1,721,469 research outputs found
The development of high power fibre chirped pulse amplification systems
No full textWith its broad gain bandwidth and high optical conversion efficiency, ytterbium (Yb)-doped silica fiber represents an attractive medium for the generation and amplification of ultrashort optical pulses. Research interest in Yb-doped fiber chirped pulse amplifier (CPA) systems first appeared in the late 1990s. However, the potential advantages and capabilities of Yb-doped fiber CPA systems were not fully studied during the early research. Further scaling of both the average power and the pulse energy have now become possible with the development of several key technologies that are associated with Yb-doped fiber CPA systems. Finally, the development of a novel fiber CPA system operating with strong selfphase-modulation (SPM) is described, which applied adaptive shaping of the spectral phase of the input pulses. The pre-compensation of both SPM induced phase distortion at high energies, and residual dispersion from mismatched stretcher/compressor technologies at low energies are investigated
Coherent control of wavefronts by planar photonic metasurfaces
No full textThe optical properties of materials can manifest differently in traveling and standing light waves. In standing waves, “coherent control” of the energy exchange between incident and scattered waves enables control of light with light without nonlinearity, at arbitrarily low intensity and on ultrashort (few optical cycle) timescales. This thesis reports on my research efforts towards application of coherent control techniques for shaping the wavefronts of light scattered by planar photonic metasurfaces: I show for the first time that the coherent control paradigm can be applied to optically thick and/or asymmetric sample/device structures, where previously only vanishingly thin (subwavelength thickness) structures were considered. I have derived the requisite illumination conditions for electric and magnetic field standing wave excitation of substrate-supported (e.g. at an air-glass substrate) meta surface structures; and numerically demonstrated applications to selective excitation spectroscopy and for thin film characterisation. I have introduced a new mechanism for active tuning of gradient index meta surfaces via coherent control of the phase gradient itself – turning what is conventionally a constant in the Generallized Snell’s law into a variable. This is demonstrated in the development of a meta surface design providing, through coherent selective excitation of Mie-type resonances in Si nano-pillars, coherently controlled beam steering (with no moving parts) over a continuous 9.1° range. I have also discussed its potential use for solid state Lidar
Continuous beam steering by coherent light-by-light control of dielectric metasurface phase gradient
No full textContinuous and reversible tuning of the properties of optical metasurfaces, as a functionality that would enable a range of device applications, has been a focus of the metasurface research field in recent years. Tuning mechanisms proposed and demonstrated so far have generally relied upon changing the morphology of a metasurface or the intrinsic properties of its constituent materials. Here we introduce, via numerical simulation, an alternative approach to achieve continuous tuning of gradient metasurface response, and illustrate its potential application to the challenge of continuous beam steering, as required for example in LIDAR and machine vision systems. It is based upon the coherent illumination of a silicon nano-pillar metasurface with two counter-propagating beams. Control of the input beams’ relative phase and intensity enables tuning of the individual nano-pillars’ electromagnetic response and thereby the phase gradient of the array, which in turn steers the direction of the output beam continuously over an angular range of approximately 9 degrees
Coherent absorption at interfaces for film thickness measurement and plasmonic selective excitation
No full textIn this oral presentation, we demonstrate using two coherent light beams to measure the thickness of absorptive thin films and selectively excite plasmonic resonances at the surface of transparent bulk substrates
Status and challenges in photocatalytic nanotechnology for cleaning air polluted with volatile organic compounds: visible light utilization and catalyst deactivation
No full textPhotocatalysis that utilizes semiconductor nanoparticles is one of the most investigated environmental nanotechnologies. It is a promising technology for air purification because it can decompose gaseous pollutants (particularly volatile organic compounds (VOCs)) directly into harmless CO2 and H2O under ambient conditions. Photocatalysis can be particularly suitable for removing low concentration pollutants (sub-ppm levels) in indoor environments where conventional adsorption technologies are not very efficient. Although photocatalytic air purification has been extensively investigated, it still falls far short of satisfying the requirements for practical usage. This review focuses on two main critical issues for improving the applicability of photocatalytic air purification: (1) increasing visible light activity to utilize ambient light and (2) preventing catalyst deactivation that hinders long-term usage of photocatalysts. Literature reports on the photocatalytic degradation of VOCs using visible light are surveyed and systematically categorized based on the type of photocatalytic materials and VOCs. Strategies taken to significantly increase the efficiency of visible light photocatalysts are introduced. On the other hand, photocatalyst deactivation processes are discussed according to the kinds of air pollutants, and various methods of assessing the extent of photocatalyst deactivation are outlined. The development of deactivation-resistant photocatalysts and their applications to air purification are also introduced and discussed. Finally, the status and the problems of the current research on photocatalytic air purification are critically discussed and suggestions for future studies of photocatalytic air purification are made.11Nsciescopu
Photocatalytic Air Purification Mimicking the Self-Cleaning Process of the Atmosphere
No full textPhotocatalytic air purification is a promising technology that mimics nature's photochemical process, but its practical applications are still limited despite considerable research efforts in recent decades. Here, we briefly discuss the progress and challenges associated with this technology.11Ysciescopu
Dataset for "Coherent illumination spectroscopy of nanostructures and thin films on thick substrates"
No full textData for the paper He, F., MacDonald, K., & Fang, X. (2018). Coherent illumination spectroscopy of nanostructures and thin films on thick substrates. Optics Express.
The paper has 5 figures in total, from Figure 1 to Figure 5.Only Figures 2(b), 3(b), 4(a), 4(b) and 5 have data. The data in each of these figures are recorded in a separate sheet in this dataset file.</span
Optical routing of nanospheres on plasmonic rails
No full textIn this oral presentation, we demonstrate plasmonic nanoparticle routers that can guide and route nanospheres in a microfluidic channel in response to incident light. The results suggest a new method for next-generation microfabrication and sensing
Nonlinear generation of THz vortex beams with tunable orbital angular momentum in si microdisks
No full textIn this poster presentation, we demonstrate waveguide-coupled microdisks that emit THz light with tunable orbital angular momentum. The topological charge of the THz light can be tuned by changing the driving infrared wavelengths in the difference-frequency generation process
Nanoparticle trapping and routing on plasmonic nanorails in a microfluidic channel
No full textPlasmonic nanostructures hold great promise for enabling advanced optical manipulation of nanoparticles in microfluidic channels, resulting from the generation of strong and controllable light focal points at the nanoscale. A primary remaining challenge in the current integration of plasmonics and microfluidics is to transport trapped nanoparticles along designated routes. Here we demonstrate through numerical simulation a plasmonic nanoparticle router that can trap and route a nanoparticle in a microfluidic channel with a continuous fluidic flow. The nanoparticle router contains a series of gold nanostrips on top of a continuous gold film. The nanostrips support both localised and propagating surface plasmons under light illumination, which underpin the trapping and routing functionalities. The nanoparticle guiding at a Y-branch junction is enabled by a small change of 50 nm in the wavelength of incident light
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