This paper reports a study of the effect of laser pulse repetition rate and substrate temperature on the properties of crystalline Sc2O3 films grown on <0001>-oriented sapphire via pulsed laser deposition (PLD). For the range of substrate laser-heating powers investigated, optimum <111>-film growth was obtained at the highest available repetition rate of 100 Hz. Scanning electron microscopy and X-ray diffraction measurements revealed that a decrease in the repetition rate favours highly textured/island growth. The repetition rate was also proven to affect the lattice constant of the films, with a difference up to 0.3% between the films grown at high and low repetition rates. The general trend indicates that the out-of-plane lattice constant of the film shifts closer to the bulk value when the pulse repetition rate is increased. However, the lattice constant could also be reduced through in-situ post-growth annealing, which had the additional benefit of reducing the width of the (222) rocking curve peak. This work provides further evidence that energetic-PLD dynamics leads to higher quality PLD-grown crystalline films and for this material undermines the old adage that lower pulse repetition rates lead to higher quality thin-film crystalline growth.

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Dielectric sesquioxide films (Sc 2 O 3 , Y 2 O 3 , and Lu 2 O 3 ) were fabricated by pulsedlaser deposition and tested in terms of their laser damage properties for pulses of 500 fs duration, at a wavelength of 1030 nm and at a 10 Hz repetition rate. Comparable tests were performed with magnetron-sputtered thin films of established optical-coating materials (SiO 2 , HfO 2 , and Nb 2 O 5 ), whose results served as a benchmark. The laser-induced damage thresholds of the sesquioxides are comparable to each other, and in the multi-pulse test regime show values close to ones of HfO 2 coatings. A lower damage threshold was observed for the polycrystalline Lu 2 O 3 film grown on sapphire compared to single-crystal Lu 2 O 3 grown on yttrium aluminium garnet (Y 3 Al 5 O 12 ), attributed to the highly textured morphology and potential for a greater density of defect states in these films. We conclude that pulsed-laser deposition is a potential fabrication method of sesquioxides for use in high-power resistant optical components for ultrashort-pulse lasers. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 International License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

This paper reports the fabrication and first demonstration of all-dielectric crystalline grating–waveguide reflectors comprising a Sc2O3 waveguide grown on a sub-wavelength-patterned sapphire substrate. Rigorous coupled-wave analysis is employed to simulate the operation of the structure, suggesting a 100% resonance reflectivity in theory. Structuring of the sapphire substrate is achieved using inductively coupled plasma etching, whilst pulsed laser deposition is used for epitaxial growth of the Sc2O3 crystalline waveguide. Devices with distinct TE- and TM-polarisation resonances around 1030-nm for an angle of incidence near 10° are demonstrated, with reflectance approaching 90%. The discrepancy in reflectivity is attributed to the waveguide thickness variation and surface roughness. Refinement of the fabrication processes and tolerances should lead to improvement in the surface quality of the crystalline grating–waveguide structure and operation closer to the ideal resonance reflectivity.