Pulsed laser deposition of thin-film oxides for waveguide lasers

Abstract

Pulsed laser deposition (PLD) is a technique for depositing materials and PLD displays versatility and high growth rates. It can be used to grow active single-crystal materials, which can be used as planar waveguide lasers. During PLD, particulates can be embedded into the growing film, which can reduce the planar waveguide lasers optical-to-optical efficiency and degrade the physical characteristics of a grown film. The experiments presented in this thesis focus on reducing the density of particulates in PLD-grown films and using this knowledge to grow high quality, novel materials.Three particulate reduction techniques were investigated including a shadow-mask, segmented targets and bi-directional ablation. All of these techniques reduced the particulate density and bi-directional ablation was implemented as the new standard ablation regime. This novel technique increased target utilisation by 50%, target lifetime by 100% and demonstrated an average particulate density reduction of 80%. As a direct result of bi-directional ablation, films with losses down to 0.12 dB/cm were realised.
The versatility of PLD was exploited to tune the lattice constant of a mixed-sesquioxide film to demonstrate a <0.1% lattice mismatch with sapphire. Waveguiding was realised for the first time in a 3% Yb-doped sapphire waveguide, a material that is impossible to grow via traditional crystal growth methods.
A Yb:LuAG laser with cladding layers was demonstrated, for the first time with PLD, with output powers of 3.3 W. Using bi-directional ablation, an Er:YGG film was grown and 3.46 dB of gain was realised in a channel waveguide geometry. Previous attempts had not achieved any such gain due to high losses.The particulate reduction technique demonstrated in this thesis and the subsequent exploitation, pave the way for PLD as a commercially viable technique for waveguide fabrication. Without the drawback of high particulate densities, high quality optical devices can be fabricated via PLD that would compete with other growth techniques.

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Identifiers

ORCID for Jacob Mackenzie: orcid.org/0000-0002-3355-6051

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