Multi-beam pulsed laser deposition for engineered crystal films

Abstract

Pulsed laser deposition (PLD) is a quick, versatile technique for crystal film growth. Multi-beam PLD extends the basic PLD setup to include multiple lasers and targets, and has shown immense promise for the engineering of custom crystal films and structures. The full potential of the technique has not, however, yet been fully explored. The experiments in this thesis have been designed to investigate, extend and improve multibeam PLD, to provide new avenues for fabrication of sophisticated designer films and to find applications that truly exploit the technique's potential.

The effect of relative delay between plasma plumes on crystal properties was investigated and was found to influence lattice constant for delay values of <400 µs due to higher energy ion bombardment of the growing film. The shutter technique for multibeam crystal engineering was developed and demonstrated via the automated growth of garnet mixed films, superlattices and chirped structures. The method was used to grow crystalline garnet Bragg reflectors with a range of designs, including pi-phase shifted and quarter-wave stacks with up to 145 layers and 99% peak reflectivity. A Gaussian profile, grating-strength apodised Bragg stack was grown, with the resulting reduction in side band reflections observed as expected. This represents the first known example of such sophisticated crystal engineering by PLD. Routes to using single- and multi-beam PLD for rapid prototyping of laser crystals were also explored. Double-clad crystalline channel waveguides were fabricated via physical micromachining of PLD-grown garnet multilayer films and subsequent overgrowth. Millimetre-sized crystalline features were grown via single-beam PLD through shadow masks and funnels, culminating in fabrication of a hybrid garnet crystal by a combination of multi-beam PLD and plume funnelling.

The results in this thesis represent steps towards the true exploitation of PLD, but much is still to be done. Many routes for future improvement have been suggested, building on the novel techniques developed for this thesis, including the growth of sesquioxides as component layers of functional Bragg stacks capable of withstanding high powers and temperatures.

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Identifiers

ORCID for Robert Eason: orcid.org/0000-0001-9704-2204

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