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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.
131

Estudo de anomalias na potência radiada por lasers de junção semicondutora em função da excitação

Bossi, Reusi Ines 15 July 1977 (has links)
Orientador: Marcio D'Olne Campos / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-17T04:03:38Z (GMT). No. of bitstreams: 1 Bossi_ReusiInes_M.pdf: 1547817 bytes, checksum: 3037277822b87e26258865b947cc8e79 (MD5) Previous issue date: 1977 / Resumo: Não informado / Abstract: Not informed. / Mestrado / Física / Mestre em Física
132

Estudo da influência de lasers no aprisionamento de portadores, por impurezas em semicondutores submetidos a campos magnéticos fortes

Nassar, Antonio Boulhosa 23 July 1980 (has links)
Orientador: Luiz Carlos de M. Miranda / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-17T13:07:12Z (GMT). No. of bitstreams: 1 Nassar_AntonioBoulhosa_M.pdf: 910672 bytes, checksum: b8a88c23f883b6c0294809ee178d8b08 (MD5) Previous issue date: 1980 / Resumo: Neste trabalho estudou-se a blindagem de impurezas carregadas em semicondutores, submetidos a campos magnéticos fortes uniformes e radiação laser, em baixas temperaturas, e sua influência no aprisionamento dos portadores, no limite ultra-quântico. Verificou-se que a energia de ligação reduz-se drasticamente, quando a frequência do laser situa-se próxima da frequência ciclotrônica e aumenta enormemente quando próxima da frequência de plasma / Abstract: In this work the features of the screening of na ionized impurity is presented for semiconductors in the simultaneous presence of a laser field and a strong d.c. magnetic field at very low temperatures, taking into account these effects on the carriers freezeout in the ultra-quantum regime. It has been show specially that the carriers binding energy reduces abruptly when the laser is close to the cyclotron frequency and conversely diverges when is close to the plasma frequency / Mestrado / Física / Mestre em Física
133

Influência da temperatura sobre o guia de ondas de lasers do tipo poço quântico simples de GaAs

Nunes Junior, Alcides da Silva 25 April 1989 (has links)
Orientador: Theresinha de Jesus Serra de Mattos / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-17T21:52:46Z (GMT). No. of bitstreams: 1 NunesJunior_AlcidesdaSilva_M.pdf: 1525159 bytes, checksum: 1963a882ab31da54d36a40e9a36b81db (MD5) Previous issue date: 1989 / Resumo: Utilizamos a caracterização eletro-óptica em lasers do tipo Poço Quântico Simples, com camada ativa de 150Þ e contato de faixa de 4,0 mm de largura, pudemos comprovar várias teorias publicadas alem de observar novas características como o leisamento desde dois níveis de energia diferentes sendo que para o nível mais baixo a corrente limiar é mais alta do que para o nível de energia superior. Este fato se deve às altas perdas do dispositivo. Temos também a emissão laser com longos atrasos quando se opera sob regime pulsado e a análise de emissão dentro destes pulsos nos mostra que no início do pulso, para correntes não muito altas, temos leisamento desde o segundo nível com o guiamento feito através do ganho óptico enquanto que no final do pulso, ou para correntes mais altas, ocorre o leisamento desde o primeiro nível com o guiamento devido a mudança de comportamento do índice de refração do material. Outro fato que nos chamou a atenção foi a ocorrência de pulsos de luz bastante curtos (Q ¿ Switching) no final do pulso de corrente aplicado, quando o laser tem a camada ativa menor que 100Þ e o contato de faixa mais estreito que 5,0 mm / Abstract: In this work the electro-optical characterization techniques were used in order to understand the anomalous emission behavior observed for Single Quantum Well lasers with active region thinner than 150Þ and 4.O mm stripe width. We observed lone delay time laser emission involving the first and second energy levels of the Quantum Well and an unexpected lower threshold current for the higher energy mode. This is shown to be due to the high internal device losses. We showed also, that depending on current, and in the case of normal delay time observed for the higher energy mode, the light confinement is provided by gain guiding mechanism. For the lower energy mode which shows only abnormally lone delays, the guiding mechanism is showed to be due to a thermally induced real index waveguide. Q - Switching effect was also observed for lasers with active region thinner than 100Þ and less than 5.0 mm stripe width / Mestrado / Física / Mestre em Física
134

Conception et optimisation d'un laser à fibre haute puissance (kW) intégrant un réflecteur de pompe multimode

Pelletier-Ouellet, Samantha 09 November 2022 (has links)
Dans une ère basée sur les technologies, les techniques employées pour la fabrication des pièces de tout genre, que ce soit de l'usinage de précision ou du marquage jusqu'au nettoyage et traitement de surface, font intervenir les lasers. De ce fait, l'amélioration de ces lasers demeure un sujet d'actualité dans le domaine de la recherche et du développement en milieu académique et industriel. Depuis les dernières années, l'atteinte de nouveaux seuils de puissance pour les lasers à fibre, les plus communément utilisés en industrie, est limitée par des effets non linéaires tels que la diffusion Raman, l'instabilité du mode transverse, l'autofocalisation par effet Kerr, etc. Le but de ce projet de maîtrise est de développer un composant photonique ayant le potentiel de mitiger certains de ces effets non linéaires, le réflecteur de pompe, dont la fonction est de recycler la pompe résiduelle d'un laser à fibre de haute puissance opérant en régime continu. L'ajout de ce composant aux schémas de laser à fibre permet d'en réduire la longueur de la fibre de gain, ce qui, en plus de repousser le seuil des effets non linéaires, réduit également le coût global des systèmes laser à fibre. Une adaptation rotative de la méthode d'inscription classique des réseaux de Bragg par balayage du masque au laser à impulsions femtosecondes est présentée dans ce mémoire. Un système laser tout fibre émettant à 1080 nm pompé en copropagation par six diodes multimodes à 915 nm ayant une puissance totale de 774 W a été conçu. Un simulateur résolvant par la méthode de Fourier à pas alternés les équations non linéaires de Schrödinger de la propagation du signal a été utilisé pour calculer la longueur de fibre optimale dans le schéma laser seul et celui intégrant le réflecteur de pompe. Les quatre prototypes de réflecteur de pompe testés dans le laser ont amélioré l'efficacité, la puissance maximale atteinte et ils ont diminué la valeur du seuil laser par rapport à la cavité initiale. Avec le prototype le plus prometteur, l'efficacité maximale atteinte pour une cavité de 36.1 m était de 79.0 % et la puissance maximale de 608 W, ce qui représente un gain de respectivement 2.9 % et 22 W par rapport à la cavité sans réflecteur de pompe. La cavité a été raccourcie à 18.2 m, l'efficacité et la puissance maximale atteinte étaient de 69.5 % et 534 W, ce qui correspond à un gain de 5.6 % et 43 W. Un écart de seulement 74 W est obtenu soit 12 % de diminution de puissance, pour une diminution de près de 50 % de la longueur initiale de la fibre de gain. La diminution de la longueur de fibre de gain limite grandement l'élargissement spectral observé expérimentalement, tel que prévu. Il a également été démontré qu'un réseau inscrit plus large spectralement vers les hautes longueurs d'onde réfléchissait davantage les modes d'ordres supérieurs se trouvant à de grandes ouvertures numériques. / In an era that is based on technology, the techniques that are used to manufacture parts of all kinds, whether it be precision machining, marking to cleaning and surface treatment involve lasers. There by, improvement of these lasers remains a hot topic in the academic and industrial field of research and development. For the past few years, power scaling of most commonly used in industry high power fiber lasers are limited by non linear effects such as Raman scattering, transverse mode instability, self-focusing Kerr effect, etc. This master's project aims to develop a photonic component, the pump reflector, whose function is to recycle the residual pump power of a high power fiber laser in continuous-wave operation. The addition of this component to the laser scheme makes it possible to reduce the length of the gain fiber, which, in addition to pushing back the threshold of nonlinear effet and also reduces overall costs of fiber laser systems. A rotating adaptation of the classical fiber Bragg grating writing method using femtosecond laser pulses by phase mask scanning is presented in this work. An all-fiber laser system operating at 1080 nm in co-pumped configuration using six laser diodes at 915 nm with 774 W total power was designed. A simulator using a Fourier split-step method to solve the non linear Schrödinger equations that describe signal propagation was operated to calculate the optimal gain fiber length for the laser scheme alone and the one incorporating the pump reflector. The four tested prototypes in the laser have improved the laser efficiency slope, the maximum power and decreased the threshold value compared with the first cavity. With the most promising prototype, the laser efficiency slope reached 79.0 % and a maximum power of 608 W for the 36.1 m cavity which represents a gain of 2.9 % and 22 W respectively compared with the cavity without pump reflector. The cavity length was shortened to 18.2 m, the slope efficiency and the maximum power reached 69.51 % and 534 W. The maximum gain compared to the laser system alone was 5.6 % for the slope efficiency and 43 W for the maximum power. A difference of only 74 W is obtained, i.e. a 12 % reduction in power was observed by reducing the initial length of the gain fiber by 50 %. The reduction of the gain fiber length greatly limits spectral broadening; this was observed experimentaly, as expedected. It has also been demonstrated that a spectrally broader inscribed grating towards higher wavelengths reflected higher order modes present at high numerical apertures.
135

EXTERNAL FEEDBACK OPERATION OF SEMICONDUCTOR LASERS

Kempf, Paul H. G. 08 1900 (has links)
The aim of this thesis is to contribute to the understanding of the dynamics of semiconductor lasers on a 10 to 100 ps time scale when their output is altered by external feedback. The optimization of parameters involved in optoelectronic feedback results in a reduction in the measured minimum pulse FWHM relative to previous work, and gives the conditions necessary to produce 25 ps FWHM optical pulses using this technique. To aid in the understanding of the modelocking of diode lasers, the CW spectral and threshold characteristics of a diode laser coupled to a mirror external cavity are examined. It is found that multiple reflections in the compound cavity cause an increase:). in mode linewidth with increasing bias current up to a maximum for a particular level of feedback for an external mirror coupled laser, but not for a grating coupled laser. As a result of the CW optical feedback analysis, grating feedback is utilized as a probe of the laser gain in a refinement of a previously reported technique for direct gain measurement. Also, the total loss reduction induced by external optical feedback is found to be made up of the sum of mirror loss and mode propagation loss reductions. This has significance in simulations of active modelocking and injection locking tuning characteristics carried out in this work. Simulations for active modelocking of a diode laser with low residual facet reflectivity in. an external mirror cavity account for the previously unexplained extreme sensitivity of the modelocking process to oscillator stability. Grating external cavity injection locking experiments and simulations present a new scheme for obtaining nearly transform limited optical pulses using semiconductor lasers. / Thesis / Master of Engineering (ME)
136

Absorption of laser radiation in the atmosphere /

Long, Ronald Killworth January 1963 (has links)
No description available.
137

Studies in partial coherence and nonlinear optics /

Meadors, John Gilmore January 1964 (has links)
No description available.
138

Polarization effects of lasers /

Settles, Robert Andrew January 1968 (has links)
No description available.
139

Measurement of the spatial coherence and intensity correlation functions of atmospherically distorted laser waves at 0.63 and 10.6 microns /

Monroe, Marvin Eugene January 1968 (has links)
No description available.
140

DF and HF laser spectra in the infrared /

Heath, William Bernie January 1976 (has links)
No description available.

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