Exploiting Speckle to Image Deeper in Scattering Media

Citation

Cua, Eunice Michelle Chua (2022) Exploiting Speckle to Image Deeper in Scattering Media. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/rcsj-a410. https://resolver.caltech.edu/CaltechTHESIS:09152021-000948244

Abstract

Optical methods for imaging and focusing are advantageous in many scenarios as optics can provide exquisite spatial resolution, has multiple sources of contrast, and does not impart ionizing radiation. However, optical scattering remains a fundamental challenge which limits the depth at which we can perform imaging with good spatial resolution. This challenge motivated our investigations into methods that could make use of the scattered light in order to extend the depth of imaging through or within scattering media. In particular, we focus on answering: (1) Can one 'unscramble' the scattered light in order to recover information about the otherwise hidden object?; and (2) Can we preferentially detect the more forward scattered photons in an efficient manner in order to allow deeper penetration with modest resolution? These two questions are explored in the first two projects of the thesis:

1. The development of an imaging system that detects the scattered light and exploits correlations within the scattering process to enable imaging through scattering media at diffraction-limited resolution.

2. The introduction of a novel method, termed Speckle-Resolved Optical Coherence Tomography, that sensitively and preferentially detects the more forward scattered photons in a coherent, speckle-resolved fashion to allow deeper imaging at moderate resolution.

Optical methods offer the benefit of visualizing samples that would otherwise appear transparent. Using light, one is able to visualize and measure the thickness of transparent films and coatings in a non-contact manner. The third project in my thesis focuses on using light to non-destructively visualize and characterize the evenness of the silicone oil layer that typically coats the inner surface of prefilled syringes. Characterizing the evenness of this silicone oil layer is important as it impacts the functionality of the prefilled syringe and may correlate with particle formation, which is undesirable as the number of particles in a syringe is regulated due to potential health concerns.

Thesis Files