First Advisor

Jay Nadeau

Term of Graduation

Winter 2023

Date of Publication


Document Type


Degree Name

Doctor of Philosophy (Ph.D.) in Applied Physics







Physical Description

1 online resource (xi, 144 pages)


Digital holographic microcopy (DHM) is a label-free technique that has gained attention in recent years as a tool for volumetric imaging. One application of DHM is for the study of microbial motility with the advantage being that organisms may freely move within their environment. Images created from DHM are in the form of holograms. Holograms are time recordings showing XY information with the Z information contained within. Z information can be retrieved from the holograms directly through a variety of numerical techniques or through reconstruction. Datasets generated from DHM are large and processing remains a challenging task. Here, we show how following reconstruction, the refocusing method can be used to locate particles manually through Z. We note the difference between the lateral and axial resolutions and show the impact of the point-spread functions on resolving data. We show that 2D tracking of organisms is generally sufficient for quantifying motility though specific applications such as surface behavior still require 3D information. With this understanding, we shift to studying the microgravity environment. The microgravity environment is the weightless environment of the space station. It is difficult to conduct experiments on the space station, so we simulate certain characteristics of that environment on Earth by using simulated microgravity devices. We review bacterial responses to microgravity and the simulated microgravity environment with an emphasis on motility and chemotaxis. Finally, we apply the techniques developed in this thesis to study the simulated microgravity environment by examining the motility and chemotaxis of Vibrio alginolyticus. We show that while there was little change in motility between simulated microgravity and normal gravity, there is a statistically significant difference in cloud sizes. Future work would involve comparing these responses with the actual microgravity environment.


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