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Title:Optical polarization control in free space and through random media using wavefront shaping
Author(s):Tripathi, Santosh
Director of Research:Toussaint, Kimani C.
Doctoral Committee Chair(s):Toussaint, Kimani C.
Doctoral Committee Member(s):Makela, Jonathan J.; Ravaioli, Umberto; Schutt-Ainé, José E.
Department / Program:Electrical & Computer Eng
Discipline:Electrical & Computer Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):wavefront shaping
random media
light propagation
photodynamic therapy
3D fabrication
Abstract:Light is widely used in areas such as optical communications, micro/nano fabrication, industrial process control, material characterization, and biomedical imaging. The usefulness of light in these areas depends on the dexterity with which the state of the optical field, defined by the spatio-temporal distribution of the field's phase, intensity, polarization and coherence, can be controlled and delivered to the required spatio-temporal position. In this thesis, we present two novel techniques to control the polarization of light, one for light propagating in free space and the other for light that is transmitted through highly scattering material. The former is useful in the characterization of materials and structures lying on the surface whereas the later, with further development, has potential to be useful in 3D IC fabrication/characterization, deep tissue imaging, and photodynamic therapy of diseases. The first technique relates to the generation of vector beams, which possess a spatially varying distribution of polarization according them with many interesting properties. However, the majority of techniques reported in the literature to generate vector beams employ interferometers, thereby limiting the stability of the beams generated. By using the polarization rotation behavior of nematic liquid crystal spatial light modulators (SLMs) and a specially designed optical setup, we develop a system that can generate a wide variety of vector beams without using interferometers. We also show that the diversity of polarization present in vector beams can be advantageously used in a variety of material characterization problems. Specifically, we show that the diversity of polarization can be used to expedite the characterization of thin films in ellipsometric measurements and improve the robustness of characterization in the measurement of the elements of the second-order nonlinear susceptibility tensor of single nanoparticles. The second technique relates to controlling the state of light transmitted through highly scattering media. In this regard, we introduce the concept of the vector transmission matrix (VTM) by generalizing the conventional transmission matrix. We develop a novel technique to measure the absolute value of VTM elements and show that the randomness of the medium can be used as a resource in controlling the phase, amplitude and polarization of the transmitted light and demonstrate the first ever quantitative control over these parameters. The majority of our experiments in scattering media rely on the use of a phase-only SLM that we designed using Texas Instruments' DLP LightCrafter evaluation module which currently costs less than \$600. It is well known that the spatially dependent modulation of an optical field's phase enables many novel applications; however, phase-only SLMs are expensive optical components and as a result are not yet widely used. The low-cost, phase-only SLM customized and presented in this thesis has the potential to change this situation thereby helping advancements in the field.
Issue Date:2014-01-16
Rights Information:Copyright 2013 Santosh Tripathi
Date Available in IDEALS:2014-01-16
Date Deposited:2013-12

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