| Author: | Gao, Han |
| Title: | Plasmonic gold nanohelicoid mediated chiral light-matter interaction |
| Advisors: | Jin, Wei (EEE) Lei, Dangyuan (AP) |
| Degree: | Ph.D. |
| Year: | 2022 |
| Subject: | Nanophotonics Chirality Nanoparticles Plasmonics Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Electrical Engineering |
| Pages: | xviii, 113 pages : color illustrations |
| Language: | English |
| Abstract: | Chiral light-matter interaction attracts significant interests in classical and quantum optics due to its underlying applications in quantum communication, all-optical selection and separation, and biosensing, etc. Chiral plasmonic nanostructures can uniquely and controllably enhance the chiral light-matter interaction effectively at the nanoscale. Top-down lithography techniques are applied to fabricate plasmonic chiral nanostructures with two-dimensional geometries, and it has remained challenging to prepare three-dimensional nanostructures. Recently, a bottom-up wet-chemistry strategy has been developed for synthesizing nanoparticles with innate chirality. Chiral gold nanohelicoids (GNHs) with intense chiroptical activity are synthesized in the presence of chiral amino acids/ peptides. These GNHs with intrinsic chiral structures open a new pathway for building up nanophotonic systems with single chiral nanostructures. To unleash the great potential in nanophotonics, it is important to unravel the underlying mechanism responsible for the interaction between chiral light and these GNHs. This thesis reports the GNH-mediated chiral light-matter interaction by investigating the interaction between the GNHs and chiral light, an achiral photonic microcavity, and chiral molecules. Firstly, I present a thorough study on the chiral excitation and emission properties of GNHs at the single-particle level to deeply understand the chiroptical properties of the GNHs. The photoluminescence (PL) of a single GNH under circular light excitation is also circularly polarized, and the polarization-resolved PL spectroscopy of chiral PL signals have a preferential handedness to the excitation polarization. Two physical models are developed to understand these experimental observations. Based on the understanding of the GNH’s chiral absorption and emission properties, I subsequently investigate the effect of electromagnetic coupling between the GNH and an achiral photonic microcavity in the chiral Purcell enhancement of the hybrid system. The present of the GNH on the SiO2/Si FP cavity introduces an additional phase change at their interface, leading to compound peaks spectrally detuned from the original FP modes. Importantly, the introduced GNHs on the SiO2/Si substrate could modulate the Si Raman signals in a chiral manner, demonstrating the effectiveness of chiral modulation in the local near-field regime. Finally, to extend the chiral light-matter interaction of the GNH with chiral active materials, and further explore the feasibility of GNHs in practical applications, I combine the GNHs with chiral molecules for enantioselective recognition by Raman spectroscopy. In the presence of GNHs, I observe a significant difference in the Raman scattering signal intensities of two enantiomers probably due to surface-enhanced chiral Raman scattering. In summary, the chiral excitation and emission characteristics of the GNH reveals the relationship between the handedness of chiral emitters and incident circular polarization states. Chiral scatterometry and Raman scattering of the GNH-FP hybrid cavity extends the coupling of localized surface plasmon resonances and FP modes to the chiral regime with an enhanced chiroptical effect. Pairing the use of GNHs with chiral molecules’ recognition through Raman spectroscopy reports underlying applications of the GNHs in chirality-based biosensing and probing. Those works on plasmonic GNHs provide comprehensive insights of chiral light-matter interaction mechanisms of chiral plasmonic nanostructures, and thus flourish their applications in chiral imaging, photonic circuits, and enantio-discrimination. |
| Rights: | All rights reserved |
| Access: | open access |
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