Public defence in Radio Engineering, M.Sc. Reza Heydarian

The title of the thesis: Diffraction of hollow beams by dielectric microparticles and microsphere assisted microscopy

Doctoral student: Reza Heydarian
Opponent: Prof. Ivan Kassamakov, University of Helsinki, Finland
Custos: Prof. Constantin Simovski, Aalto University School of Electrical Engineering, Department of Electronics and Nanoengineering

Hollow beams are light beams with zero intensity on the beam axis. While the scattering and diffraction of light by the spherical and cylindrical particles represent well-established areas, the diffraction of hollow (tubular in 3D and cosine in 2D) wave beams in the visible light range by microspheres and microcylinders has been weakly studied. One of the key findings in this study is the appearance of a dark spot outside the particle, which is distanced from the interface by order of a wavelength. Another feature that makes this dark spot unique is that, despite its distance from the particle’s interface, evanescent waves are the major contributor to forming it. This discovery would be most interesting for physicists developing optical traps, especially particle waveguides for quantum computing. 

The second part of this work addresses a long-standing problem of label-free microscopy. An unavoidable barrier for any traditional imaging system is diffraction limit, which means, the resolution cannot go beyond half of the operating wavelength due to the loss of evanescent waves during wave propagation. The capability of a microsphere to break this barrier and achieve super-resolution has been revealed experimentally a decade ago, and a reliable theoretical explanation is yet to be found. In our new theory, the polarization of the sources plays a crucial role. A dipole does not radiate along its axis. Radially polarized sources will produce hollow beams after their interaction with the microspheres, which makes the information about their location retrievable. This is a rather general mechanism that does not require any resonant properties of the microsphere or object.

Thesis available for public display 10 days prior to the defence at: https://aaltodoc.aalto.fi/doc_public/eonly/riiputus/

Contact information:

Doctoral theses in the School of Electrical Engineering: https://aaltodoc.aalto.fi/handle/123456789/53