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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
51

Filamentos em lasers de semicondutor

Nunes, Frederico Dias 15 July 1974 (has links)
Orientador: Jose Ellis Ripper Filho / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-16T21:23:58Z (GMT). No. of bitstreams: 1 Nunes_FredericoDias_M.pdf: 1344893 bytes, checksum: ca80787364a932c1ac2d146fa070387f (MD5) Previous issue date: 1974 / Resumo: Não informado / Abstract: Not informed. / Mestrado / Física / Mestre em Física
52

Estudo das ondas guiadas em lasers de semicondutor

Pudenzi, Márcio Alberto Araujo, 1952- 23 July 1980 (has links)
Orientador: Marcio D'Olne Campos / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-16T22:31:12Z (GMT). No. of bitstreams: 1 Pudenzi_MarcioAlbertoAraujo_D.pdf: 1661660 bytes, checksum: c3af5651b6917be3bcceed6e06b78fa2 (MD5) Previous issue date: 1980 / Resumo: Neste trabalho estudamos as ondas guiadas em lasers de semicondutor. Na primeira parte realizamos o estudo experimental de lasers com faixa de contato Inclinada em relação aos seus espelhos. Na segunda parte, desenvolvemos um método matricial para estudarmos a propagação e reflexão de ondas guiadas em lasers / Abstract: In this work we studied the guided waves in semiconductor lasers. In the first part we carried on the experimental measurements on lasers with stripe nonorthogonal to the mirrors. In the second part we developed a matrix method for the study of propagation and reflection of guided waves in lasers / Doutorado / Física / Doutor em Ciências
53

Chaves elétricas a semicondutor controladas por pulsos laser de picosegundos

Portella, Marcia Tereza 27 September 1984 (has links)
Orientadores: Marco Antonio Fiori Scarparo, Carlos Henrique de Brito Cruz / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-16T21:42:33Z (GMT). No. of bitstreams: 1 Portella_MarciaTereza_M.pdf: 2345427 bytes, checksum: 923e84aab02228356b3f613f56dfd5e9 (MD5) Previous issue date: 1984 / Resumo: Este trabalho teve como objetivo a construção e estudo de chaves elétricas ultra rápidas. Tais dispositivos construídos a partir de semicondutores de alta resistividade, realizam uma transformação direta da energia do pulso de luz ultra curto em sinais elétricos. Estes sinais tem tempos de subida e duração de picosegundos. Os parâmetros relevantes a construção como: geometria da linha de transmissão, contatos entre metal e semicondutor, cabos coaxiais, conexões entre cabos e linhas foram estudados. Grande atenção foi dispensada aos efeitos da potência média do laser incidente e de campos elétricos aplicados. Os materiais utilizados foram arsenieto de gálio e fosfeto de índio com diferentes distâncias entre os eletrodos. Pulsos elétricos com amplitude de 2,8 V e tempo de subida £ 50ps foram obtidos com chaves de InP a urna repetição 150 MHz / Abstract: In this work we have studied the construction of ultra-fast electrical switches activated by ultrashort laser pulses. Such devices, built based on high-resistivity semiconductors, transform the energy of ultra short light pulses in electrical signals. These signals have rise time and pulse width of the order of pico-seconds. Parameters concerning the construction as: transmission lines, metal ¿ semiconductor contacts, coaxial cables, cables and line connections have been studied. Effects of mean power of the incident laser beam and applied electrical fields have also been considered. The materials used were gallium-arsenide and indium phosphide with different distance between the electrodes. Electrical pulses with amplitudes of 2,8 V and rise times £ 50ps were obtained with switches of InP at a repetition rate of 150 MHz / Mestrado / Física / Mestre em Física
54

Fabricação e caracterização de lasers semicondutores de In 1-x GaxAsyP1-Y- 1,3 um

Prince, Francisco Carlos de, 1954- 23 July 1981 (has links)
Orientador: Navin B. Patel / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-16T22:32:45Z (GMT). No. of bitstreams: 1 Prince_FranciscoCarlosde_D.pdf: 2870915 bytes, checksum: 6d002fea748f357cbe85332e671432fa (MD5) Previous issue date: 1981 / Resumo: A idéia de se fabricar lasers semicondutores de InGaAsP surgiu em fins de 76 quando o Prof. Navin Patel retornou de uma conferência nos Estados Unidos, na qual J. Hsieh havia apresentado um trabalho sobre tais lasers. Isso encaixou muito bem nos objetivos do grupo na época, que estava se voltando para a fabricação de lasers semicondutores de GaAlAs aplicáveis em comunicações ópticas, através do projeto Laser-Telebrás. Além de alguns trabalhos publicados em revistas internacionais, este é o principal fruto do trabalho iniciado na época. O trabalho, contém duas idéias novas. Primeiro, um laser especial que evita distorções e não-linearidades na curva de intensidade de luz como função da corrente foi fabricado e caracterizado. Segundo, uma inovação nos lasers convencionais foi feita com êxito: a introdução de camadas confinantes quaternárias cuja morfologia de superfície é melhor, possibilitando uniformizar as propriedades dos dispositivos de uma determinada pastilha, e aumentar a repetibilidade do processo de fabricação. Além dessas duas idéias, a tese contém toda tecnologia desenvolvida na fabricação, desde o crescimento epitaxial até a caracterização do dispositivo final, dos lasers semicondutores de InGaAsP, incluindo propriedades ópticas, elétricas e térmicas, além de física de funcionamento de tais dispositivos / Abstract: The possibility of optical communication systems for long distance and high capacity, together with the slow degradation rate of the In1-xGaxAsyP1-y devices is the main force that drives this technology forward. To fabricate devices for such applications we need to be able produce wafers with a high device yield and low threshold current density, with a high degree of reproducibility. Optical scattering losses caused by small corrugations at the interfaces of the active layer of DH wafer, can be responsible for a considerable increase in threshold current density of a laser device, depending upon the number and nature of the corrugations present within the device. This problem of imperfect morphology at the interfaces introduces an uncontrolled variation in average threshold current density from wafer to wafer and also a large scatter in the threshold current density of devices made from a given wafer. Attempts were made to improve the binary buffer layer morphology by varying the degree of supercooling and the cooling rate. Our observations suggest that the surface morphology of the binary InP layers is influenced strongly by the substrate orientation and phosphorous losses from the substrate surface during the pre-heating period. In contrast to this, very smooth layers are obtained with the quaternary In1-xGaxAsyP1-y alloy, even when x and y as 0.03 and 0.08 respectively. The results obtained with laser devices fabricated from wafers with quaternary confining layers are very encouraging: the devices have low threshold current density, as low as 1 kA/cm2, and the threshold scatter around the average value is very small. Continuous wave operation at room temperature has been achieved for lasers with SiO2 stripe as narrow as 10mm and active layer thickness of 0.1mm. To solve the problem of nonlinearity, a special laser structure was fabricated using two-step liquid phase epitaxy. The fabrication and properties of the conventional SiO2 striped lasers and this new laser structure, are described in detail / Doutorado / Física / Doutor em Ciências
55

Modelo teorico de laser DH de GaAs incluindo calculo auto-consistente de perfil de temperatura

Mattos, Theresinha de Jesus Serra de, 1947- 23 July 1980 (has links)
Orientador: Navin B. Patel / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-17T21:15:44Z (GMT). No. of bitstreams: 1 Mattos_TheresinhadeJesusSerrade_D.pdf: 2251899 bytes, checksum: 22831eec0ff6ea63fbb8c0a6dc6e7406 (MD5) Previous issue date: 1980 / Resumo: Neste trabalho, faz-se um estudo de distribuições de temperatura, portadores, densidade de corrente e ganho, na região ativa, para um laser de heteroestrutura dupla de GaAs - AlxGa1-xAs, de faixa plana. Um método de cálculo auto-consistente é utilizado na determinação das distribuições acima mencionadas. A operação do dispositivo por injeção de corrente resulta num acréscimo de temperatura da região ativa, o que por sua vez determina novas distribuições de corrente, portadores e ganho. O processo iterativo de cálculo dessas distribuições termina quando se alcançam distribuições estacionárias. Faz-se também, um estudo da variação do índice de refração do material da região ativa, que constitue a cavidade ressonante, bem como da distribuição espacial do modo fundamental da radiação eletromagnética na cavidade, como função da distribuição final de portadores na junção em operação. O comportamento dessas distribuições no laser em operação define a corrente limiar do mesmo. A dependência da corrente limiar com a largura da faixa, espessura da camada ativa e coeficiente de difusão é também estudada. Como resultado desses cálculos, determina-se a resistência térmica do laser e estuda-se sua dependência comos vários parâmetros que caracterizam o dispositivo. Na parte experimental mede-se a variação de temperatura média da junção observando-se o espectro de emissão do dispositivo e o comportamento dos modos longitudinais da cavidade Fabry-Perot formada pelos espelhos do laser. Determina-se, experimentalmente, a resistência térmica do dispositivo por este processo e seu valor medido é comparado com o calculado. A excelente concordância entre o valor teórico e o medido da resistência térmica é um indicativo que reforça o modelo de cálculo assumido inicialmente. A variação da constante dielétrica com a temperatura é determinada medindo-se a variação térmica do comprimento de onda de um modo longitudinal em função da corrente de injeção / Abstract: In this work the temperature, carrier density, current density and gain profiles along the active region of a double-heterostructure GaAs - AlxGa1-xAs semiconductor laser have been investigated by a self-consistent iteractive rnethod developed in order to calculate these distributions. Current injection results in a temperature rise at the active region, which, in turn, entails changes in the profiles for the current and carrier densities and for the laser gain. In our calculations the iteraction was carried on until stationary distributions were reached. The refractive index profile of the active region was determined as a function of the final temperature and carrier distributions. The spatial distribution of the electromagnetic radiation for the fundamental laser mode was calculated. The behavior of these distributions during laser operation defines the threshold current, which dependence on the acti ve layer thickness and stripe width was also determined. We also carried on an experimental determination of the thermal resistance of stripe-geometry DH lasers, by varying the current pulse rate up to cw condition and determining the change in the laser wavelength of a selected Fabry-Perot mode. The measured value of thermal resistance is in excelent agreement with its calculated value. We also determined the temperature dependence of the dielectric constant from the measured spectral thermal shift of each Fabry-Perot mode as function of driving current / Doutorado / Física / Doutor em Ciências
56

Compact diode-pumped solid-state lasers

Spiekermann, Stefan January 2004 (has links)
Compact diode-pumped solid-state lasers (DPSSL) arecontinuously replacing traditional gas lasers as well asenabling completely new technology. However, compact and costefficient designs are required to satisfy end-user demands. Theaim of this thesis was therefore to investigate novel laserdesigns for given applications considering these demands. In alarge part of the thesis work, nonlinear optics were employedto realize laser wavelengths where there was no appropriatelaser transition available. Besides other nonlinear crystals such as BBO, LBO and KTP,periodically poled KTP played an important role in this thesiswork. Its unique properties regarding up conversion processeswere exploited, thus supplying a broadened view over itspotential and limitations. This thesis places emphasis on practical concerns, mainlyrelated to real applications. It gives solutions to the beamshaping of laser diodes, covers the simulation and the designof laser dynamics as well as laser performance and describesthe sources of laser output degradation and damage mechanisms.Novel infrared lasers were designed and multiple intra-cavity,external cavity and non-resonant multi-pass frequencyconversion schemes were successfully employed and optimized.These produced red, orange, green, blue and ultraviolet outputfor various applications like spectroscopy, micro machining andwriting of fiber Bragg gratings. Keywords:diode-pumped solid-state lasers, nonlinearoptics, frequency conversion,
57

Compact diode-pumped solid-state lasers

Spiekermann, Stefan January 2004 (has links)
<p>Compact diode-pumped solid-state lasers (DPSSL) arecontinuously replacing traditional gas lasers as well asenabling completely new technology. However, compact and costefficient designs are required to satisfy end-user demands. Theaim of this thesis was therefore to investigate novel laserdesigns for given applications considering these demands. In alarge part of the thesis work, nonlinear optics were employedto realize laser wavelengths where there was no appropriatelaser transition available.</p><p>Besides other nonlinear crystals such as BBO, LBO and KTP,periodically poled KTP played an important role in this thesiswork. Its unique properties regarding up conversion processeswere exploited, thus supplying a broadened view over itspotential and limitations.</p><p>This thesis places emphasis on practical concerns, mainlyrelated to real applications. It gives solutions to the beamshaping of laser diodes, covers the simulation and the designof laser dynamics as well as laser performance and describesthe sources of laser output degradation and damage mechanisms.Novel infrared lasers were designed and multiple intra-cavity,external cavity and non-resonant multi-pass frequencyconversion schemes were successfully employed and optimized.These produced red, orange, green, blue and ultraviolet outputfor various applications like spectroscopy, micro machining andwriting of fiber Bragg gratings.</p><p><b>Keywords:</b>diode-pumped solid-state lasers, nonlinearoptics, frequency conversion,</p>
58

Multi-pulse laser holography of vibrating objects

Li, Song, 李松 January 1996 (has links)
published_or_final_version / Physics / Master / Master of Philosophy
59

Chirped Pulses in Laser Amplifiers

Gieszelmann, Edward L. 06 1900 (has links)
QC 351 A7 no. 80 / This dissertation presents a theoretical investigation into the production, evolution, and asymptotic form of chirped pulses in homogeneously and inhomogeneously broadened laser amplifiers. Amplifier equations of motion are obtained in a form appropriate for dealing with such frequency-modulated pulses. The transient response of laser amplifiers to variously chirped Gaussian input pulses is studied parametrically using numerical solutions of the amplifier equations. The chirping mechanisms of the intensity dependence (Kerr effect) and the quadratic frequency dependence of the index of refraction are discussed briefly, as are the chirps produced by them and the amplification of Gaussian pulses in their presence. The amplifier whose host exhibits these dispersive effects is treated as a sequence of pairs of slices. One of each pair amplifies and exhibits the Kerr effect; the other has an index with a quadratic frequency dependence. This slice model is used to obtain steadystate pulses in both homogeneously and inhomogeneously broadened amplifiers whose host indexes have a quadratic frequency dependence. The steady-state pulse characteristics are determined as functions of amplifier parameters and the index curvature. The principal results are as follows: The homogeneously broadened amplifier responds predominately to the temporal character of a chirped input pulse whereas the inhomogeneously broadened amplifier response depends primarily upon the pulse spectrum. Of three important concepts (area theorem, echoes, and optical nutation) used to describe unchirped pulse amplification in inhomogeneously broadened media, only photon echo is useful when pulses are more than slightly chirped. The presence of the Kerr effect can produce significant chirps on large pulses. Amplification in the presence of the Kerr effect produces pulses strikingly similar to experimental results. Quadratic frequency dependence in the index has very little influence on most pulses in short amplifiers but has a cumulative effect in long amplifiers and laser oscillators. Chirped steady-state pulses exist in both homogeneously and inhomogeneously broadened amplifiers when the host index has such frequency dependence. In the homogeneously broadened case, they exist at relative gain levels dramatically below other theoretical predictions. They occur in the inhomogeneously broadened case only for the smaller index curvatures.
60

Tratamento de psoríase ungueal com laser de corante pulsado

Peruzzo, Juliano, Garbin, Gabriela Czarnobay January 2015 (has links)
Introdução: A psoríase é uma doença inflamatória crônica com prevalência estimada em 2% da população mundial. As alterações ungueais estão presentes em cerca de 50% dos casos e chegam a acometer até 80% dos pacientes em algum momento da vida. Elas costumam ser resistentes aos tratamentos convencionais e possuir caráter recidivante. O laser de corante pulsado (LCP) tem surgido como alternativa terapêutica. Objetivos: Avaliar a eficácia do LCP na psoríase ungueal e o impacto do tratamento na qualidade de vida. Métodos: Para este estudo foram selecionados quatorze pacientes com diagnóstico de psoríase das unhas provenientes do ambulatório de Dermatologia do Hospital de Clínicas de Porto Alegre ou de clínicas privadas, tratados com aplicação do LCP com fluência de 6J/cm2 e duração de pulso de 0,45ms nas unhas acometidas em sessões mensais por três meses e uma nova visita, para seguimento, após 90 dias era realizada. A avaliação objetiva dos resultados foi realizada pelo índice de gravidade da psoríase ungueal (NAPSI) e avaliação subjetiva através de registro fotográfico das unhas acometidas na primeira e na terceira sessões e 90 dias após a última sessão. O índice de qualidade de vida para dermatologia (DLQI) foi respondido na primeira e 90 dias após a última sessão. Resultados: A mediana de melhora nas contagens do NAPSI total, do NAPSI do leito e do NAPSI da matiz ungueais foram, respectivamente, de 44,15% (P=0,002), 50% (P=0,033) e 65,1% (P=0,024). Os pacientes apresentaram também melhora significativa no DLQI após o tratamento, com mediana de 40%. Conclusões: O LCP pode ser considerado uma alternativa de tratamento para psoríase ungueal. / Introduction: Psoriasis is a chronic inflammatory disease with an estimated prevalence of 2% of the world population. The nail changes are present in about 50% of cases and affect up to 80% of patients at some point in life. Nail psoriasis is often refractory to conventional treatments. Pulsed dye laser (PDL) has emerged as an alternative therapy. Objectives: To evaluate the efficacy of PDL in nail psoriasis and the impact of treatment on quality of life. Methods: For this study, were selected eleven patients diagnosed with nail psoriasis from the Dermatology clinic of the Hospital de Clínicas de Porto Alegre or private clinics. PDL was applied in affected nails with fluency of 6J/cm2 and pulse duration of 0,45ms in monthly sessions for three months. A follow-up visit after 90 days was done. The outcome assesment was made by the Nail Psoriasis Severity Index (NAPSI) and photographic records in the basement, in the third session and in the follow-up. The Dermatology Life Quality Index (DLQI) was answered in the baseline and in the follow-up. Results: The median improvement in the scores of the overall NAPSI, nail bed NAPSI and nail matrix NAPSI were respectively 44.15% (P = 0.002), 50% (P = 0.033) and 65.1% (P = 0.024). The patients also had significant improvement in DLQI after treatment with a median of 40%. Conclusions: PDL can be considered an alternative treatment for nail psoriasis.

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