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TOWARDS DIRECT WRITING OF 3-D PHOTONIC CIRCUITS USING ULTRAFAST LASERS
Title
TOWARDS DIRECT WRITING OF 3-D PHOTONIC CIRCUITS USING ULTRAFAST LASERS.
Creator
Zoubir, Arnaud, Richardson, Martin, University of Central Florida
Abstract / Description
The advent of ultrafast lasers has enabled micromachining schemes that cannot be achieved by other current techniques. Laser direct writing has emerged as one of the possible routes for fabrication of optical waveguides in transparent materials. In this thesis, the advantages and limitations of this technique are explored. Two extended-cavity ultrafast lasers were built and characterized as the laser sources for this study, with improved performance over existing systems. Waveguides are...
Show moreThe advent of ultrafast lasers has enabled micromachining schemes that cannot be achieved by other current techniques. Laser direct writing has emerged as one of the possible routes for fabrication of optical waveguides in transparent materials. In this thesis, the advantages and limitations of this technique are explored. Two extended-cavity ultrafast lasers were built and characterized as the laser sources for this study, with improved performance over existing systems. Waveguides are fabricated in oxide glass, chalcogenide glass, and polymers, these being the three major classes of materials for the telecommunication industry. Standard waveguide metrology is performed on the fabricated waveguides, including refractive index profiling and mode analysis. Furthermore, a finite-difference beam propagation method for wave propagation in 3D-waveguides is proposed. The photo-structural modifications underlying the changes in the material optical properties after exposure are investigated. The highly nonlinear processes of the light/matter interaction during the writing process are described using a free electron model. UV/visible absorption spectroscopy, photoluminescence spectroscopy and Raman spectroscopy are used to assess the changes occurring at the atomic level. Finally, the impact of laser direct writing on nonlinear waveguide applications is discussed.
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Date Issued
2004
Identifier
CFE0000236, ucf:46252
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000236
CHARACTERIZATION OF DISPERSION AND RESIDUAL STRESS IN NANOPARTICLE REINFORCED HYBRID CARBON FIBER COMPOSITES
Title
CHARACTERIZATION OF DISPERSION AND RESIDUAL STRESS IN NANOPARTICLE REINFORCED HYBRID CARBON FIBER COMPOSITES.
Creator
Selimov, Alex, Raghavan,Seetha, University of Central Florida
Abstract / Description
Hybrid carbon fiber reinforced composites are a new breed of materials that are currently being explored and characterized for next generation aerospace applications. Through the introduction of secondary reinforcements, such as alumina nanoparticles, hybrid properties including improved mechanical properties and stress sensing capabilities can be achieved. In order to maximize these properties, it is necessary to achieve a homogeneous dispersion of particulate filler. Utilizing the...
Show moreHybrid carbon fiber reinforced composites are a new breed of materials that are currently being explored and characterized for next generation aerospace applications. Through the introduction of secondary reinforcements, such as alumina nanoparticles, hybrid properties including improved mechanical properties and stress sensing capabilities can be achieved. In order to maximize these properties, it is necessary to achieve a homogeneous dispersion of particulate filler. Utilizing the photoluminescent properties of alumina, it is possible to compare local levels of particle concentration through emission intensities as a way to determine the effectiveness of the tested manufacturing parameters in increasing material homogeneity. Parameters of these photoluminescence emissions have been established to be stress dependent, which allows for in situ residual stress measurements. It is shown here that the application of silane coupling agents as particle surface treatments improves particle dispersion when compared to untreated samples. Reactive silane coupling agent (RSCA) treatments were found to provide for greater dispersion improvements when compared to non-reactive silane coupling agents (NRSCA). Higher resolution investigations into these samples found that treatment with a reactive coupling agent altered the stress state of particles concentrated around the fiber from a tensile stress state to a compressive stress state. This is proposed to result from bonding of the reactive groups on the coupling agent to the organic groups on the carbon fibers which adjusts the stress state of the particle. Future mechanical tests will verify the effects of the particle surface functionalization treatments on mechanical properties of the composites.
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Date Issued
2016
Identifier
CFH0000233, ucf:44669
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFH0000233
Analysis of residual stress and damage mechanisms of thermal barrier coatings deposited via PS-PVD and EB-PVD
Title
Analysis of residual stress and damage mechanisms of thermal barrier coatings deposited via PS-PVD and EB-PVD.
Creator
Rossmann, Linda, Raghavan, Seetha, Sohn, Yongho, Vaidyanathan, Raj, Ghosh, Ranajay, University of Central Florida
Abstract / Description
Thermal barrier coatings (TBCs) are critical to gas turbine engines, as they protect the components in the hot section from the extreme temperatures of operation. The current industry standard method of applying TBCs for turbine blades in jet engines is electron-beam physical vapor deposition (EB-PVD), which results in a columnar structure that is valued for its high degree of strain tolerance. An emerging deposition method is plasma-spray physical vapor deposition (PS-PVD), capable of...
Show moreThermal barrier coatings (TBCs) are critical to gas turbine engines, as they protect the components in the hot section from the extreme temperatures of operation. The current industry standard method of applying TBCs for turbine blades in jet engines is electron-beam physical vapor deposition (EB-PVD), which results in a columnar structure that is valued for its high degree of strain tolerance. An emerging deposition method is plasma-spray physical vapor deposition (PS-PVD), capable of producing a variety of customizable microstructures as well as non-line-of-sight deposition, which allows more complex geometries to be coated, or even multiple parts at once. The pseudo-columnar microstructure that can be produced with PS-PVD is a possible alternative to EB-PVD. However, before PS-PVD can be used to its full potential, its mechanical properties and behavior must be understood. This work contributes to this understanding by characterizing PS-PVD TBCs that have been thermally cycled to simulate multiple lifetimes (0, 300, and 600 thermal cycles). Residual stress in the thermally grown oxide (TGO) layer is characterized by photoluminescence piezospectroscopy as TGO residual stress is correlated with the lifetime of the coating. Residual stress in the top coat is characterized by Raman spectroscopy, because this stress drives cracking in the top coat that can lead to failure. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) are performed to observe microstructural and phase evolution to provide context and possible explanations for the stress results. In addition, EB-PVD samples of the same thermal cycling history are characterized in the same way so that PS-PVD can be benchmarked against the industry standard. The compressive residual stress in the TGO in both coatings was relieved with thermal cycling due to the TGO lengthening as well as microcracking. The PS-PVD samples had slightly lower TGO stress than the EB-PVD, which is attributed to the greater extent of cracking within the TGO, whereas cracking in the EB-PVD samples was at the TGO/topcoat interface. The PS-PVD cycled samples had significant cracking within the topcoat near the TGO due to both greater porosity than EB-PVD samples and regions of unmelted particles that provide little resistance to cracking. The greater convolution of the TGO in the PS-PVD samples results in greater out-of-plane tensile stresses that cause crack initiation, as well as diverts cracks away from the difficult-to-follow interface. The TGO stress results agree with existing literature and extend the thermal cycling beyond what has previously been reported for PS-PVD coatings, revealing a trend of stress relief and stress values similar to that of EB-PVD coatings in this study and in the literature. Residual stress in the topcoat for both coating types became increasingly compressive with thermal cycling, indicating loss of strain tolerance by sintering. The trend of the YSZ stress for both coating types to become more compressive with cycling and with depth agrees with the literature, and the thermal cycling is longer than has been previously reported for PS-PVD. The two coating types had quite different microstructures and crack modes as well as different as-deposited residual stresses, but after thermal cycling had similar stresses in both the TGO and top coat. No samples experienced spallation. These results indicate that, while PS-PVD coatings have different properties and behavior from EB-PVD coatings, they had comparable levels of damage to EB-PVD coatings of the same lifetime and are a viable alternative to EB-PVD. Further tuning of the processing parameters may result in PS-PVD coatings with even more similar behavior to EB-PVD coatings.
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Date Issued
2019
Identifier
CFE0007717, ucf:52429
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007717