Laser machining of strain defects to control excitons in cuprous oxide

Gavin-Pitt, Samuel 2025. Laser machining of strain defects to control excitons in cuprous oxide. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

The purpose of this project was to investigate the feasibility of infrared picosecond laser machining of cuprous oxide (Cu2O) by two-photon absorption and to determine the effects that this has on its optical properties, specifically those of its excitons. Machining was achieved for pulse energies exceeding 0.4 μJ for mid-sampleonly machining, and 0.2 μJ for machining on the surface. The latter was invariably found to occur much more readily than the former. SEM images of the damage revealed evidence of laser filamentation due to nonlinear selffocusing which is known to result in multi-photon absorption - the absorption mechanism for laser machining. The filament-like damage extended through to depths within the samples on the scale of 10s of μm and demonstrated widths as low as 30 nm. SEM images of the surface effects of laser machining show apparent sample melting which is consistent with the energy of the laser pulses given the volume of melted material. Shifts in the exciton absorption peaks (on the scale of 10s of μeV), and the introduction of birefringence in the crystal both occurred anisotropically in the material surrounding the machinings suggesting the presence of an asymmetric strain field caused by the damage. The phase difference induced by birefringence was indicative of a shift in the refractive index of the material of up to about Δn = 2×10−3. Raman spectrometry revealed an increase in the presence of split copper vacancies (or Cu3O2) in the material surrounding the damage as evidenced by changes in the Raman activity and photoluminescence. The damage absorbed light for a broad range of frequencies, though transmission imaging of the machinings showed that the most significant change in transmission was not this absorption and was attributed to variations in n surrounding the damage or increased scattering due to surface damage.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Physics and Astronomy
Subjects:	Q Science > QC Physics
Uncontrolled Keywords:	Rydberg excitons, laser machining, semiconductor physics, cuprous oxide, nonlinear optics, quantum optics, condensed matter physics, exciton strain traps, orthoexcitons, transmission spectroscopy, Raman spectroscopy, differential interference contrast
Funders:	College Funded
Date of First Compliant Deposit:	18 August 2025
Last Modified:	18 Aug 2025 14:14
URI:	https://orca.cardiff.ac.uk/id/eprint/180474

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