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Phase-matching Second-order Optical Nonlinear Interactions using Bragg Reflection Waveguides: A Platform for Integrated Parametric DevicesAbolghasem, Payam 29 August 2011 (has links)
Bragg reflection waveguides (BRW) or one-dimensional photonic bandgap structures have been demonstrated for phase-matching chi(2) nonlinearities in AlxGa1-xAs. The method exploits strong modal dispersion of a Bragg mode and total internal reflection modes co-propagating inside the waveguide. It is shown that phase-matching is attained among the lowest order modes of interacting harmonics, which allows maximizing the utilization of harmonics powers for nonlinear interactions.
As our first demonstration, we report second-harmonic generation (SHG) of a 2-ps telecommunication pump in a 2.4 mm long slab BRW. The conversion efficiency is estimated as 2.0 %/W.cm^2 with a generated SH power of 729 nW. This efficiency has been considerably improved by introducing lateral confinement of optical modes in ridge structures. Characterizations denote that efficiency of SHG in ridge BRWs can increase by over an order of magnitude in comparison to that of the slab device. Also, we report continuous-wave SHG in BRWs. Using a telecommunication pump with a power of 98 mW, the continuous-wave SH power of 23 nW is measured in a 2.0 mm long device.
Significant enhancements of chi(2) interactions is obtained in the modified design of matching-layer enhanced BRW (ML-BRW). For the first time, we report type-II SHG in ML-BRW, where the second-harmonic power of 60 µW is measured for a pump power of 3.3 mW in a 2.2 mm long sample. Also, we demonstrate the existence of type-0 SHG, where both pump and SH signal have an identical TM polarization state. It is shown that the efficiency of the type-0 process is comparable to type-I and type-II processes with the phase-matching wavelengths of all three interactions lying within a spectral window as small as 17 nm. ML-BRW is further reported for sum-frequency and difference-frequency generations. For applications requiring high pump power, a generalized ML-BRW design is proposed and demonstrated. The proposed structure offsets the destructive effects of third-order nonlinearities on chi(2) processes when high power harmonics are involved. This is carried out through incorporation of larger bandgap materials by using high aluminum content AlxGa1-xAs layers without undermining the nonlinear conversion efficiency.
Theoretical investigations of BRWs as integrated sources of photon-pairs with frequency correlation properties are discussed. It is shown that the versatile dispersion properties in BRWs enables generation of telecommunication anti-correlated photon-pairs with bandwidth tunablity between 1 nm and 450 nm.
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Structural Investigation of Biological and Semiconductor Nanostructures with Nonlinear Multicontrast MicroscopyCisek, Richard 12 December 2013 (has links)
Physical and functional properties of advanced nano-composite materials and biological structures are determined by self-organized atoms and molecules into nanostructures and in turn by microscopic organization of the nanostructures into assemblies of higher structural complexity. Therefore, microscopes are indispensable tools for structural investigations at various levels of organization. In this work, novel nonlinear optical microscopy methods were developed to non-invasively study structural organization at the nanoscopic and microscopic levels. Atomic organization of semiconductor nanowires, molecular organization of amylose biocrystallites in starch granules, and microscopic organization of several photosynthetic organisms was elucidated.
The structure of ZnSe nanowires, key components in many modern nanodevices, was investigated using polarization harmonic generation microscopy. Based on nonlinear optical properties of the different crystal lattices, zinc blende and wurtzite nanowires were differentiated, and the three-dimensional orientation of the zinc blende nanowires could be found. The structure of starch granules, a model biocrystal, important in food as well as health sciences, was also investigated using polarization harmonic microscopy. The study was combined with ab initio calculations using the crystal structures of amylose A and B, revealing that second harmonic signals originate from the hydroxide and hydrogen bonds in the starch granules. Visualization of several photosynthetic organisms including the green algae, Chlamydomonas reinhardtii, two species of cyanobacteria, Leptolyngbya sp. and Anabaena sp., aggregates of light-harvesting pigment-protein complexes as well as chloroplasts from green plants were also explored, revealing that future nonlinear microscopy applications could include structural studies of cell walls, the Chlamydomonas eyespot, and photosynthetic membranes.
In this study, several nonlinear optical microscopy modalities were developed for quantitative structural investigations of nano and micro-sized architectures. Non-invasive extraction of crystallographic information in microscopic samples will have a number of potential benefits, for example, in clinical applications, allowing observations of disease states inside tissues without the need for biopsy. Industrial nanotechnology will benefit from fast determination of nanostructures with nonlinear microscopy that will improve quality of nanodevices.
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Phase-matching Second-order Optical Nonlinear Interactions using Bragg Reflection Waveguides: A Platform for Integrated Parametric DevicesAbolghasem, Payam 29 August 2011 (has links)
Bragg reflection waveguides (BRW) or one-dimensional photonic bandgap structures have been demonstrated for phase-matching chi(2) nonlinearities in AlxGa1-xAs. The method exploits strong modal dispersion of a Bragg mode and total internal reflection modes co-propagating inside the waveguide. It is shown that phase-matching is attained among the lowest order modes of interacting harmonics, which allows maximizing the utilization of harmonics powers for nonlinear interactions.
As our first demonstration, we report second-harmonic generation (SHG) of a 2-ps telecommunication pump in a 2.4 mm long slab BRW. The conversion efficiency is estimated as 2.0 %/W.cm^2 with a generated SH power of 729 nW. This efficiency has been considerably improved by introducing lateral confinement of optical modes in ridge structures. Characterizations denote that efficiency of SHG in ridge BRWs can increase by over an order of magnitude in comparison to that of the slab device. Also, we report continuous-wave SHG in BRWs. Using a telecommunication pump with a power of 98 mW, the continuous-wave SH power of 23 nW is measured in a 2.0 mm long device.
Significant enhancements of chi(2) interactions is obtained in the modified design of matching-layer enhanced BRW (ML-BRW). For the first time, we report type-II SHG in ML-BRW, where the second-harmonic power of 60 µW is measured for a pump power of 3.3 mW in a 2.2 mm long sample. Also, we demonstrate the existence of type-0 SHG, where both pump and SH signal have an identical TM polarization state. It is shown that the efficiency of the type-0 process is comparable to type-I and type-II processes with the phase-matching wavelengths of all three interactions lying within a spectral window as small as 17 nm. ML-BRW is further reported for sum-frequency and difference-frequency generations. For applications requiring high pump power, a generalized ML-BRW design is proposed and demonstrated. The proposed structure offsets the destructive effects of third-order nonlinearities on chi(2) processes when high power harmonics are involved. This is carried out through incorporation of larger bandgap materials by using high aluminum content AlxGa1-xAs layers without undermining the nonlinear conversion efficiency.
Theoretical investigations of BRWs as integrated sources of photon-pairs with frequency correlation properties are discussed. It is shown that the versatile dispersion properties in BRWs enables generation of telecommunication anti-correlated photon-pairs with bandwidth tunablity between 1 nm and 450 nm.
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Structural Investigation of Biological and Semiconductor Nanostructures with Nonlinear Multicontrast MicroscopyCisek, Richard 12 December 2013 (has links)
Physical and functional properties of advanced nano-composite materials and biological structures are determined by self-organized atoms and molecules into nanostructures and in turn by microscopic organization of the nanostructures into assemblies of higher structural complexity. Therefore, microscopes are indispensable tools for structural investigations at various levels of organization. In this work, novel nonlinear optical microscopy methods were developed to non-invasively study structural organization at the nanoscopic and microscopic levels. Atomic organization of semiconductor nanowires, molecular organization of amylose biocrystallites in starch granules, and microscopic organization of several photosynthetic organisms was elucidated.
The structure of ZnSe nanowires, key components in many modern nanodevices, was investigated using polarization harmonic generation microscopy. Based on nonlinear optical properties of the different crystal lattices, zinc blende and wurtzite nanowires were differentiated, and the three-dimensional orientation of the zinc blende nanowires could be found. The structure of starch granules, a model biocrystal, important in food as well as health sciences, was also investigated using polarization harmonic microscopy. The study was combined with ab initio calculations using the crystal structures of amylose A and B, revealing that second harmonic signals originate from the hydroxide and hydrogen bonds in the starch granules. Visualization of several photosynthetic organisms including the green algae, Chlamydomonas reinhardtii, two species of cyanobacteria, Leptolyngbya sp. and Anabaena sp., aggregates of light-harvesting pigment-protein complexes as well as chloroplasts from green plants were also explored, revealing that future nonlinear microscopy applications could include structural studies of cell walls, the Chlamydomonas eyespot, and photosynthetic membranes.
In this study, several nonlinear optical microscopy modalities were developed for quantitative structural investigations of nano and micro-sized architectures. Non-invasive extraction of crystallographic information in microscopic samples will have a number of potential benefits, for example, in clinical applications, allowing observations of disease states inside tissues without the need for biopsy. Industrial nanotechnology will benefit from fast determination of nanostructures with nonlinear microscopy that will improve quality of nanodevices.
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Metallische Nanoantennen: Frequenzverdopplung und photochemische Reaktionen auf kleinen SkalenReichenbach, Philipp 11 April 2012 (has links) (PDF)
Diese Arbeit beinhaltet experimentelle und theoretische Untersuchungen der optischen Frequenzverdopplung (second-harmonic generation, kurz SHG) an metallischen Nanopartikeln. Frequenzverdopplung bedeutet, daß ein bei der Frequenz omega angeregtes Nanopartikel Strahlung der Frequenz 2*omega emittiert. Dieser Effekt tritt nicht nur in Materialien mit nichtzentrosymmetrischer Kristallstruktur, sondern auch an der Oberfläche von Metallen auf. Deshalb läßt er sich gut mit plasmonischen Feldüberhöhungen an metallischen Nanoantennen verbinden.
Die Frequenzverdopplung wird an verschiedenen Nanostrukturen wie dreieckförmigen, stäbchenförmigen und vor allem kegelförmigen Nanopartikeln experimentell untersucht, welche aufgrund ihrer scharfen Spitzen starke SHG-Signale emittieren.
Besonders die Kegel sind interessant: Bei Anregung mit einem fokussierten, radial polarisierten Strahl dominiert je nach Kegelgröße und Umgebungsmedium ein SHG-Signal entweder von der Spitze oder von der Bodenkante des Kegels.
Diese an den Kegeln gemessenen Resultate werden durch theoretische Untersuchungen untermauert. In diesen Rechnungen werden die plasmonischen Feldüberhöhungen und die sich daraus ergebende Frequenzverdopplung für einen Kegel mit verschiedenen Parametern modelliert.
An einem einzelnen Kegel gewonnene Resultate werden auch mit den Fällen eines kugelförmigen und eines stäbchenförmigen Partikels verglichen.
Ein weiterer Gegenstand der theoretischen Untersuchungen ist die Superposition der zweiten Harmonischen von mehreren emittierenden Nanopartikeln zu einem Feldmaximum. Dabei wird eine kreisförmige Anordnung von 8 Nanostäbchen bzw. Nanokegeln von einer radial polarisierten Mode angeregt. Die Superposition der emittierten zweiten Harmonischen ergibt ein Feldmaximum innerhalb der Anordnung der Emitter. Durch eine Verkippung des anregenden Strahls kann dieser Fokus im Raum bewegt werden.
Letztere Untersuchung ist insbesondere interessant im Hinblick auf lokalisierte photochemische Reaktionen, die durch das frequenzverdoppelte Licht von Nanopartikeln ausgelöst werden sollen. Mit chemischen Substanzen, die bei omega transparent, bei 2*omega aber photoreaktiv sind, wäre im Nahfeld dieser Nanoantennen eine starke Lokalisierung der Reaktion auf Bereiche kleiner als 100~nm möglich.
Anhand von Photolacken und Polymermatrizen mit diesen Eigenschaften wird experimentell untersucht, ob frequenzverdoppeltes Licht überhaupt solche Reaktionen auslösen kann oder ob die photochemische Reaktionen überwiegend durch direkte Zwei-Photonen-Absorption des anregenden Lichts ausgelöst werden. Die Ergebnisse zeigen allerdings, daß die Zwei-Photonen-Absorption dominant ist. Durch die Zwei-Photonen-Absorption im Nahfeld von Partikeln ist aber dennoch eine vergleichbare Lokalisierung der Reaktion möglich. / This work includes experimental and theoretical investigations of second-harmonic generation (SHG) at metallic nanoparticles. SHG means that a nanoparticle that is excited at the frequency omega emits radiation at the frequency 2*omega. SHG does not only occur in materials with noncentrosymmetric structure, but also on metal surfaces. Hence, SHG can be combined well with plasmonic field enhancement at metallic nanoantennae.
SHG is investigated experimentally at different nanostructures such as triangle-like, rod-like and especially cone-like nanoparticles. With their sharp tips these structures show a much stronger SHG signal than spherical nanoparticles. Especially the cones are interesting: Excited with a focused radially polarized beam, for different cone sizes and in different surrounding media either the signal from the tip or the signal from the bottom edge dominates.
The measurement results from the cones are underpinned by theoretical investigations. In these calculations the plasmonic field enhancements and the resulting SHG are modeled for a cone with different parameters. The single-cone results are also compared with the cases of a spherical or rod-shaped particle.
A further subject of the theoretical investigations is the superposition of the SHG radiation from a number of emitting nanoparticles to a field maximum. For that, a circular arrangement of 8 nanorods or nanocones is excited by a radially polarized beam. The superposition of the second-harmonic radiation fields yields a field maximum in the space between the emitters. A tilt of the exciting beam can move this focus in space.
The latter item is of special interest concerning localised photochemical reactions induced by the second-harmonic light from nanoparticles. In the near field of these nanoantennae, a strong localisation of the reaction on regions smaller than 100 nm would be possible by using chemical substances being transparent at omega, but photoreactive at 2*omega.
With photoresists and polymer matrices, experiments are carried out to investigate whether SHG light can trigger such reactions at all, or if these photochemical reactions are triggered predominantly by direct two-photon absorption of the exciting light. The results show that the two-photon absorption is the dominant process. Yet, through two-photon absorption in the near field of particles, the localisation of the reaction is still similar.
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Das unstetige Galerkin-Verfahren in der NanooptikHille, Andreas 08 March 2013 (has links) (PDF)
Die Nanooptik beschäftigt sich mit der Wechselwirkung von Licht mit Materie, deren charakteristische Dimension im Nanometer Bereich liegt. Insbesondere wenn die Materie aus Metall besteht, zeigen sich interessante, wellenlängenabhängige Unterschiede in der Stärke der Wechselwirkung. Die Ursache dafür sind die kollektiven Moden der quasifreien Ladungsträger, die Plasmonen. Obgleich sich experimentelle Methoden in den letzten Jahren stetig verbessert haben, ist es nach wie vor nur mit erheblichem Aufwand möglich, sich Einblicke in die mikroskopischen Zusammenhänge zu verschaffen. Eine Ergänzung zu den Experimenten bieten theoretische Modelle. Auf Grund der sich mit der Zeit stetig verbesserten Leistung der Rechentechnik, kommen dabei zunehmend numerische Verfahren zum Einsatz. Eines dieser Verfahren ist das Unstetige Galerkin Verfahren, welches in dieser Arbeit auf folgende Fragestellungen der plasmonischen Nanooptik angewandt wurde:
• Bei dem unstetigen Galerkin Verfahren werden die zu simulierenden Körper üblicherweise mittels Dreiecke und Tetraeder approximiert. Da die Geometrie der metallischen Systeme einen entscheidenden Einfluss auf die Wechselwirkung hat, wurde untersucht, inwieweit sich durch Einsatz von Elementen mit gekrümmten Flächen die Genauigkeit oder die Geschwindigkeit der Simulation steigern lässt. Es konnte gezeigt werden, dass runde Elemente die Genauigkeit bei gleicher Diskretisierung um bis zu zwei Größenordnungen steigern oder die Rechenzeit bei gleicher Genauigkeit auf ein Sechstel verkürzen können.
• Bestrahlt man Metallnanopartikel mit intensiven Laserpulsen, so strahlen diese nicht nur bei der Frequenz des eingestrahlten Lichtes, sondern auch bei der doppelten Frequenz ab. Dieses Phänomen der Frequenzverdopplung (SHG, engl.: „Second-Harmonic-Generation“) ist unter anderem von der Form der Partikel und der Wellenlänge des Pulses abhängig. Da durchstimmbare gepulste Laser sehr teuer sind, wurde untersucht, ob sich mit Hilfe der linearen Partikelspektren Vorhersagen über die Stärke der Frequenzverdopplung machen lassen. Dabei wurde festgestellt, dass die Effizienz der Frequenzverdopplung zunimmt, wenn man die linearen Resonanzen der Partikel auf die SHG- oder Anregungswellenlänge abstimmt. Schafft man es, das plasmonische System so einzustellen, dass sowohl die Anregungswellenlänge, wie auch die SHG- Wellenlänge auf einer linearen Resonanz liegen, so kann die Effizienz der SHG weiter gesteigert werden. / Nanooptics is a discipline dealing with the interaction of light with matter where its characteristic dimensions are defined to be in the range of nanometers. In particular, if the matter consists of metal, i.e. conductive material, interesting wavelength dependent phenomena can be observed, which scale with the strength of the interaction. These phenomena are caused by the formation of collective modes between quasi-free charge carriers resulting in so called plasmons. Although improved experimental methods have evolved over the last few years, insight into the microscopic relationship between light and matter is only achievable with high effort. Supplemental information to experimental findings can be drawn from theoretical models. Due to the constantly improving computational power, numerical methods are progressively more employed. One of these methods is the discontinuous Galerkin method, which was applied to the following problems in plasmonic nanooptics:
• Within the discontinuous Galerkin method the simulated objects are usually approximated by triangles or tetrahedrons. Since the geometry of conductive systems has a major impact on the interaction between light and matter, the usability of elements with curved surfaces for the discretisation of the space has been investigated with respect to accuracy and speed of the simulation. In this work, it could be shown that curved elements improve the simulations precision up to two orders of magnitude with the same amount of discretisation compared to linear elements. Related to speed, it has been found that the computational time is reduced by a factor of 6 with a comparable simulation accuracy.
• By irradiating metallic nanoparticles with high power laser pulses these particles do not only emit light of the same frequency as the incident electromagnetic wave, but also with the doubled frequency (SHG, second harmonic generation). Among other things, this phenomenon of frequency doubling mainly depends on the geometry of the particle and the wavelength of the pulse. Since tunable pulsed laser sources are very expensive, it has been theoretically investigated if the strength of the frequency doubling can be deduced from the particles linear spectra. By this, it has been discovered that the efficiency of frequency doubling can be improved by adjusting the linear resonances of the particle to the SHG or excitation wavelength. The SHG efficiency can be increased even further, if the plasmonic system is tuned to a point where both the excitation and the SHG wavelength correspond to a linear resonance of the nanoparticle.
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Wavelength Conversion in Domain-disordered Quasi-phase Matching Superlattice WaveguidesWagner, Sean 31 August 2011 (has links)
This thesis examines second-order optical nonlinear wave mixing processes in domain-disordered quasi-phase matching waveguides and evaluates their potential use in compact, monolithically integrated wavelength conversion devices. The devices are based on a GaAs/AlGaAs superlattice-core waveguide structure with an improved design over previous generations. Quantum-well intermixing by ion-implantation is used to create the quasi-phase matching gratings in which the nonlinear susceptibility is periodically suppressed.
Photoluminescence experiments showed a large band gap energy blue shift around 70 nm after intermixing. Measured two-photon absorption coefficients showed a significant polarization dependence and suppression of up to 80% after intermixing. Similar polarization dependencies and suppression were observed in three-photon absorption and nonlinear refraction. Advanced modeling of second-harmonic generation showed reductions of over 50% in efficiency due to linear losses alone. Self-phase modulation was found to be the dominant parasitic nonlinear effect on the conversion efficiency, with reductions of over 60%. Simulations of group velocity mismatch showed modest reductions in efficiency of less than 10%.
Experiments on second-harmonic generation showed improvements in efficiency over previous generations due to low linear loss and improved intermixing. The improvements permitted demonstration of continuous wave second-harmonic generation for the first time in such structures with output power exceeding 1 µW. Also, Type-II phase matching was demonstrated for the first time. Saturation was observed as the power was increased, which, as predicted, was the result of self-phase modulation when using 2 ps pulses. By using 20 ps pulses instead, saturation effects were avoided. Thermo-optically induced bistability was observed in continuous wave experiments.
Difference frequency generation was demonstrated with wavelengths from the optical C-band being converted to the L- and U-bands with continuous waves. Conversion for Type-I phase matching was demonstrated over 20 nm with signal and idler wavelengths being separated by over 100 nm. Type-II phase matched conversion was also observed. Using the experimental data for analysis, self-pumped conversion devices were found to require external amplification to reach practical output powers. Threshold pump powers for optical parametric oscillators were calculated to be impractically large. Proposed improvements to the device design are predicted to allow more practical operation of integrated conversion devices based on quasi-phase matching superlattice waveguides.
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[en] GLASS AND OPTICAL FIBER ELECTROTHERMAL POLING / [pt] POLARIZAÇÃO ELETROTÉRMICA DE VIDROS E FIBRAS ÓPTICASGLADYS ADRIANA QUINTERO ROJAS 07 March 2006 (has links)
[pt] Componentes ópticos para sistemas de telecomunicações
estão em crescente
demanda. Para aumentar a eficiência destes componentes,
reduzir os custos e
permitir a integração aos sistemas atuais, tem-se
incentivado a pesquisa de novos
materiais, como, por exemplo, a sílica fundida.
Geralmente, a sílica fundida, por
ser um meio isotrópico, não exibe efeitos não lineares de
segunda ordem como o
efeito eletro-óptico, que pode ser utilizado na fabricação
de chaves e moduladores
ópticos. No entanto, pode-se induzir na sílica uma não
linearidade de segunda
ordem (c(2)) da ordem de 1 pm/V através da técnica de
polarização eletrotérmica.
Observa-se a formação de uma camada depletada de íons e um
campo elétrico
muito intenso permanentemente gravado em sílica
polarizada. A caracterização
experimental desta camada de depleção, ou seja, espessura,
perfil e magnitude do
c(2) induzido, é importante para a compreensão do processo
físico que ocorre
durante a polarização. Podem ser encontrados na literatura
resultados muito
divergentes obtidos com diferentes técnicas de
caracterização. Não se sabe se esta
divergência é devida aos diferentes métodos usados, ou a
diferentes condições de
polarização e tipos de amostras. Nesta tese, fez-se uma
comparação entre quatro
técnicas de caracterização da espessura da camada de
depleção em sílica
polarizada: ataque químico interferométrico com ácido
fluorídrico, Maker Fringe,
microscopia óptica e de força atômica, e ataque
interferométrico com medida de
segundo harmônico em tempo real. A estabilidade da não
linearidade induzida é
importante para garantir a estabilidade de chaves e
moduladores ópticos
construídos com sílica polarizada, portanto, fez-se também
um estudo de
apagamento por temperatura da não linearidade induzida em
amostras de sílica
polarizada. Foi também estudado nesta tese a influência da
superfície da amostra
antes da polarização, fator importante para a otimização
da reprodutibilidade do
processo. Para investigar a potencialidade do
desenvolvimento de um Atenuador
Óptico Variável (VOA) a fibra óptica, também foi feito um
estudo de polarização eletrotérmica em fibras ópticas.
Estudos complementares foram realizados
envolvendo a influência do campo elétrico na taxa de
ataque de ácido fluorídrico
em fibras ópticas. Fez-se também um estudo sobre redes de
Bragg gravadas em
fibras especiais. Parte desta tese foi financiada pelo
CNPq (bolsa doutorado), pelo
Convênio Ericsson/PUC-Rio - Termo Aditivo 04 e 14, ref:
PUC.04, Polarização
de fibras ópticas, e pelo Projeto GIGA - Finep - Funttel -
CPqD, Subprojeto
Atenuador Óptico Variável a Fibra Óptica. / [en] Over the past few years, there has been a growing demand
for optical
components for telecommunication systems. In order to
increase the efficiency of
these components, reduce costs and allow integration to
current systems, efforts
have been made in researching new materials, for example,
silica. Due to its
isotropic nature, silica, ordinarily, does not present
second order effects, for
example, the electro-optic effect, which can be used for
optical switching and
modulation. However, eletrothermal poling can be used to
induce in silica a
second order nonlinearity (c(2)) of the order of 1 pm/V.
It can be observed that
poled silica has an ion-depleted layer and a permanently
recorded electric field.
The experimental characterization of this depletion layer,
i.e. width, profile and
magnitude of the induced c(2), is important for the
comprehension of the physical
process occurring during polarization. Different results
obtained with different
characterization techniques can be found in literature. It
is not known whether
diverging results in literature are due to different
methods of examination or due
to different poling conditions and sample type. This
thesis compares the findings
of four experimental techniques used to monitor the width
of the depletion region
in fused silica samples poled under similar conditions -
hydrofluoric acid (HF)
etching, Maker Fringe, optical and atomic force
microscope, and hydrofluoric acid
(HF) etching with real time monitoring of the SH signal.
The stability of the
induced nonlinearity is important to guarantee the
stability of optical switches and
modulators built with poled silica; therefore, thermal
annealing of the induced
nonlinearity in poled silica is also investigated in this
thesis. The influence of the
sample surface before poling, an important factor in
reproducibility, is also
investigated in this thesis. In order to investigate the
possibility of developing an
optical fiber Variable Optical Attenuator (VOA), optical
fiber electrothermal
poling was also investigated. Additionally, studies of the
influence of the electric
field strength on HF etching rate were made, as well as
recording of Bragg gratings on special fibers. This thesis
has been partially funded by CNPq
(Doctorate scholarship), by Ericsson/PUC-Rio Accord -
Additive term 04 e 14,
ref: PUC.04, Poling of Optical Fiber, and by GIGA - Finep -
Funttel - CPqD
Project, Variable Optical Attenuator Subproject.
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Processo alternativo de polarização termo-elétrica de indução e caracterização de não-linearidade de segunda ordem em vidros soda-lime / Alternative thermal-electric polarzation process to induce and characterize second order nonlinearity in soda-lime glasses.Moura, André de Lima 10 February 2009 (has links)
Amorphous materials present macroscopic inversion symmetry. As a consequence, their even
order nonlinearities are null. The technological interest in vitreous medium with second order
nonlinearity ( χ(2) ) to make photonic devices has stimulated the development of techniques to
induce this property. Among them, the thermal-electric field poling is one of the most
investigated due its experimental simplicity and results reproducibility.
In this work the investigations were directed to the thermal-electric field poling dynamics in
soda-lime glasses in view of identify the mainly contributions to the induced nonlinearity
stability. Initially were identified the mainly contributions to the induced electrical current. It was
observed during the polarizations electroluminescence emission which was shown to be due to
ionic displacement and air ionization outside the sample. By using a simplified ionic conduction
model was determined two activation energies: ~0,60 and ~3,8eV. The first one, determined from
the induced electrical current, was attributed to the sodium conduction; while the second ones,
determined by the electroluminescence, attributed to the calcium displacement. Besides the small
contribution to the electrical current, the calcium ions, due their small diffusion coefficient, were
identified as responsible to the possibility of induce stable second order nonlinearity in soda-lime
glasses. Based on these evidences it was used an alternative procedure in which the electrical
current flux is controlled. This procedure enabled induce stable χ(2) . This effect was
demonstrated to exist 12 months after the polarization procedure, even with a ~50% decrease.
The second harmonic generation efficiency was increased in until three times by pumping
continuously the polarized samples with infrared radiation from an Nd-YAG laser operating at
QSML regime. The threshold applied voltage to observe χ(2) was determined through a
modulated applied voltage procedure to be due to the mobility difference between sodium and
calcium. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Materiais amorfos apresentam simetria de inversão macroscópica e, como conseqüência, as nãolinearidades
ópticas de ordem par são nulas. A necessidade tecnológica de que meios vítreos
apresentem não-linearidade de segunda ordem ( χ(2) ), visando principalmente o desenvolvimento
de dispositivos fotônicos, fortalece a busca por técnicas para a sua indução. Dentre estas, o
processo termo-elétrico de polarização tem sido muito investigado devido, principalmente a sua
simplicidade experimental e a reprodutibilidade dos resultados.
Neste trabalho as investigações são dedicadas à dinâmica do processo termo-elétrico em vidros
soda-lime visando identificar as principais contribuições para a estabilidade da não-linearidade
induzida. Inicialmente foram verificadas as principais contribuições à corrente elétrica induzida.
Durante as polarizações observou-se emissão de eletroluminescência. Mostrou-se que esta é
devido ao deslocamento dos íons de cálcio e possíveis ionizações do ar fora da amostra. Usando
um modelo simplificado de condução iônica determinou-se duas energias de ativação: ~0,60 e
~3,8eV. A primeira, determinada a partir da corrente elétrica induzida, foi atribuída à condução
dos íons de sódio; enquanto a segunda, determinada pela eletroluminescência, aos íons de cálcio.
Apesar de pequena contribuição na corrente elétrica induzida, os íons de cálcio, devido ao baixo
coeficiente de difusão, foram identificados como os responsáveis pela possibilidade de indução
de χ(2) estável em vidros soda-lime. Baseado nessas evidências foi utilizado um procedimento
alternativo de polarização controlando do fluxo de corrente induzida que permitiu a indução de
χ(2) estável. Este efeito pôde ser comprovado existir 12 meses após o processo de polarização,
mesmo com redução de ~50% do valor inicial. Observou-se que a eficiência na geração de
segundo harmônico pôde ser aumentada em até 3 vezes quando as amostras polarizadas foram
bombeadas continuamente com laser Nd-YAG operando no regime QSML. Através de
procedimento com tensão elétrica aplicada modulada foi identificada a origem da tensão elétrica
de limiar como sendo devido à diferença de mobilidade entre os íons de sódio e cálcio.
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Avaliação da cicatrização da pele de rato wistar após múltiplas sessões de terapia fotodinâmicaAngarita, Dora Patricia Ramírez 25 October 2012 (has links)
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Previous issue date: 2012-10-25 / Financiadora de Estudos e Projetos / Nonmelanoma skin cancer is the most frequent disease in the world population and it is becoming a public health problem. Due to this fact, new technologies are being tested for the treatment of this disease. Photodynamic Therapy (PDT) is a noninvasive technique with an excellent cosmetic outcome, well tolerated by patients and with good healing results when used for the initial stages of cancer lesions. PDT uses molecular oxygen, light at appropriate wavelengths and the drug photosensitizers to generation of reactive oxygen species such as singlet oxygen responsible for the photoinactivation of target cells. The characteristics of scar tissue after multiple sessions of PDT is not completely understood. It is not known whether multiple sessions of PDT may cause irreversible changes in the treated tissue. Thus, the present study has as its main objective the evaluation of the characteristics of the skin scarred after multiple sessions of PDT. For this study, we used 25 Wistar type male mice. These 25 mice were grouped into 5 subgroups of 5 each: G0, control group, non-subjected to any treatment; G1, exposed to one PDT session and after, there was made a lesion with CO2 laser over the scarred tissue; G2, the group is submitted twice for the same procedure, G3, subjected to 3 times the procedure performed for G1 group; G4, exposed to 4 times the procedure. Once the mice s skin was healed, we performed macroscopic and microscopic evaluations of the histological pieces. Furthermore, we made a microscopic evaluation of collagen fibers and the generation of the second-harmonic through multiphotons microscopy. Macroscopically, it was observed a good healing for the different groups. The aesthetic result showed a decrease after the third and fourth sessions. In the microscopic study, it was observed an conservation of the quantity of sebaceous glands per square millimeter (mm2). The morphology of collagen fibers when evaluated using two-photon excited fluorescence in the confocal microscope, showed thinner fibers with a parallel arrangement and lower density in the G3 e G4 compared to the control group. It was not observed decrease in the generation of second harmonic in histopathology slides. These results suggest that healing in skin after four (4) sessions of PDT/lesion presents alterations in aesthetic and histological of the morphology of collagen fibers that may be related to submitted of the skin in eight (8) consecutive occasions with an incomplete healing between them. / O Câncer de pele não melanoma é o câncer mais frequente da população mundial, se tornando um problema de saúde pública. Devido a essa problemática, novas tecnologias estão sendo testadas para o tratamento desta doença. A Terapia Fotodinâmica (TFD) é uma técnica não invasiva com excelentes resultados estéticos, bem tolerada pelos pacientes e com bons resultados de cura quanto usado para lesões iniciais. Usa o oxigênio molecular, a luz num comprimento de onda adequado e o medicamento fotossensibilizador para formar espécies altamente reativas como o oxigênio singleto responsável pela fotoinativação das células alvo. As características do tecido cicatrizado após múltiplas sessões de TFD não são completamente conhecidas. Ainda não se tem conhecimento se múltiplas sessões de TFD podem ocasionar modificações irreversíveis no tecido tratado. Desta forma, o presente estudo tem como principal objetivo a avaliação das características da pele cicatrizada após múltiplas sessões de TFD. Para este estudo, aprovado pelo comitê de ética e pesquisa foram utilizados 25 ratos machos, da linhagem Wistar, divididos em 5 grupos com 5 animais por cada grupo: G0 controle, não foi submetido a nenhum procedimento; G1, submetidos a uma sessão de TFD na pele do dorso, posteriormente, nesta pele cicatrizada foi feita uma lesão externa com laser de CO2; G2, o grupo passa duas vezes pelo mesmo procedimento explicado anteriormente; G3, o grupo passa três vezes pelo procedimento e para o grupo G4 é repetido os procedimentos em quatro ocasiões. Após a cicatrização dos procedimentos é feita uma avaliação macroscópica, um analise microscópica e uma avaliação da microestrutura das fibras de colágeno e geração do segundo harmônico por microscopia multi-fótons. Macroscopicamente, foi observada uma cicatrização satisfatória para os diferentes grupos tratados se apresentando uma diminuição no resultado estético após a terceira e a quarta sessão. No estudo microscópio, foi evidente uma conservação da quantidade de glândulas sebáceas por mm2. A morfologia das fibras de colágeno apresentaram modificações que foram mais acentuadas na terceira e quarta sessão, se evidenciando fibras de menor espessura, com uma disposição paralela e menor densidade quando comparadas ao grupo controle. Não foi evidente diminuição da geração do secundo harmônico nas lâminas estudadas. A partir destes dados sugere-se que a cicatrização na pele após 4 sessões de TFD/lesão, apresenta modificações no resultado estético, histológico, da morfologia das fibras de colágeno que podem estar relacionadas com acometimento consecutivo da pele em 8 ocasiões com uma cicatrização incompleta entre elas.
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