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The effects related to diffraction and interference are ubiquitous in phenomena involving electromagnetic wave propagation, and are accurately predicted and described within the framework of classical electrodynamics. In the vast majority of the cases the qualitative features of the evolution of a propagating wave can be inferred even without detailed calculations. A field distribution will spread upon propagation, will accumulate phase along the direction of power flow, will exert mechanical forces upon scattering objects in the direction of propagation etc. When such predictions fail, counterintuitive effects and new functionalities can be engineered. In this work a series of exceptional cases under different degrees of field confinement have been isolated. In such instances the electromagnetic behavior significantly deviates from conventional cases. In particular, considering structures with monodimensional field confinement, the only possible class of diffraction free surface waves has been introduced. Again within the context of surface waves the mechanism of Enhanced Evanescent Tunneling (EET) has been proposed, which allows a net power flow to be sustained by evanescent fields only with applications to subdiffraction imaging. Increasing the degree of field confinement, a unique class of fully dielectric waveguide arrays able to support negative effective index modes has been theoretically demonstrated. Finally the opto-mechanical consequences of such effective negative index environments have been studied, highlighting counterintuitive properties. Instrumental to these findings was the introduction of a general theory of optical forces in terms of vector spherical harmonics.

Effects of binding on the electromagnetic structure of a nucleon in a nucleus is examined for the two-pion part of the nucleon form factor. The nucleon is assumed to be bound in a harmonic oscillator potential and also coupled to the pion field through the Chew-Low type interaction. In the tight-binding limit, the nucleon structure approaches that given in the static Chew-Low theory, as expected, while the loose-binding limit gives the free nucleon case with nucleon recoil corrections. Implications of this binding on the magnetic moments of the tri-nucleon systems are investigated, and it is found that for a realistic strength of the harmonic oscillator potential the binding effect is too small to be very significant. Effects of the Pauli Principle are also discussed. / Thesis / Master of Science (MSc)

<p> A measurement of the cross section for the interaction of electromagnetic radiation with matter has been undertaken. Total cross sections for 29 photon energies from 121 keV to 10.8 MeV in 9 target elements from carbon to uranium have been realized and pair production cross sections, for energies above 2 MeV, deduced from the results. A direct measurement of the partial pair cross section for photons with energies from 1120 to 2754 keV in 6 target elements from titanium to lead has also been included.</p> / Thesis / Doctor of Philosophy (PhD)

Thesis advisor: Krzysztof Kempa / “Simulations are like an experiment but on a computer.” – K. Kempa. Powerful ideas can be explored in immense detail and unmatched flexibility through computational resources. Combined with the beauty of electromagnetics, worlds of situations and problems can be uncovered. Of the many interesting phenomena available to study, a relatively recent explosion of engineered plasmonic materials has benefitted greatly from numerical breakthroughs in simulating Maxwell’s equations. Using these tools on novel metamaterial systems, composite materials with precisely designed structural features, the analysis and optimization probes the unique capabilities they have interacting with light. Example phenomena from this work includes fundamental principle breaking, extraordinary optical transmission, negative refraction, and superconductivity enhancement. The systems that harbor such outstanding feats fall into the umbrella term of metamaterials, each with distinct geometry and contrasting electrical properties that allow for an engineered control of the effective structural dielectric function. As the response to electromagnetic radiation, manipulating the dielectric function is key to creating and discovering the effects that control light, without changing any chemistry. This work scales pedagogically through the different types of metamaterials, beginning first with 2D planar checkerboard structures with highly non-linear percolation. In combination with spoofed plasmonics, the longstanding symmetry of the Babinet principle is challenged. Layers of checkerboards are then stacked and translated to create subwavelength gaps for which plasmonic coupling between layers aids in optical transmission. In fact, there is similar physics controlling other layered quasi-complementary structures shown by comparison to experimental transmittance data. A further stage introduces photonic crystals constructed out of 3D periodic lattice of nanoparticles. Photonic band structure calculations for properly designed systems suggest the possibility of bandwidths of the IR spectrum where the crystal has a negative refractive index. Such a material property allows for the invention of lenses that beat the diffraction limit, applicable to subwavelength imaging. Lastly, non-local extensions to plasmonics are theoretically worked into expressions for superconductivity, creating a resonant anti-shielding effect, in composite topological crystal/superconductor layered arrangements. Applying this to known topics, like Bi2Se3 and MgB2, shows significant boost to electron pairing and thus rises in superconducting critical temperature. Central to all the systems and effects explored are the modifications made to the dielectric function of each effective medium. Supported by electromagnetic simulations and theoretical efforts, the listed engineered materials transform the dielectric environment purposefully to originate the mentioned exotic optical phenomena. / Thesis (PhD) — Boston College, 2023. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

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