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Title:Diffraction phase microscopy for applications in materials science
Author(s):Edwards, Christopher
Director of Research:Goddard, Lynford L.
Doctoral Committee Chair(s):Goddard, Lynford L.
Doctoral Committee Member(s):Popescu, Gabriel; Cunningham, Brian T.; Boppart, Stephen A.
Department / Program:Electrical & Computer Eng
Discipline:Electrical & Computer Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
biodegradable electronics
defect inspection
white light
diffraction phase microscopy
quantitative phase imaging
Abstract:Quantitative phase imaging (QPI) is a flourishing new field which has recently found tremendous success in the life sciences. QPI utilizes not only the amplitude of the imaging field, but also its phase, in order to provide quantitative topographical and/or refractive index data. As fields from the source interact with the specimen, a fingerprint of the sample’s structure is encoded into the phase front of the imaging field, which can then be used to reconstruct a map of the sample’s surface at the nanoscale. Unfortunately, cameras and detectors only respond to intensity. For this reason, a wide variety of QPI techniques have been developed over the years in order to gain access to this valuable phase information. Diffraction phase microscopy (DPM) utilizes a compact Mach-Zehnder interferometer to combine many of the best attributes of current QPI methods. This compact configuration is common-path which inherently cancels out most mechanisms responsible for noise and is single-shot meaning that the acquisition speed is limited only by the speed of the camera employed. This technique is also non-destructive and does not require staining or coating of the specimen. This unique collection of features enables the DPM system to accurately monitor the dynamics of various nanoscale phenomena in a wide variety of environments. Our DPM system has been used to monitor wet etching, photochemical etching, dissolution of biodegradable electronic materials, expansion and deformation of thin-films and microstructures, and surface wetting and evaporation. It has also been used in semiconductor wafer defect detection. Imaging systems using white light illumination can exhibit up to an order of magnitude lower noise than their laser counterparts. This is a result of the lower coherence, both spatially and temporally, which reduces noise mechanisms such as laser speckle. Unfortunately, white light systems also exhibit additional object-dependent artifacts, like the well-known halo effect, that are not present in their laser counterparts. Recently, we have shown that such artifacts are due to a high-pass filtering phenomenon caused by a lack of spatial coherence. This realization allowed us to quantitatively model the phase reductions and halo effect, and remove them using a variety of techniques. The final DPM/wDPM system is capable of providing halo-free images of structures typical in both materials and life science applications and operates in both transmission and reflection modes in order to accommodate both transparent and opaque samples alike. The DPM/wDPM system can be implemented as an add-on module that can be placed at the output port of any conventional light microscope. The user can easily switch between laser and white light sources, as well as transmission and reflection, simply by flipping switches on the microscope. Furthermore, the spatial coherence for white light DPM (wDPM) can be optimized for the given application by rotating the condenser turret in transmission, or adjusting the slider for the aperture diaphragm in reflection, which contain different size pinholes, allowing for a tradeoff between accuracy and speed. The setup also includes an automatic pinhole alignment system, real-time phase imaging, and a graphical user interface (GUI) to make it as user-friendly as possible. The final system was built in the Imaging Suite in Beckman Institute for Advanced Science and Technology to serve as a multi-user inspection/characterization tool that will create a major pipeline for high-impact projects and publications in a variety of fields.
Issue Date:2015-01-21
Rights Information:Copyright 2014 Christopher Edwards
Date Available in IDEALS:2015-01-21
Date Deposited:2014-12

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