Dealing with Imperfections: From Aberration to Scattering

Citation

Cao, Ruizhi (2024) Dealing with Imperfections: From Aberration to Scattering. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/adgc-g315. https://resolver.caltech.edu/CaltechTHESIS:02152024-233300684

Abstract

Optical imaging has gained popularity in life science, biomedical imaging, fundamental physics research, and various other fields due to its non-invasive nature. In a carefully designed optical instrument operating in an ideal environment, the resolution of the optical imaging system is defined by its numerical aperture. However, practical manufacturing issues and inaccurate lens models make it challenging to achieve high resolution across a large area. High magnification lenses introduce aberrations that degrade image quality, prompting the use of complex lens systems dedicated to mitigating such aberrations. Furthermore, when a scattering medium is introduced into the imaging system, image formation becomes infeasible as light follows a complicated trajectory. These challenges pose great obstacles to the use of optical imaging methods in various scenarios. This thesis primarily consists of two parts, one aims to deal with aberration and the other tries to solve scattering induced imaging problems.

In the first part of my thesis, I will discuss a technique called APIC (Angular Ptychographic Imaging with Closed-form method), which enables high-resolution imaging across a large field of view. To make APIC applicable in many non-ideal cases where aberrations (such as defocus) degrade image quality, we equip APIC with a closed-form aberration correction algorithm. We will demonstrate that APIC is unprecedentedly robust against aberrations and can retrieve high-resolution complex light fields using low magnification objectives.

In the second part, we move on to dealing with scattering induced imaging problems. To form images where a scattering medium is present, we first explore the application of ultrasound modulation in optical imaging. We show that, by using ultrasound, we can image a hidden object in a highly scattering medium with ultrasonic resolution. Although this technique helps obtain clear images in the presence of a scattering medium, its resolution is limited. We then demonstrate a method in addressing another scattering problem, namely the non-line-of-sight (NLOS) imaging problem. In a general NLOS problem, modulation mechanisms such as the aforementioned ultrasound modulation are infeasible. We demonstrate that light can be directly focused on the hidden target with an optical diffraction-limited resolution by exploring the properties of the hidden target itself. We will show that this active focusing method possess remarkably improved resolution compared to existing methods and is able to image objects with large reflectance differences.

Thesis Files