Microelectronic devices are multilayered structures with many different interfaces. Their mechanical reliability is of utmost importance when considering the implementation of new materials. Linear elastic fracture mechanics (LEFM) is a common approach that has been used for interfacial fracture analyses in the microelectronics industry where the energy release rate parameter is considered to be the driving force for delamination and the failure criterion is established by comparing this with the interface toughness. However this approach has been unable to model crack-nucleation, which plays an important part in analyzing the mechanical reliability of chip-package systems. The cohesive interface modeling approach, which is considered here, has the capability to model crack nucleation and growth, provided interfacial parameters such as strength and toughness of the system are available. These parameters are obtained through the extraction of traction-separation relations, which can be obtained through indirect hybrid numerical/experimental methods or direct experimental methods. All methods of extracting traction-separation relations require some local feature of the crack-tip region to be measured. The focus in this doctoral work has been on the comparison of the two methods for a mode-I DCB experiment and on the development of a universal loading device to extract mixed-mode traction-separation relations at different mode-mix values. The techniques that have been adopted for the local measurements are infrared crack opening interferometry (IR-COI) and digital image correlation (DIC). Apart from the global measurements of load-displacement (P-[delta]), local crack-tip parameters were measured using IR-COI or DIC. The combination of global and local measurements gave the relations between the fracture driving force (energy release rate or J-integral, J) and crack opening displacements, which were used to obtain the local tractions. IR-COI is an extremely useful technique to image and measure local crack-tip parameters. However, as IR-COI is restricted to normal measurements, the loading device was configured to accommodate a DIC system in order to make both normal and tangential measurements. In addition to measurements, fracture surface characterization techniques such as atomic force microscopy (AFM), profilometry and X-ray photoelectron spectroscopy were used to observe the fracture mechanisms. / text

Understanding material behavior under extreme conditions is an important area of research in physics and material science. One method to study the behavior of materials under these conditions is to drive a strong shock wave through a material and watch its response. In many cases the material response is complicated by phase transitions such as lattice restructuring (Barker 1975; Mabire and Hereil 2000; Swift, Tierney et al. 2005) and melting (Asay 1975; Elias, Chapron et al. 1988; Werdiger, Eliezer et al. 1999; Mabire and Hereil 2000; Swift, Tierney et al. 2005). To study these dynamics we are using lasers in high time resolution pump-probe experiments to develop a real time diagnostic on the phase of a shocked material. This technique enables probing of the entire phase history of a material as it shock compresses and releases. In addition to linear reflectivity and ultra-fast 2D displacement interferometry, we developed a melting diagnostics based on the non-linear optical technique of third harmonic generation (THG) using a circularly polarized laser pulse. This diagnostic resolves the less than 300 fs melting transition of laser excited Si and GaAs, and it also detects a response in shock compressed silicon. Our results show that Si remains crystalline during compression of an elastic 100 kbar shock wave. Results from Si shocked to higher pressures (> 300 kbar) indicate a decrease in THG, suggesting some level of disordering or unexplained phase change. / text

The fractional quantum Hall (FQH) effect harbors a wealth of unique phenomena, many of which remain mysterious. Of particular interest is the predicted existence of quasi-particles with unusual topological properties, especially in light of recent proposals to observe these properties using electronic interferometers. An introduction to quantum Hall physics and electronic interferometry is given in Chapter 1 of this thesis. The remaining chapters, summarized below, describe a set of experiments in which FQH systems are studied using electronic Fabry-Perot interferometry and related techniques. Since prior studies of electronic Fabry-Perot interferometers revealed unexpected behavior even in the integer quantum Hall (IQH) regime, we began our measurements there. Our initial experiment, presented in Chapter 2, disentangles signatures of Coulomb interaction effects from those of Aharonov-Bohm (AB) interference and provides the first measurement of pure AB interference in these devices. In our next experiment, presented in Chapter 3, we measure AB interference oscillations as a function of an applied dc bias, use their period to study the velocity of the interfering electrons, and study how the oscillations decay as a function of bias and magnetic field. Moving to the FQH regime, applying a similar-sized bias to a quantum point contact leads to long-lasting changes in the strengths and positions of FQH plateaus. The involvement of lattice nuclear spins in this effect, suggested by the long persistence times, is confirmed using NMR-type measurements. Although the exact physical process responsible for the effect remains unclear, its filling-factor dependence provides a striking illustration of composite fermion physics. These measurements are described in Chapter 4. In certain devices, interference oscillations associated with several FQH states are observed. Interpretation of their magnetic-field and gate-voltage periods provides a measurement of quasi-particle charge, and temperature dependence measurements suggest differences between the edge structure of IQH and FQH states. These measurements are described in Chapter 5. Finally, Chapter 6 presents some recent, not-yet-published observations that may shed light on ways to improve the visibility of existing oscillations and potentially observe interference at additional FQH states. This chapter concludes with a discussion of possible next steps toward achieving these goals. / Physics

Since 2004, table-top laser-plasma accelerators (LPAs) driven by ˜30fs terwatt laser pulses have produced colimated, nearly mono-energetic eletron bunches with energy up to 1 GeV in laboratories around the world. Large-scale computer simulations show that LPAs can scale to higher energy while retaining high beam quality, but will require laser pulses of higher energy and longer duration than current LPAs. The group of Prof. Mike Downer, in collaboration with the Texas Petawatt (TPW) laser team headed by Prof. Todd Ditmire, is setting up an experiment that uses the TPW laser (1.1 PW, 150 fs) to drive the world’s first multi-GeV LPA. This thesis provides a general overview of the TPW-LPA project, including several diagnostic systems for the beam, plasma and laser pulse. Special attention is given to three of the diagnostic systems: (1)A transverse interferometry diagnostic of the plasma density profile created by the TPW laser pulse; (2)A Thomson scattering diagnostic of the self-guided path of the TPW laser pulse through the plasma; (3)An optical transition radiation diagnostic of the accelerated electron bunch exiting the plasma. In each case, basic principles, theoretical background, calculation and simulation results, and preliminary experimental results will be presented. / text

No description available.

The cornea is the anterior most surface of the eye and plays a critical role in vision. A thin fluid layer, the tear film, coats the outer surface of the cornea and serves to protect, nourish, and lubricate the cornea. At the same time, the tear film is responsible for creating a smooth continuous surface where the majority of refraction takes place in the eye. A significant component of vision quality is determined by the shape of the cornea and stability of the tear film. It is desirable to possess an instrument that can measure the corneal shape and tear film surface with the same accuracy and resolution that is currently performed on common optical elements. A dual interferometer system for measuring the dynamic corneal topography is designed, built, and verified. The completed system is validated by testing on human subjects. The system consists of two co-aligned polarization splitting Twyman-Green interferometers designed to measure phase instantaneously. The primary interferometer measures the surface of the tear film while the secondary interferometer simultaneously tracks the absolute position of the cornea. Eye motion, ocular variation, and a dynamic tear film surface will result in a non-null configuration of the surface with respect to the interferometer system. A non-null test results in significant interferometer induced errors that add to the measured phase. New algorithms are developed to recover the absolute surface topography of the tear film and corneal surface from the simultaneous interferometer measurements. The results are high-resolution and high-accuracy surface topography measurements of the in vivo cornea that are captured at standard camera frame rates. This dissertation will cover the development and construction of an interferometer system for measuring the dynamic corneal topography of the human eye. The discussion starts with the completion of an interferometer for measuring the tear film. The tear film interferometer is part of an ongoing research project that has spanned multiple dissertations. For this research, the instrument was tested on human subjects and resulted in refinements to the interferometer design. The final configuration of the tear film interferometer and results from human subjects testing are presented. Feedback from this instrument was used to support the development and construction of the interferometric corneal topographer system. A calibration is performed on the instrument, and then verified against simulated eye surfaces. Finally, the instrument is validated by testing on human subjects. The result is an interferometer system that can non-invasively measure the dynamic corneal topography with greater accuracy and resolution than existing technologies.

Optical testing often requires a measurement of the phase difference between light from two different optical systems. One system is a master or reference system, and the other is a sample or test system. In the optical shop, the reference may be a precision optical surface and the test system may be a newly fabricated surface. A computer generated hologram is a geometric pattern that can be used as a precise reference in an optical test. Computer-generated holograms can be used to make reference systems that would be very difficult to make by other methods. Various encoding methods for making computer-generated holograms are discussed, and a new method is presented that can easily be used on image recorders intended for image processing applications. This general encoding method has many characteristics in common with earlier computer-generated holograms. Examples are given to demonstrate the properties of synthetic holograms and the differences among different encoding techniques. Geometric ray tracing is an essential part of the process of developing holograms for optical systems. A computer ray-trace code was developed to model the optical performance of equipment used in optical testing. This program was used to obtain numeric coefficients that describe the optical properties (optical path) needed to define a reference wavefront. A review of interferometer design leads to a discussion of how the hologram functions as a part of the interferometer and of the limitations to the computer-generated hologram. The diffraction pattern from the hologram, observed in the focal plane of a lens, is the key to understanding the use and limitations of the hologram in an interferometer. A detailed prescription is given for making a computer-generated hologram for a commercial interferometer designed for use with holograms. Problems of finding the proper focal point, the correct hologram size, and preparation of the final hologram image are discussed. An example of an actual test is included. Finally, an analysis of various errors encountered and the limitations of the methods used is presented. Within these limitations, computer-generated holograms can easily and routinely be used to test aspheric optical components.

Atom-surface interactions are becoming an integral part of the field of atom optics. Here the role of van der Waals atom-surface interactions in atom wave diffraction and interferometry are investigated. In particular, it is shown that van der Waals interactions influence the intensity and phase of atomic diffraction patterns obtained from material gratings. As a result the atomic diffraction patterns are utilized to make an accurate determination of the interaction strength and verify the spatial variation of the atom-surface potential. A theory for describing the modified atom wave diffraction patterns is developed through an analogy with optical waves. An atom interferometer is used to directly measure the de Broglie wave phase shift induced by atom-surface interactions. More specifically, the phases of the zeroth, first, and second diffraction orders are measured. A proposal for using electromagnetic fields to modify the van der Waals interaction is put forth. Several of the important experimental components for observing such an effect are also demonstrated.

Background and Rationale: Reproductive dysfunction affects more than 15% of Canadian women; however, the underlying causes remain largely unknown. Ultrasonography is the most commonly used research and diagnostic tool for imaging the ovaries and uterus. However, current ultrasonographic techniques allow the detection of ovarian structures (eg. follicles, corpora lutea) at diameters of only ≥2 mm. The increased effectiveness of synchrotron technology for imaging ovaries in comparison to conventional imaging methods is currently unknown. Overall Objective: The overall objective of this research was to determine the effectiveness of synchrotron techniques for imaging ovaries. We hypothesized that synchrotron techniques would provide greater contrast for visualizing structural details of follicles, corpora lutea (CL), and cumulus oocyte complexes (COC), compared to conventional ultrasonography. Materials and Methods: Three studies were conducted to evaluate phase-contrast based synchrotron imaging methods. The first study involved Diffraction Enhanced Imaging (DEI) of bovine ovaries (n=6). The second study involved Propagation-Based Computed Tomography (PB-CT) imaging of bovine (n=4) and human ovaries (n=4). A third, preliminary study was conducted to explore the use of Talbot Grating Interferometry (TGI-CT) imaging of bovine (n=1) and human ovaries (n=1). Fresh and formalin-fixed bovine and human ovaries were imaged without or with contrast injection into the ovarian artery. Following synchrotron imaging, all ovarian samples were evaluated using diagnostic ultrasonography and histology. Images obtained using synchrotron techniques, ultrasonography and histology were qualitative and quantitatively compared. Results: DEI allowed the identification of 71% of follicles ≥2 mm and 67% of CL detected using ultrasonography. Mean follicle diameter was similar between DEI (9.6 ± 2.4 mm), ultrasonography (9.0 ± 2.6 mm), and histology (6.9 ± 1.9 mm) for fresh ovaries without contrast (P = 0.70). Likewise, no difference in CL diameter was detected between DEI (11.64 ± 1.67 mm), ultrasonography (9.34 ± 0.35 mm), and histology (9.6 ± 0.4 mm), (P = 0.34). Antral Follicle Count (AFC; ≥2mm) was similar between ultrasonography (6.5 ± 0.7 mm, fresh with no contrast; 6.5 ± 2.5 mm, preserved with no contrast) and DEI ( 4.5 ± 0.5 mm, fresh with no contrast; 6.5 ± 0.50 mm, preserved with no contrast) (P > 0.05). However, the contrast resolution for differentiating follicles and CL was inferior with DEI compared to ultrasonography. Small antral follicles <2mm, cell layers comprising the follicle wall and COC were not detected using either DEI or ultrasonography. PB-CT imaging enabled the visualization of 100% of follicles ≥2 mm and 100% of CL that were detected with ultrasonography. CL containing a central cystic cavity were identified using PB-CT; however, CL without a central cystic cavity were not well-visualized. Mean follicle and luteal diameters did not differ among PB-CT, ultrasonography and histology (P>0.05). PB-CT was superior to ultrasonography for detecting small antral follicles <2 mm in bovine ovaries (P = 0.04), and the granulosa and theca cell layers of the follicle wall in bovine and human ovaries (P < 0.0001). However, TGI-CT images exhibited greater contrast resolution for visualizing small and large antral follicles, CL, and the cell layers of the follicle wall compared to both PB-CT and ultrasonography. High contrast structures resembling COC were detected with both PB-CT and TGI-CT, but not with ultrasonography. Only TGI-CT permitted the visualization of the oocyte within the COC in fresh and preserved ovaries. Conclusions: DEI was inferior to ultrasonography for detecting ovarian follicles and CL. PB-CT was superior to ultrasonography for visualizing follicles <2 mm, COC, and the cell layers of the follicle wall. However, PB-CT was as effective as ultrasonography for detecting and measuring follicles ≥2 mm and cystic CL. Preliminary findings suggest that TGI-CT provides the greatest contrast for imaging both ovarian macro- and microanatomy compared to PB-CT, DEI, and ultrasonography.

This work is focused on the aerodynamics for a proprietary laminar flow airfoil for Unmanned Aerial Vehicle (UAV) applications. The two main focuses are (1) aerodynamic performance at Reynolds number on the order of 10,000, (2) the effect of a conventional hot-wire probe on laminar separation bubbles. For aerodynamic performance, pressure and wake velocity distributions were measured at Re = 40,000 and 60,000 for a range of angles of attack. The airfoil performed poorly for these Reynolds numbers due to laminar boundary layer separation. 2-D boundary layer trips significantly improved the lift-to-drag ratio. For probe effects, three Reynolds numbers were investigated (Re = 100,000, 150,000, and 200,000), with three angles of attack for each. Pressure and surface shear distributions were measured. Flow upstream of the probe tip was not affected. Transition was promoted downstream due to the additional disturbances in the separated shear layer.