Date of Award

8-2020

Document Type

Campus Access Thesis

Degree Name

Master of Science (MS)

Department

Physics, Applied

First Advisor

Chandra S. Yelleswarapu

Second Advisor

Mohamed A. Gharbi

Third Advisor

Jonathan Celli

Abstract

Quantitative phase imaging (QPI) has emerged as viable technique for investigating biological and biomedical samples in its natural environment. Contrary to well established phase microscopes, QPI provides phase maps of the optical path length delays introduced by the specimen. Building on our prior technology of Fourier phase contrast microscopy technique, this thesis work presents a low-¬cost and robust quantitative Fourier phase contrast microscopy (qFPCM) system that can easily be attached to most commercial brightfield microscopes. This is derived by merging the FPCM technique with phase shifting interferometry. By applying three recalibrated voltages across a liquid crystal cell, Stokes parameters are obtained to quantitatively unwrap the object information. To improve the utility of the phase unwrapping, three different textures of nematic liquid crystals were considered. A dye¬-doped nematic liquid crystal (NLC) cells sandwiched between two ITO coated glass substrates, where orientations of the LC molecules are aligned based on the polymerization conditions on both input and output interfaces of the cells. The three LC cell prepared were planar (anti-parallel), twisted and hybrid. An electro¬optic modulation was used to measure the phase retardation of the LC cells with respect to applied voltage. The phase difference between the diffracted and undeviated beams were measured to be 0.763π for hybrid NLC texture, 0.746π for twisted NLC texture and 0.690π for planar NLC texture their corresponding phase difference between two detector points were ΦPNLC = 0.449, ΦTNLC = 0.486, and ΦHNLC = 0.497. These phase difference parameters indicate that in HNLC texture, there is more tolerance with voltage control than in TNLC and PNLC textures. The spaces between each detector points of the hybrid cell are widely apart as compared to that of the planar and twisted cells. To simulate transparent biological sample, 10¬-30 µm microspheres were immersed in glycerol and sandwiched between two cover slips. The sample was imaged and its optical pathlength quantitatively measured to study the accuracy and sensitivity to small phase changes of the qFPCM system. The refractive index contrast achieved between the sample and its surrounding medium was 0.047. Due to the orientation of the LC cells under applied voltage from 0V to 2V, the hybrid cell showed a higher contrast of the image, meaning that the hybrid texture is the best phase contrast filter.

Comments

Free and open access to this Campus Access Thesis is made available to the UMass Boston community by ScholarWorks at UMass Boston. Those not on campus and those without a UMass Boston campus username and password may gain access to this thesis through resources like Proquest Dissertations & Theses Global or through Interlibrary Loan. If you have a UMass Boston campus username and password and would like to download this work from off-campus, click on the "Off-Campus UMass Boston Users" link above.

Download
Off-Campus UMass Boston Users

Share

COinS