Near-Field Induced Polarization Imaging for Optical Data Storage Metrology
It is shown that when the induced polarization is used to acquire near-field induced polarization images, both a high-resolution near-field image and height information of the object are obtained
Induced Polarization Imaging and Other Topics Associated with the Solid Immersion Lens
An induced evanescent polarization imaging system and associated topics using a solid immersion lens (SIL) are demonstrated in this dissertation. The physics and properties of induced polarization signal of the SIL are studied by both simulations and experiments. In the SIL optical system, with a linearly-polarized incident illumination light at the entrance pupil, an orthogonal component of polarization is induced upon reflection from the SIL. This orthogonal polarization signal contains information of both air gap height h between the bottom of the SIL and the top surface of the sample. It is used as the air gap control signal in the SIL system. An experimental SIL near-field microscope setup is developed and demonstrated. A compact mechanical package is developed for a standard microscope that implements a SIL on a retractable bimorph swing arm. With the compact package mounted on an inverted microscope, far-field and near-field images are obtained at the same location by moving the SIL with the swing arm. A 25 μm diameter and 0.8 μm high circular pedestal in the center of the flat portion of the SIL is fabricated, along with a conically shaped surrounding region. The image contrast enhancement, high lateral resolution and height information are obtained with induced polarization evanescent imaging using SIL. Experiments are conducted by imaging features on a patterned Si substrate. Imaging theory is used to predict optimum orientation of high-spatial-frequency samples, and a topographical image is derived from the induced polarization image through a calibration procedure. A
Numerical analysis of surface crack propagation in flexible pavements using XFEM and cohesive zone model
Surface initiated (top-down) cracking in the longitudinal direction of pavements has become a predominant mode of failure in thick asphalt pavements. Most previous researchers studied crack propagation using the traditional Linear Elastic Fracture Mechanics (LEFM) method by calculating the stress intensity factor around the crack tip. In this paper, Extended Finite Element Method (XFEM) was used to study the key factors causing surface initiated crack propagation under surface tension and/or shear. A two-dimensional (2-D) finite element (FE) model for a two-lane flexible pavement was built to predict pavement responses and crack propagation potential under various scenarios. It was found that surface tension is the major driving force for crack propagation when the crack is at some distance away from tire loading. The results show that the distance from the location of crack to tire loading, the depth and direction of the crack, and the modulus ratio between the hot-mix asphalt (HMA) layer and the base layer have significant influences on crack propagation under surface tension. On the other hand, this study shows that shear stress can induce surface initiated crack propagation near the loading area as the shear resistance of material becomes low at the high temperature.