Optical quantitative phase microscopy: novel methods and applications

Quantitative Phase Imaging (QPI) techniques are a set of microscopy techniques that
allow us to observe transparent samples, such as biological cells and optical
components, in a way that standard optical microscopes cannot. Although these
samples do not absorb light they do cause a significant change to the phase of the
incident light. QPI techniques map these optical path length variations across a
transparent sample to produce high contrast phase images. Additionally, the
quantitative nature of the phase images allows for further information, such as sample
thickness and refractive index, to be deduced. The purpose of this thesis is to develop
and test novel QPI methods and applications based on a diffractive imaging technique
called ptychography.
The thesis starts with an overview of key QPI techniques before showing the
development and testing of a novel QPI technique called optical near-field
ptychography. The phase image produced is shown to be accurate and artefact free,
while reducing the quantity of data needed for image acquisition, when compared to
existing techniques.
It is identified that Spatial Light Modulators (SLMs), digital optical devices that
modulate a light wavefront’s phase or amplitude across a two-dimensional surface,
are increasingly important as components in QPI techniques. To utilise an SLM
effectively it is necessary to characterise the modulation response of the device. A
novel application of ptychography in characterising an SLM is demonstrated,
generating a subpixel resolution of the display over the device’s entire active area.
Further developments are then explored in the integration of an SLM with
ptychography, with the ultimate aim of developing a new QPI technique with no
moving parts. The application of this technology is envisioned in high quality
quantitative phase videos.