Master of Science (M.S.), University of Dayton, 2016, Electrical Engineering

The photorefractive effect is a nonlinear optical effect that refers to change in refractive index of a material when it is illuminated by light. When illuminated by an interference pattern of coherent light source, this PR effect is responsible for two-beam coupling in PR materials, sometimes leading to energy exchange between the beams. PR materials can also be used as holographic storage media. In fact, dynamic real-time holographic interferometry can be implemented using photorefractive materials. To achieve this, two beams, one called the pump and one called the object beam, are introduced onto a photorefractive material to write the hologram of the object. During the hologram writing process, these beams can couple in intensity and/or phase which thereafter are responsible for self-diffraction of these beams, and can also give rise to Bragg and non-Bragg orders. The information from the Bragg and non-Bragg orders plays an important role in determining the 3D information of the object. In this thesis, an exact study is performed to examine the spatial evolution of Bragg and non-Bragg orders in photorefractive iron doped lithium niobate for different types of beam profiles such as Gaussian and flattops using an angular plane wave spectral decomposition technique. For Gaussian beam incidence, it has been found that higher or non-Bragg orders shows evidence of mode conversion of incident beam profiles. The numerical technique developed in this work should be useful in determining the phases of the Bragg and non-Bragg orders which have applications in dynamic phase-shifting digital holography and holographic interferometry.

Committee: Partha Banerjee Dr (Committee Chair); Monish Chatterjee Dr (Committee Member); Joseph Haus Dr (Committee Member) Subjects: Electrical Engineering; Optics

Doctor of Philosophy (Ph.D.), University of Dayton, 2015, Electro-Optics

Materials exhibiting effective nonlinearity through refractive index modulation at relatively low optical powers can be exploited for various applications. Examples of such materials include liquids where the refractive index is modified through heating, and photorefractives where the refractive index modulation is caused by the induced space charge field due to optically generated charges and their redistribution. Optical probing techniques of these and related effects include digital holography, holographic interferometry, and diffraction. First, the effect of self-phase modulation of a focused laser beam in a thermal medium such as a liquid is studied using a low power probe beam. Beyond self-phase modulation, thermal blooming occurs, due to bubbles generated in the liquid. These bubbles are characterized using the same probe and digital holography. An application of these bubbles to nanoparticle agglomeration and transport for drug delivery systems is proposed. Next, the use of recording materials such as photorefractive lithium niobate for implementing real-time phase shifting holographic interferometry is examined in detail. Holographic interferometry is a convenient tool for 3D characterization of deformations of an object. The hologram of an object is first written in the material using a reference beam, and then read out by the same reference beam and light from the deformed object. It is shown that the use of both Bragg and non-Bragg orders during conventional two-beam coupling in a photorefractive material facilitates the simultaneous generation of phase shifts necessary for this type of holographic interferometry. In certain applications involving liquid crystals, the spatial modulation of the director axis can yield improved energy coupling in hybrid liquid crystal – photorefractive devices. Nanoscale engineering of the director axis is possible using the surface corrugation in photorefractives induced by the space charge field through the piez (open full item for complete abstract)

Committee: Partha Banerjee Dr. (Committee Chair); Joseph Haus Dr. (Committee Member); Andrew Sarangan Dr. (Committee Member); Sergei Lyuksyutov Dr. (Committee Member); Georges Nehmetallah Dr. (Committee Member) Subjects: Engineering; Optics