Public Defense: Mahdieh Gholamimayani

 Mahdieh Gholamimayani is defending her thesis High-Resolution Fourier Ptychographic Microscopic Imaging with Polarization Diversity for the degree philosophiae doctor (PhD) at the University of South-Eastern Norway
 

The doctoral work has been carried out at the Faculty of Technology, Natural Sciences and Maritime Sciences following the PhD programme in Applied Micro- and Nanosystems.

• Download the thesis 

You are welcome to follow the digital trial lecture and public defence.

• Join virtually (Zoom)

Summary

A high-resolution imaging microscope is required to monitor and identify fine details of biological samples, and live cells. Several limitations of conventional microscopy has motivated researchers to develop computational schemes, such as Fourier ptychographic microscopy (FPM). These limitations may include phase loss, narrow depth-of-field, aberrations, balancing spatial resolution with field-of-view, and finite space bandwidth. To defeat these compromises, a high numerical aperture (NA) objective lens can be used with a small field of view (FoV) and then it can mechanically scan the sample region of interest. The captured images are then stitched together, and a high-resolution image with a large FoV can be achieved. Nevertheless, this method suffers from long data acquisition time with precise and expensive scanning translational stages.

Fourier ptychography microscopic imaging utilizes a low NA objective lens with its inherent wide FoV and increases the bandwidth of the spatial frequencies with angularly-varied illumination. This provides a high-resolution image while maintaining a large FoV. The applied phase retrieval techniques help the recovery of the phase informational well as a long working distance and an extended depth of field (DoF) is obtained. Regarding resolution enhancement, coherent aperture synthesis and structured illumination can be contrasted with FPM. The reconstruction methodology employed by FPM differs from synthetic aperture approaches in its utilization of nonlinear optimization algorithms, akin to translational diversity techniques and ptychography methods.

In this thesis, the vectorial nature of the light in the form of polarization sensitivity has been applied to the FPM. This polarization-sensitive FPM, namely pFPM provides quantitative absorption and phase information for complex and birefringent specimens without mechanical movements of optical components. Utilizing a semispherical LED illumination array with an achieved resolution of 244 nm, this method can produce a high synthetic NA.

Another experimental setup has been proposed in this thesis, with a focus on FPM with a higher refractive index waveguide medium than free space. This configuration can extend the illumination NA beyond unity, which is not possible in the standard free-space propagation FPM setups. The obtained resolution is 130 nm, breaking the highest FPM resolution so far.

In addition to the studies mentioned above, Fourier ptychographic microscopy is employed for the accurate identification and characterization of surface flaws on glass. Utilizing the reconstructed quantitative phase map, we successfully measured various flaw properties, including length, width, depth, eccentricity, and orientation. Validation through Atomic Force Microscopy confirmed the precision of our measurements. Statistical analyses revealed an uneven spatial distribution of flaws, challenging conventional strength prediction models. This method can be promising for advancing transparent material studies and finding practical applications in in-line production testing for glass.