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Sandy Mathew presents

 Enhancement of the second-order nonlinear optical response of hybrid plasmonic nanostructures

Wednesday, December 20th 2023 at 14:00

Room D420 – Institut Néel

The defence will be in English.


Abstract: An ideal all photonic integrated circuit (IC) requires components that perform amplification, signal processing, logic gate operations and several equivalent functions of an electronic IC packed in to a space of few millimeters. To achieve such a feat, use of different materials adapted to different functions is inevitable. Among them, nonlinear optical materials are crucial as a potential source of single or twin-photons. However, when reducing size of a nonlinear material to nanoscale, enhancing the excitation and emission through resonant interactions becomes a prerequisite to balance the drop in nonlinear efficiency due to volume reduction. In this study, by combining nanofabrication of plasmonic and nonlinear (hybrid) structures, a versatile experimental setup and quantitative numerical simulation of both second harmonic generation (SHG) and spontaneous parametric down conversion (SPDC) second order processes, a comprehensive understanding of these nonlinear interactions and their efficiency in our systems is possible. One of the primary objectives of this work, therefore, consists in studying the origin of SHG from gold nanostructures in order to identify the dominant nonlinear source. It allows to shed some light on and discriminate between incompatible conclusions presented in the literature.We report that, of the three main nonlinear sources invoked in the literature, namely, parallel and normal surface source and non-local bulk source, non-local bulk and parallel surface source dominates the response while normal surface was found to be negligible contrary to most literature. A second objective of this thesis work was to achieve experimentally observable SPDC photon pair emission rate using hybrid structures which has not been possible to date. While optimising the plasmonic nanoantennas theoretically improves the photon pair rate due to resonant interaction, combining it with a material of better nonlinearity such as gallium phosphide (GaP) increases the rate to an order of magnitude higher than before. The nanowire form of GaP and the structural variations of this material, as a result, leads us to develop an experimental protocol of hybrid structure fabrication based on their distinctive SHG responses. Thus, it opens up novel possibilities for integrated nanoscale photon pair sources.