<p>The goal of my Ph.D. thesis is to enhance the visualization of the peripheral retina using wide-field optical coherence tomography (OCT) in a clinical setting.</p><p>OCT has gain widespread adoption in clinical ophthalmology due to its ability to visualize the diseases of the macula and central retina in three-dimensions, however, clinical OCT has a limited field-of-view of 300. There has been increasing interest to obtain high-resolution images outside of this narrow field-of-view, because three-dimensional imaging of the peripheral retina may prove to be important in the early detection of neurodegenerative diseases, such as Alzheimer's and dementia, and the monitoring of known ocular diseases, such as diabetic retinopathy, retinal vein occlusions, and choroid masses.</p><p>Before attempting to build a wide-field OCT system, we need to better understand the peripheral optics of the human eye. Shack-Hartmann wavefront sensors are commonly used tools for measuring the optical imperfections of the eye, but their acquisition speed is limited by their underlying camera hardware. The first aim of my thesis research is to create a fast method of ocular wavefront sensing such that we can measure the wavefront aberrations at numerous points across a wide visual field. In order to address aim one, we will develop a sparse Zernike reconstruction technique (SPARZER) that will enable Shack-Hartmann wavefront sensors to use as little as 1/10th of the data that would normally be required for an accurate wavefront reading. If less data needs to be acquired, then we can increase the speed at which wavefronts can be recorded.</p><p>For my second aim, we will create a sophisticated optical model that reproduces the measured aberrations of the human eye. If we know how the average eye's optics distort light, then we can engineer ophthalmic imaging systems that preemptively cancel inherent ocular aberrations. This invention will help the retinal imaging community to design systems that are capable of acquiring high resolution images across a wide visual field. The proposed model eye is also of interest to the field of vision science as it aids in the study of how anatomy affects visual performance in the peripheral retina.</p><p>Using the optical model from aim two, we will design and reduce to practice a clinical OCT system that is capable of imaging a large (800) field-of-view with enhanced visualization of the peripheral retina. A key aspect of this third and final aim is to make the imaging system compatible with standard clinical practices. To this end, we will incorporate sensorless adaptive optics in order to correct the inter- and intra- patient variability in ophthalmic aberrations. Sensorless adaptive optics will improve both the brightness (signal) and clarity (resolution) of features in the peripheral retina without affecting the size of the imaging system.</p><p>The proposed work should not only be a noteworthy contribution to the ophthalmic and engineering communities, but it should strengthen our existing collaborations with the Duke Eye Center by advancing their capability to diagnose pathologies of the peripheral retinal.</p> / Dissertation

While dental caries represents the major chronic disease of humans, visual and tactile inspection are the methods of choice in daily dental practice. Several optical technologies have been developed in recent years for the purpose of dental examination, including near-infrared light transillumination as a promising tool for the supplementation and partial replacement of radiography. In case of occlusal alterations, the incidence of surface discolorations impedes the visual assessment, whereas tactile inspection appears to yield little diagnostic information or might be detrimental. Optical coherence tomography (OCT) facilitates depth-resolved imaging with μm resolution, utilizing near-infrared light, and has already shown its potential for various dental applications. We have recently demonstrated that depolarization imaging utilizing the degree of polarization uniformity (DOPU) extends those abilities by the detection of early carious lesions, as it provides an unambiguous demineralization contrast. Here, we show that this approach also enables the assessment of occlusal enamel lesions in the presence of stains, and compare PS-OCT cross sections with polarized light microscopy (PLM) images of thin sections. For tooth samples with discoloration or demineralization, respectively, PS-OCT and PLM results are in good agreement.

No description available.

Cross-linked films of ε-caprolactone (CL) and 1,5-dioxepan-2-one (DXO) having various mole fractions of monomers and different cross-link densities were prepared using 2,2’-bis-(-caprolactone-4-yl) propane (BCP) as cross-linking agent and Sn(Oct)2 as catalyst. Reaction parameters were examined to optimize the film-forming conditions. Networks obtained were elastomeric materials, easy to cast and remove from the mould. Effect of CL content and cross-link density on the final properties of the polymer network was evaluated. Thermal, mechanical and surface properties of the films were controlled by monomer feed composition and cross-link density. The films have potential to be used for tissue engineering applications as shown by preliminary cell growth studies. To avoid organometallic catalysts in the synthesis of poly(1,5-dioxepan-2-one) (PDXO), the enzyme-catalyzed ring-opening polymerization (ROP) of DXO was performed with lipase-CA (derived from Candida antarctica) as a biocatalyst. A linear relationship between number-average molecular weight (Mn) and monomer conversion was observed, which suggested that the product molecular weight can be controlled by the stoichiometry of the reactants. The monomer consumption followed a first-order rate law with respect to monomer and no chain termination occurred. Effect of reaction water content, enzyme concentration and polymerization temperature on monomer conversion and polymer properties was studied. An initial activation by heating the enzyme was sufficient to start the polymerization as monomer conversion occurred at room temperature afterwards. Terminal-functionalized polyesters and tri-block polyesters were synthesized by lipase-CA catalyzed ROP of DXO and CL in the presence of an appropriate alcohol as initiator. Alcohol bearing unsaturation introduced a double bond at the chain end of the polyester, which is a useful pathway to synthesize comb polymers. Dihydroxyl compounds were used as macro-initiators to form tri-block polyesters. The enzyme-catalyzed polymerization of lactones has been shown to be a useful method to synthesize metal-free polyesters. / QC 20101221

Insight Photonic Solutions Inc. has continued to develop their patented VT-DBR laser design; these wavelength tunable lasers promise marked image-quality and acquisition time improvements in SS-OCT applications. To be well suited for SS-OCT, tunable lasers must be capable of producing a highly linear wavelength sweep across a tuning range well-matched to the medium being imaged; many different tunable lasers used in SS-OCT are compared to identify the optimal solution. This work electrically and spectrally characterizes two completely new all-semiconductor VT-DBR designs to compare, as well. The Neptune VT-DBR, an O-band laser, operates around the 1310 nm range and is a robust solution for many OCT applications. The VTL-2 is the first 1060 nm VT-DBR laser to be demonstrated. It offers improved penetration through water over earlier designs which operate at longer wavelengths (e.g. - 1550 nm and 1310 nm), making it an optimal solution for the relatively deep imaging requirements of the human eye; the non-invasive nature of OCT makes it the ideal imaging technology for ophthalmology. Each laser has five semiconductor P-N junction segments that collectively enable precise akinetic wavelength-tuning (i.e. - the tuning mechanism has no moving parts). In an SS-OCT system utilizing one of these laser packages, the segments are synchronously driven with high speed current signals that achieve the desired wavelength, power, and sweep pattern of the optical output. To validate the laser’s fast tuning response time necessary for its use in SS-OCT, a circuit model of each tuning section is created; each laser section is modeled as a diode with a significant lead inductance. The dynamic resistance, effective capacitance, and lead inductance of this model are measured as a function of bias current and the response time corresponding to each bias condition is determined. Tuning maps, spectral linewidths, and side-mode suppression ratio (SMSR) measurements important to SS-OCT performance are also collected. Measured response times vary from 700 ps to 2 ns for the Neptune and 1.2 to 2.3 ns for the VTL-2. Linewidth measurements range from 9 MHz to 124 MHz for the Neptune and 300 kHz to 2 MHz for the VTL-2. SMSR measurements greater than 38 dB and 40 dB were observed for the Neptune and VTL-2, respectively. Collectively, these results implicate the VT-DBR lasers as ideal tunable sources for use in SS-OCT applications.

In this project, the performance aspects of a new early generation 1310 nm Sampled-Grating Distributed Bragg Reflector (SG-DBR) semiconductor laser are investigated. SG-DBR lasers are ideal for Source Swept Optical Coherence Tomography (SS-OCT), a Fourier-Domain based approach for OCT, necessitating a tunable wavelength source. Three internal sections control the frequency output for tuning, along with two amplifiers for amplitude control. These O-band SG-DBR devices are now being produced in research quantities. SG-DBR lasers have been produced at 1550 and 1600 nm for some times. Fundamental questions regarding the performance of the 1310 nm devices must be quantified. Standard metrics including the laser linewidth, amplitude modulation and frequency modulation responses are characterized. The intrinsic electrical parasitics of the laser diode segments and packaging are also investigated. In addition, testing fixture including a Thermal Electric Cooler (TEC) controller is for the characterization task. Measurements of these key metrics are essential to the enhancement of future devices, aiding in the optimization of more mature products.

Mit der steigenden Nachfrage an elektrisch betriebenen Fahrzeugen nimmt die Batteriemodulproduktion einen immer zentraleren Stellenwert für die Automobilhersteller ein. Bei dieser wird eine Vielzahl an Batteriezellen miteinander kontaktiert. Dabei werden die Ableiter der Batteriezellen, die aus den Werkstoffen Kupfer beziehungsweise Aluminium bestehen, durch einen Laserschweißprozess stoffschlüssig miteinander gefügt. Mit der Vielzahl an zu kontaktierenden Batteriezellen geht eine ebenso große Vielzahl an Laserschweißprozessen einher. Die Taktzeit eines einzelnen Schweißprozesses liegt dabei unter 60 ms. Aus diesen Randbedingungen resultiert die Notwendigkeit eines Inline-Qualitätssicherungssystems (QS-System). Ein OCT-System, das auf einem optischen Kohärenztomographen beruht, könnte das Potential haben, die Anforderungen an ein Inline-QS-System zu erfüllen. Das OCT-System ermöglicht es, inline die Dampfkapillartiefe des Schweißprozesses beim Kontaktieren zu messen, was ein Novum darstellt. Im Rahmen dieser Arbeit wird untersucht, ob sich ein OCT-System als QS-System für die Laserschweißverbindung von Kupfer und Aluminium bei Kontaktierprozessen eignet. Dabei wird ein Scanner-basiertes OCT-System eingesetzt, das es erlaubt, den OCT-Messstrahl lokal um den Bearbeitungslaserstrahl herum autark zu positionieren. Dies ermöglicht es, an verschiedenen Stellen, bezogen auf die Position des Bearbeitungslasers, topologische, dimensionale Messungen vorzunehmen. Es kann sowohl an einer festgelegten Position innerhalb der Dampfkapillare als auch auf einer theoretischen Scanlinie gemessen werden. Dabei werden die Messungen stets auf die Bauteiloberfläche referenziert. Dies ist sowohl hinsichtlich der Genauigkeit als auch hinsichtlich der Anzahl der Referenzierungen weiterentwickelt und optimiert worden. Das OCT-System wurde ebenfalls dazu genutzt, eine Bauteillageerkennung vorzunehmen. Damit kann der Laserschweißprozess bauteiltoleranzunabhängig sowohl lateral als auch in Bezug auf die Fokuslage optimal positioniert werden. Außerdem wurde die grundsätzliche Messsystemfähigkeit sowie die Einsatzgrenzen des OCT-Systems zur Kapillartiefenmessung geprüft. Durch Linienscans des OCT-Systems und unter Zuhilfenahme von Hochgeschwindigkeitskameraaufnahmen erstellte topologische Dampfkapillarmodelle, bilden die Grundlage für die Erarbeitung von Strategien zur Qualitätsbewertung durch das OCT-System. Ein besonderes Augenmerk lag auf der Auswirkung eines Fügespaltes auf die Schweißqualität sowie die OCT-Messungen. Es wurde eine Methodik für den Fall ohne auftretenden Fügespalt erarbeitet und exemplarisch durchgeführt, mit der durch die Kapillartiefenmessungen des OCT-Systems die Einschweißtiefe berechnet werden kann. Ebenfalls wurde untersucht, ob und wie sich die Anbindebreite mit dem OCT-System bestimmen lässt. Außerdem ist ein vielversprechender Ansatz zur Bestimmung der Schweißqualität bei auftretendem Fügespalt dargestellt. Dazu wurde, basierend auf dem erarbeiteten topologischen Dampfkapillarmodell, drei Kennwerte zur Bewertung der Prozessqualität aus den Messdaten extrahiert und überwacht.:Verzeichnis der Abkürzungen und Formelzeichen Kurzfassung Abstract 1 Einleitung, Motivation und Aufbau der Arbeit 2 Stand der Wissenschaft und Technik 2.1 Strahlwerkzeug Laser und dessen Eigenschaften 2.1.1 Der ideale Laserstrahl 2.1.2 Strahlführung und -formung 2.2 Grundlagen des Laserstrahlschweißens 2.2.1 Laserschweißprozess 2.2.2 Laserschweißen von Kupfer- und Aluminiumwerkstoffen 2.2.3 Schweißnahtfehler 2.2.4 Elektrischer Übergangswiderstand einer Laserschweißnaht 2.3 Qualitätssicherung und Prozessüberwachung 2.3.1 Indirekte Prozessüberwachung 2.3.2 Direkte Prozessüberwachung 2.4 Grundlagen der optischen Kohärenztomografie OCT 2.4.1 Einführung und Überblick 2.4.2 Optische Effekte 2.4.3 Michelson-Interferometer 2.4.4 Spectral-Domain OCT 2.4.5 Laterale und axiale Auflösung sowie der Messbereich 2.4.6 Optische Kohärenztomografie beim Laserstrahlschweißen 2.5 Grundlagen der Messtechnik 3 Handlungsbedarf und Zielsetzung 4 Verwendete Systemtechnik und erarbeitete experimentelle Methoden 4.1 Versuchsaufbau und -durchführung 4.1.1 Laserquelle und Bearbeitungsoptik 4.1.2 Optische Kohärenztomografie 4.1.3 Hochgeschwindigkeitskamera 4.1.4 Untersuchte Fügeverbindungen und Versuchsaufbau 4.1.5 Einbringung des Fügespaltes und dessen Auswirkung auf die Einschweißtiefe 4.2 Metallografische Beurteilung der Schweißnahtqualität 4.3 Methoden der Kapillartiefenmessungen und Referenzierung 4.3.1 Punktmessung 4.3.2 Linienscan 4.3.3 Referenzierung der Kapillartiefenmessungen 4.3.4 Optimierung der Verrechnung von Referenz- und Kapillartiefenmessung 4.4 Kalibrierung des OCT 4.5 Positionierung mittels OCT 4.6 Messfähigkeitsanalyse 4.7 Eingrenzung der Einsatzmöglichkeiten des OCT für die Inline-Messung 5 OCT-basierte Schweißnahtbewertungen 5.1 Erarbeitung eines topologischen Modells der Dampfkapillare mittels OCT 5.1.1 Kupfer/Kupfer Schweißverbindung 5.1.2 Kupfer/Aluminium Schweißverbindung 5.1.3 Aluminium/Kupfer Schweißverbindung 5.1.4 Aluminium/Aluminium Schweißverbindung 5.1.5 Zusammenfassung und Gegenüberstellung der Erkenntnisse 5.2 Überführung der Kapillartiefenmessungen auf die metallografische Einschweißtiefe 5.3 Bestimmung der Anbindebreite einer Laserschweißnaht 5.4 Bestimmung der Schweißqualität bei auftretendem Fügespalt 5.4.1 Bestimmung der Messposition für die Punktmessung 5.4.2 Entwicklung von statistischen Kennwerten 5.4.3 Bestimmung der Schweißqualität anhand der Kennwerte 5.5 Diskussion der Ergebnisse 6 Zusammenfassung, Folgerungen und Ausblick 7 Literaturverzeichnis 8 Anhang / With the increasing demand for electrically driven vehicles, battery module production is becoming more important for automobile manufacturers. During battery module production, many battery cells are connected. Through this contacting process, the conductors of the battery cells, which are made of copper or aluminum, are joined together in a material-to-material manner using a laser welding process. With the high number of battery cells to be contacted comes many laser welding processes. The cycle time of a single welding process is less than 60 ms. This results in the need for an in-line Quality Assurance (QA) system. An OCT system based on an optical coherence tomograph could have the potential to fulfill the requirements of an Inline QA system. The system enables for the first time to measure the capillary depth of the laser welding process Inline for battery contacting. Within the scope of this work, it is fundamentally examined whether an OCT system is suitable as a QA system for the laser welding of copper and aluminum. A scanner-based OCT system is used, which allows the OCT measuring beam to be positioned independently around the processing laser beam. This makes it possible to take topological measurements at different points related to the position of the processing laser. It can be measured both at a fixed position within the vapor capillary and on a theoretical scan line. The measurements are always referenced to the component surface. This procedure could be optimized within the scope of this work, both in terms of accuracy and in terms of the number of referencing. The OCT system was also used to detect component positions. In this way, the laser welding process could be optimally positioned, independent of component tolerances, both laterally and in relation to the focus position. In addition, a rudimentary measurement system analysis was conducted as well as an investigation of the application limits of the OCT system for capillary depth measurement. Topological welding process models were created by line scans of the OCT system and using high-speed camera recordings. These process models form the basis for the development of strategies for quality assurance using the OCT system and the focus was set on the effect of a joint gap on the welding quality and the OCT measurements. A methodology for the case without a joint gap occurring is developed and conducted as an example, with which the welding depth can be calculated using the capillary depth measurements of the OCT system. It is also being investigated whether and how the connection width can be determined with the OCT. In addition, a promising approach how the weld quality can be determined when a joint gap occurs is presented. Based on the welding process model developed, three characteristic values to determine the welding quality are extracted from the measurement data.:Verzeichnis der Abkürzungen und Formelzeichen Kurzfassung Abstract 1 Einleitung, Motivation und Aufbau der Arbeit 2 Stand der Wissenschaft und Technik 2.1 Strahlwerkzeug Laser und dessen Eigenschaften 2.1.1 Der ideale Laserstrahl 2.1.2 Strahlführung und -formung 2.2 Grundlagen des Laserstrahlschweißens 2.2.1 Laserschweißprozess 2.2.2 Laserschweißen von Kupfer- und Aluminiumwerkstoffen 2.2.3 Schweißnahtfehler 2.2.4 Elektrischer Übergangswiderstand einer Laserschweißnaht 2.3 Qualitätssicherung und Prozessüberwachung 2.3.1 Indirekte Prozessüberwachung 2.3.2 Direkte Prozessüberwachung 2.4 Grundlagen der optischen Kohärenztomografie OCT 2.4.1 Einführung und Überblick 2.4.2 Optische Effekte 2.4.3 Michelson-Interferometer 2.4.4 Spectral-Domain OCT 2.4.5 Laterale und axiale Auflösung sowie der Messbereich 2.4.6 Optische Kohärenztomografie beim Laserstrahlschweißen 2.5 Grundlagen der Messtechnik 3 Handlungsbedarf und Zielsetzung 4 Verwendete Systemtechnik und erarbeitete experimentelle Methoden 4.1 Versuchsaufbau und -durchführung 4.1.1 Laserquelle und Bearbeitungsoptik 4.1.2 Optische Kohärenztomografie 4.1.3 Hochgeschwindigkeitskamera 4.1.4 Untersuchte Fügeverbindungen und Versuchsaufbau 4.1.5 Einbringung des Fügespaltes und dessen Auswirkung auf die Einschweißtiefe 4.2 Metallografische Beurteilung der Schweißnahtqualität 4.3 Methoden der Kapillartiefenmessungen und Referenzierung 4.3.1 Punktmessung 4.3.2 Linienscan 4.3.3 Referenzierung der Kapillartiefenmessungen 4.3.4 Optimierung der Verrechnung von Referenz- und Kapillartiefenmessung 4.4 Kalibrierung des OCT 4.5 Positionierung mittels OCT 4.6 Messfähigkeitsanalyse 4.7 Eingrenzung der Einsatzmöglichkeiten des OCT für die Inline-Messung 5 OCT-basierte Schweißnahtbewertungen 5.1 Erarbeitung eines topologischen Modells der Dampfkapillare mittels OCT 5.1.1 Kupfer/Kupfer Schweißverbindung 5.1.2 Kupfer/Aluminium Schweißverbindung 5.1.3 Aluminium/Kupfer Schweißverbindung 5.1.4 Aluminium/Aluminium Schweißverbindung 5.1.5 Zusammenfassung und Gegenüberstellung der Erkenntnisse 5.2 Überführung der Kapillartiefenmessungen auf die metallografische Einschweißtiefe 5.3 Bestimmung der Anbindebreite einer Laserschweißnaht 5.4 Bestimmung der Schweißqualität bei auftretendem Fügespalt 5.4.1 Bestimmung der Messposition für die Punktmessung 5.4.2 Entwicklung von statistischen Kennwerten 5.4.3 Bestimmung der Schweißqualität anhand der Kennwerte 5.5 Diskussion der Ergebnisse 6 Zusammenfassung, Folgerungen und Ausblick 7 Literaturverzeichnis 8 Anhang

In dental research, the morphometric assessment of restorations is a challenge. This also applies to the assessment of the length of interfacial adhesive defects in composite restorations as a measure of tooth-restoration bond failure. The determined mean fractions of interfacial gap length on enamel and dentin interfaces deviate from the true means (N → ∞), depending on the number (Ni) of object layers assessed. Cervical composite restorations were imaged with spectral domain optical coherence tomography (SD-OCT). The mean fractions of interfacial gap length on enamel and dentin were determined for an increasing number of OCT cross-sectional images (B-scans) per restoration and were graphically displayed as a function of the number of B-scans. As the number of B-scans increased, the calculated object means approached a range of ±2.5%. This analysis is appropriate for displaying the relationship between the determined mean fraction of interfacial gap length at the enamel/dentin-restoration interface and the number of B-scans.

No description available.

No description available.