance progress. Finally, we try to find out the connection between recast layer and microcrack. The results indicate that assistant gas pressure, peak power and focal plane position are the significant factors for the recast layer thickness. The best thickness of recast layer with processing parameter combination in the first stage is 0.045 mm, and 0.038 mm in the second stage, both of which are smaller than the 0.046 mm from the result of 18 experiments by orthogonal array; the results therefore prove the feasibility of the procedures in this research. Also found in the experiment is the corresponding length of microcrack under 0.03 mm, which does not extend into the parent material when the thickness of recast layer is under 0.05 mm, complying with the standards of aerospace parts manufacturers. The effects show that the best processing parameter combination procedures established in this study proved beneficial to processing quality of laser drilling in Inconel 718 material as well as the efficiency. Such construction can be further extended as the basis of more complete manufacturing procedures of laser processing in aerospace parts to perform as a substantial contribution to the development of aerospace industry.
42
Xu, Shao-Huang, and 徐少皇. "Laser scribing the absorption layer of CIGS solar cells." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/78677917607487321453.
Full textAbstract:
碩士國防大學中正理工學院
材料科學碩士班
99
Thin-film CIGS solar cells have the highest energy conversion efficiency among second-generation solar cells. In addition, they can be manufactured by the roll to roll process and therefore flexible modules can be fabricated. They are very promising thin film solar cells. In order to increase the output voltage of solar modules, sub-cells must be connected in series, so laser patterning processes are very important. In this study, we use three Nd:YVO4 lasers with different parameters to scribe the absorption layer of CIGS solar cells. The patterns of laser scribing were characterized using optical microscope, scanning electron microscope Alpha-Step Profilometer, and 3D surface Profilometer. The effects of laser scribing processing variables we studies by comparing the scrbe results. Finally, the processing parameters were optimized.
43
Chou, Chen-Chien, and 周辰健. "Laser-Ultrasound for the Defect Inspecting in Adhesive Layer." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/89495420176778630272.
Full textAbstract:
碩士國立中山大學
機械工程研究所
83
The Objective of this research is to develop a laserultrasound system in nondestructive applications. The surface waves were launched thermoelastically in the adhesive jointed sample using a Q-switched Nd: YAG pulsed laser to measure the bonding condition of the lap joint. In addition, the samples were also tested using surface wave launched by a PZT (piezoelectric) transducer. The experimental data from both tests were then compared to evaluate the benefits or drawbacks of using laser ultrasound. It was found that the laser induced ultrasound inspection is free of couplant, has good reproducibility, and has no transmission loss. However, the ultrasound generated by laser has low propagating energy and signal to noise ratio that increase the difficulty of measurement. In this thesis, several solutions have been proposed to overcome the above-mentioned drawbacks in this paper. Digital signal processing techniques are first used to improve the resolution of the ultrasound signal. Furthermore, the rise time of the signal is shorten by reducing the radiated area of the laser beam. Both methods are proved to be useful.
44
鄭皓文. "The study of AlN layer manufacturing by pulsed laser." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/47371483681782467048.
Full textAbstract:
碩士國立臺灣師範大學
工業教育學系
100
This study attempted to characterize the effects of the laser gas nitride parameters on the formation of aluminum nitride. By using nitrogen and ammonia as reactors and pulse Nd: YAG laser as laser medium under standard atmosphere condition without filler, the experiments were performed on the aluminum alloy 5052 with Aluminum nitride layers (AlN layers) manufacturing. We studied the surface morphology by Optical Microscope and analyzed the structure and composition by SEM、EDS and EPMA. Taguchi method was selected to set the optimized parameters of laser gas nitride. The analysis of data was carried out by ANOVA. Our results indicate that AlN layers structure from the outside to the inside are dense granularity and loosely leafy, which could reach to 14μm in thickness. The nitrogen content (N-content) of nitride layer made by ammonia is superior to those of nitrogen made. The optimized parameters obtained by Taguchi method are as following: Laser Power 40W, Pulse Width 3.7ms, Pulse Frequency 5Hz, Laser travel speed 1.5cm/min. It is shown that N-content of AlN layers relates mainly to Laser Power and Laser travel speed. Laser power has the central place in aluminum nitride formation.
45
Huang, Chien-Cheng, and 黃建程. "Machine Vision Inspection of Laser Via Copper Clay Layer." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/76051869434596335429.
Full text
46
CAI, JIA-MING, and 蔡嘉明. "0.98^^^^InGaAs/GaAs/AlGaAs strained layer single quantum well laser." Thesis, 1991. http://ndltd.ncl.edu.tw/handle/65244266414103279775.
Full text
47
Mahadevan, Pradeep. "Analysis of layer development and fusing for 3D laser printing." 2003. http://www.lib.ncsu.edu/theses/available/etd-05062003-080231/unrestricted/etd.pdf.
Full text
48
YANG, TZU-PING, and 楊子平. "Development and Research on Laser Components for Smoke Layer Measurement." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/6n7d9k.
Full text
49
魏中聖. "Numerical and Experimental Residual Stress Analysis on Laser Hardfacing Layer." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/79230260231513079005.
Full textAbstract:
博士國立中正大學
機械系
91
The hole-drilling method is applied extensively in the residual stress measurement. The integral hole-drilling method is further developed for improving the accuracy of the hole-drilling method especially for measuring residual stresses varying abruptly with depth. One of the important factors affecting the accuracy of stress values obtained from hole-drilling method is the calibration coefficients. A three-dimensional finite element model was established to determine and to improve the calibration coefficients for integral hole-drilling method. The calibration coefficients could be determined within one computation procedure with this model. The relationship between the calibration coefficients and plate thickness was investigated and the calibration coefficients determined in this work can be extended to measure residual stresses of either thin or thick plates. Experimental validation of the calibration coefficients for integral hole-drilling method based on the improved 3-D FE model was achieved using bending test of a cantilever beam. Experimental results of the bending test show a significant improvement of the accuracy of relieved stress calculation. Experimental results also show that significant error in the residual stress measurement could be induced if calibration coefficients were not chosen correctly for corresponding plate thickness. A transitional dimensionless thickness was proposed by examining the calculated relieved stresses obtained from the calibration coefficients for different plate thicknesses. The probability bounds of relieved stress corresponding to both cases were also calculated to reveal the improvement of the calibration coefficients obtained from 3-D model. Numerical simulation on the bending test was performed using a FEM model. The results show that the calculated residual stress value was strongly affected by the hole diameter used to evaluate the residual stress, and the error was attributed to the deviation of real hole geometry from an idealized model. Correction of the diameter was proposed to effectively reduce the error in the residual stress calculation. Integral hole-drilling method with improved calibration coefficients was applied to determine residual stresses at the interface of the clad layer for better accuracy. The transverse and longitudinal residual stress distributions near the interface between the clad layer and substrate is less uniform as that in the clad layer owing the phase transformation of the substrate and dissimilar properties between clad layer and substrate. The measured results at each hole depth increment revealed a good reproducibility of the integral hole-drilling method. Numerical analysis on the residual stress distribution of the laser clad layer was conducted considering the phase transformation of the substrate. A modified Goldak’s model was used to simulate the heat source and a reasonable shallow fusion zone was achieved. Thermo-metallurgical computation enables the quantitatively determination of phase proportion of the substrate after laser cladding. The resulted temperature history and the phase proportion were used to interpret the residual stress distribution obtained from integral hole-drilling method. The predicted residual stress distribution was consistent with the compared with the measured residual stresses in trends. With the help of numerical analysis, we had a better understanding on the development of the residual stresses in the laser clad layer.
50
HUANG, HSIEN-CHUNG, and 黃顯川. "Diode laser end-pumped solid-state laser studies:pump-position effect and multi-layer E-O Q-switch." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/24962935808285081595.
Full textAbstract:
博士國立中央大學
光電(科學)研究所
85
In this paper, we have studied the effect of the pumping beam focus positionon the output of an end-pumping diode laser pumped solid-state laser by calculating the changes in the overlap of the intensity distribution functionof the pump and the oscillatig beams. It is shown that the output power isstrongly pump position dependent. And, the optimized pumping position is a function of the pump beam and oscillation mode spot sizes. Our experiment results agress well with our theoretical predictions. We also propose a new type of Q-switch laser design, which is a multi-layeroptical film of electro-optical Q-switch. The major advantages of this Q-switch laser design are ultra-low operation voltage and very compact in dimension forsemiconductor laser end-pumped solid-state laser. The multi-layer optical filmeven can attached to one end of the active medium to act simultaneously as onereflector of the optical resonator. Can design an alignment free of Q-switch lase