104 research outputs found
Fabrication of crystalline Bragg reflectors for high power and integrated optical applications by multi-beam pulsed laser deposition
No full textTunable crystalline Bragg reflectors for high temperature, high power and integrated optical applications were fabricated via multi-beam Pulsed Laser Deposition. Apodised, p phase-shifted and >99% reflective quarter-wave structures are presented
Multi-beam pulsed laser deposition for engineered crystal films
No full textPulsed 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
PLD-grown Yb:Y<sub>2</sub>O<sub>3</sub> waveguide laser Q-switched by a graphene saturable absorber
No full textIn this paper, we present an Yb3+-doped Y2O3 waveguide laser fabricated by pulsed laser deposition (PLD) that is Q-switched using a mono-layer graphene saturable absorber
In Situ ocean observations: a brief history, present status and future directions
No full textObservations at and below the surface of the oceans are essential for understanding the ocean system and the role played by the ocean in earth’s climate, for documenting changes and for initialising, validating and improving ocean models. It is only since the late 20th century that, thanks to advances in microelectronics, battery technology and satellite communication in-situ observations, (together with satellite observations), have reached a volume and spatial distribution that allows us to track a wide range of global and regional phenomena. This review traces the development of in-situ ocean observations primarily from a physical standpoint and describes the internationally co-ordinated observing networks that now supply these observations. It considers the enormous changes that have occurred in the volume and distribution of these observations and the implication of these changes for defining the evolving state of the global ocean. Finally there is discussion of the prospects for further improving sustained ocean observations and for the delivery of integrated information from interrelated observing networks
Revisiting the seasonal cycle of the Timor throughflow: impacts of winds, waves and eddies
No full text© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Peña‐Molino, B., Sloyan, B., Nikurashin, M., Richet, O., & Wijffels, S. Revisiting the seasonal cycle of the Timor throughflow: impacts of winds, waves and eddies. Journal of Geophysical Research: Oceans, 127, (2022): e2021JC018133, https://doi.org/10.1029/2021jc018133.The tropical Pacific and Indian Oceans are connected via a complex system of currents known as the Indonesian Throughflow (ITF). More than 30% of the variability in the ITF is linked to the seasonal cycle, influenced by the Monsoon winds. Despite previous efforts, a detailed knowledge of the ITF response to the components of the seasonal forcing is still lacking. Here, we describe the seasonal cycle of the ITF based on new observations of velocity and properties in Timor Passage, satellite altimetry and a high-resolution regional model. These new observations reveal a complex mean and seasonally varying flow field. The amplitude of the seasonal cycle in volume transport is approximately 6 Sv. The timing of the seasonal cycle, with semi-annual maxima (minima) in May and December (February and September), is controlled by the flow below 600 m associated with semi-annual Kelvin waves. The transport of thermocline waters (<300 m) is less variable than the deep flow but larger in magnitude. This top layer is modulated remotely by cycles of divergence in the Banda Sea, and locally through Ekman transport, coastal upwelling, and non-linearities of the flow. The latter manifests through the formation of eddies that reduce the throughflow during the Southeast Monsoon, when is expected to be maximum. While the reduction in transport associated with the eddies is small, its impact on heat transport is large. These non-linear dynamics develop over small scales (<10 km), and without high enough resolution, both observations and models will fail to capture them adequately.B. Peña-Molino, B. M. Sloyan, M. Nikurashin, and O. Richet were supported by the Centre for Southern Hemisphere Oceans Research (CSHOR). CSHOR is a joint research Centre for Southern Hemisphere Ocean Research between QNLM and CSIRO. S. E. Wijffels was supported by the US National Science Foundation Grant No. OCE-1851333
The effect of relative plasma plume delay on the properties of complex oxide films grown by multi-laser multi-target combinatorial pulsed laser deposition
No full textWe report the effects of relative time delay of plasma plumes on thin garnet crystal films fabricated by dual-beam, combinatorial pulsed laser deposition. Relative plume delay was found to affect both the lattice constant and elemental composition of mixed Gd3Ga5O12 (GGG) and Gd3Sc2Ga5O12 (GSGG) films. Further analysis of the plasmas was undertaken using a Langmuir probe, which revealed that for relative plume delays shorter than ~200 µs, the second plume travels through a partial vacuum created by the first plume, leading to higher energy ion bombardment of the growing film. The resulting in-plane stresses are consistent with the transition to a higher value of lattice constant normal to the film plane that was observed around this delay value. At delays shorter than ~10 µs, plume propagation was found to overlap, leading to scattering of lighter ions from the plume and a change in stoichiometry of the resultant films
Finescale parameterizations of turbulent dissipation
No full textThis article (1) reviews and clarifies the basic physics underpinning finescale parameterizations of turbulent dissipation due to internal wave breaking and (2) provides advice on the implementation of the parameterizations in a way that is most consistent with the underlying physics, with due consideration given to common instrumental issues. Potential biases in the parameterization results are discussed in light of both (1) and (2), and illustrated with examples in the literature. The value of finescale parameterizations for studies of the large-scale ocean circulation in the presence of common biases is assessed. We conclude that the parameterizations can contribute significantly to the resolution of large-scale circulation problems associated with plausible ranges in the rates of turbulent dissipation and diapycnal mixing spanning an order of magnitude or more
Antarctic bottom and lower circumpolar deep water circulation in the eastern Indian Ocean
No full textAuthor Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 111 (2006): C02006, doi:10.1029/2005JC003011.Net northward transport below γn > 28.1 kgm−3 (≈3200 m) into the Perth Basin of between 4.4 and 5.8 Sv is estimated from a year-long current meter mooring array between the Broken and Naturaliste Plateaus. Northward transport of between 2.0 and 2.5 Sv of Antarctic Bottom Water (γn >28.2 kgm−3), that must upwell within the southern region of the Perth Basin, results in
an area-averaged diapycnal velocity and diffusivity of w*=2.5− 3.1× 10−6 ms−1 and κ = 13−15×10−4 m2s−1, respectively. Diffusivity estimates for the Perth Basin are several times larger than area averaged mixing estimates for the abyssal subtropical South Atlantic and Pacific Oceans. However, the dissipation of turbulent kinetic energy required to maintain the abyssal mixing in the Perth basin, ε=O(10−9 Wkg−1), is similar to that required in the South Atlantic Ocean. The area-averaged diffusivity in the Perth Basin does not require unreasonable energy dissipation rates as this ocean basin is only weakly stratified. The abyssal diffuvisity of the Perth Basin results from intense mixing at the basin boundary and in the basin interior over rough topography. The complex bathymetry and low abyssal stratification suggests that the Indian Ocean, for a given energy dissipation, may support a larger meridional overturning circulation than other subtropical basins.BMS was supported by funds from the Ocean and Climate
Change Institute at the Woods Hole Oceanographic Institution, and The James S. Cole
and Cecily C. Selby Endowed Fund and The Penzance Endowed Fund in support of Assistant
Scientists. The mooring array was funded by Australia’s CSIRO Marine Research
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