Discovering New Chiral Characterisation Techniques Within Second Harmonic Light Scattering

  • Ben Olohan

Student thesis: Doctoral ThesisPhD

Abstract

The linear chiroptical responses of molecules in solution often require large volumes (1mL) of a substance to distinguish one enantiomer from the other. Even then, they have circular dichroism on the order of millidegrees. Chiroptical harmonic scattering (CHS) is a new technique that shows promise to resolve enantiomers with much greater sensitivity. However, previous research in this field has focused either on chiroptical hyper-Rayleigh scattering in the second harmonic and third harmonic. Chiroptical hyper-Mie scattering has also been observed but is limited to the third harmonic. As such there are still areas that lack an effective scattering technique at the second harmonic, mostly concerning particles too large to undergo Rayleigh scattering. Additionally, second harmonic scattering has only been observed in plasmonic materials, raising questions regarding its general applicability, and there have been no observations for high index dielectric materials or semiconductors at the second harmonic. Furthermore, (CHS) reports have always been reported for very small spectral windows, which may not bewide enough to effectively resolve the chiroptical resonances.

Within the work contained in this thesis, we demonstrate chiroptical hyper-Tyndall scattering, first observed at the second harmonic wavelength. Moreover, we then show second harmonic hyper-Mie scattering for the first time using cadmium telluride helices. This completes the toolbox for second harmonic scattering effects for all particle sizes and demonstrates these effects in semiconductor materials. Furthermore, we show the ability of harmonic scattering as a characterisation technique by obtaining broad
circular dichroism spectra for gold and silver nanohelices, which we envision will lead to use of the technique across the whole spectrum.
Date of Award2 Oct 2024
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorVentsislav Valev (Supervisor) & Philip Shields (Supervisor)

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