Focusing Properties of Vectorial Optical Fields and Their Applications

Date of Award

2022

Degree Name

Ph.D. Electro-Optics

Department

Department of Electro-Optics

Advisor/Chair

Qiwen Zhan

Abstract

Vectorial optical fields are a type of structured optical fields with inhomogeneous polarization distribution. They are referred to be inhomogenously polarized optical fields due to the fact that different locations across the wavefront have different state of polarizations (SOP). Cylindrical vector (CV) beams are considered one special class of vectorial optical fields where the polarization states are arranged with cylindrical symmetry in the beam cross section. Plenty of unique properties originated from their special intrinsic symmetry have distinguished the vectorial fields from general optical beams with homogeneous polarization. When such beams are focused by a high numerical aperture (NA) objective lens, focal field properties have led to many applications including but not limited to particle manipulation, optical nanofabrication, beam shaping and optical imaging. In addition, the properties of spin and orbital angular momentum at the focus of vectorial fields have been an attractive area of interest, which may have considerable potential applications including, optical tweezers, light-matter interaction, and particle trapping. This dissertation consists of an experimental part and numerical part. In the experimental part, I will describe an experimental setup to generate vectorial optical fields with complex intensity distribution and engineered polarization pattern. The experimental setup is called Vectorial Optical Field Generator (VOF-Gen), which is capable of generating an optical field with arbitrarily independent controls of phase, amplitude, and polarization on the pixel level utilizing high resolution reflective phase-only liquid crystal (LC) spatial light modulator (SLM). Experimental results will be presented, where various vectorial optical fields containing phase, amplitude, polarization modulations are successfully demonstrated. In the numerical part, I will introduce a numerical model for the so-called 4Pi microscopic focusing system. Full mathematical description and numerical analysis using this system will be discussed in detail for calculating and focusing of vectorial optical fields. The 4Pi microscopic system will be used to calculate vectorial optical fields with structured intensity and polarization at the pupil plane when a dipole emitter is positioned at the focus point. Notably, when the problem is reversed and the engineered pupil plane vector fields are used to illuminate the system, many focusing properties can be explored under tailoring the two-counter propagating beams using the 4Pi microscopic focusing system. For example, designing an optical spot with three-dimensional homogenized intensity structure can be obtained at the focus if electric and magnetic dipoles are placed to oscillate at the focal point. Further focusing investigation on the complex behavior of the optical angular momentum at the focal point will be explored when vector fields are focused with various focusing and incident beam conditions.

Keywords

Engineering, Vector Fields, Polarization of Light, Microscopic Focusing, Optical Angular Momentum, Light beam shaping, Modulation of Light

Rights Statement

Copyright © 2022, author

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