How do adult beginning Spanish students perceive their teacher\u27s written feedback on their compositions?

Most of the literature on written feedback to date has attended to feedback techniques and the effects of such approaches on students\u27 writing skills. Little emphasis has been placed on students\u27 perspectives on teachers\u27 written feedback. For this reason, the present study investigated how adult beginning students react to their teacher\u27s written feedback on their Spanish compositions. The study used qualitative methods of data collection---questionnaires for the students, interviews with teachers and students and participant observations---in order to explore their reactions and perceptions. The findings show that the general positive reaction students had in relation to their teacher\u27s written feedback was influenced by different factors such as the techniques their teachers used and the acceptance of their teacher\u27s authority. An analysis of the findings was conducted through the perspective of writing-as-process, which showed that the stages of the process---planning, drafting, revising and proofreading (Gardner, 1996)---were not treated with equal emphasis. Specifically, issues related to content and organization were largely overlooked in favor of grammatical corrections. Implications of these findings are also discussed

Optical Metasurfaces with Advanced Phase Control Functionalities

The development of a metasurface platform with advanced micro- and nano-fabrication techniques has attracted a lot of attention. It exhibits a broad range of applications in the lens, hologram, image processing, vortex beam generation, information encoding, sensing, etc. Metasurfaces are ultrathin planar nanostructures made of subwavelength metallic or dielectric elements that can efficiently control the light characteristics such as polarisation, dispersion, amplitude, and phase. The high-index dielectric metasurfaces exhibit low loss and produce various types of resonant effects such as Mie-type resonances, Huygens' resonances, and so on. The Huygens' resonant regime of the dielectric metasurfaces exhibits the near-unity transmission window with a 2pi-phase coverage. The efficient 2pi-phase control capability with high transmittance feature makes the metasurfaces versatile tools for wavefront manipulation. The challenge is to realize the practical application of the metadevices such as beam deflection, optical image processing, sensing, hologram, lens, and so on. The performance of such metadevices can be made highly efficient by incorporating carefully engineered phase discretisation. Due to such engineered subwavelength wave discretisation, new functionalities that are not possible to date can be achieved by governing the phase response. In this thesis, I will first demonstrate the efficient control of deflection angle with high diffraction efficiency in the visible wavelength. I will also discuss deeply subwavelength metasurface resonators for terahertz wavefront manipulation. Then, I will focus on a novel dielectric resonant metagrating-based highly sensitive optical biosensing technique. Finally, I will demonstrate Mie-resonant dielectric metasurfaces can be used as a passive filter to perform image processing in the form of edge detection of a target object

High-Efficiency Visible Light Manipulation Using Dielectric Metasurfaces

The development of a miniaturised device that provides efficient beam manipulation with high transmittance is extremely desirable for the broad range of applications including holography, metalens, and imaging. Recently, the potential of dielectric metasurfaces has been unleashed to efficiently manipulate the beam with full 2 pi-phase control by overlapping the electric and magnetic dipole resonances. However, in the visible range for available materials, it comes with the price of higher absorption that reduces efficiency. Here, we have considered dielectric amorphous silicon (a-Si) nanodisk and engineered them in such a way which provides minimal absorption loss in the visible range. We have experimentally demonstrated meta-deflector with high transmittance which operates in the visible wavelengths. The supercell of proposed meta-deflector consists of 15 amorphous silicon nanodisks numerically shows the transmission efficiency of 95% and deflection efficiency of 95% at operating wavelength of 715 nm. However, experimentally measured transmission and deflection efficiencies are 83% and 71%, respectively, having the experimental deflection angle of 8.40 degrees. Nevertheless, by reducing the supercell length, the deflection angle can be controlled, and the value 15.50 degrees was experimentally achieved using eight disks supercell. Our results suggest a new way to realise the highly transmittance metadevice with full 2 pi-phase control operating with the visible light which could be applicable in the imaging, metalens, holography, and display applications

Hybrid Metasurface Based Tunable Near-Perfect Absorber and Plasmonic Sensor

We propose a hybrid metasurface-based perfect absorber which shows the near-unity absorbance and facilities to work as a refractive index sensor. We have used the gold mirror to prevent the transmission and used the amorphous silicon (a-Si) nanodisk arrays on top of the gold mirror which helps to excite the surface plasmon by scattering light through it at the normal incident. We numerically investigated the guiding performance. The proposed absorber is polarization independent and shows a maximum absorption of 99.8% at a 932 nm wavelength in the air medium. Considering the real applications, by varying the environments refractive indices from 1.33 to 1.41, the proposed absorber can maintain absorption at more than 99.7%, with a red shift of the resonant wavelength. Due to impedance matching of the electric and magnetic dipoles, the proposed absorber shows near-unity absorbance over the refractive indices range of 1.33 to 1.41, with a zero-reflectance property at a certain wavelength. This feature could be utilized as a plasmonic sensor in detecting the refractive index of the surrounding medium. The proposed plasmonic sensor shows an average sensitivity of 325 nm/RIU and a maximum sensitivity of 350 nm/RIU over the sensing range of 1.33 to 1.41. The proposed metadevice possesses potential applications in solar photovoltaic and photodetectors, as well as in organic and bio-chemical detection.The authors acknowledge the funding support provided by the Australian Research Council (ARC). M.R. sincerely appreciates funding from ARC Discover Early Career Research Fellowship (DE170100250)

Dual-polarized highly sensitive plasmonic sensor in the visible to near-IR spectrum

We propose and numerically characterize the optical characteristics of a novel photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensor in the visible to near infrared (500–2000 nm) region for refractive index (RI) sensing. The finite element method (FEM) is used to design and study the influence of different geometric parameters on the sensing performance of the sensor. The chemically stable plasmonic material gold (Au) is used to produce excitation between the core and plasmonic mode. On a pure silica (SiO2) substrate, a rectangular structured core is used to facilitate the coupling strength between the core and the surface plasmon polariton (SPP) mode and thus improves the sensing performance. By tuning the geometric parameters, simulation results show a maximum wavelength sensitivity of 58000 nm/RIU (Refractive Index Unit) for the x polarization and 62000 nm/RIU for the y polarization for analyte refractive indices ranging from 1.33 to 1.43. Moreover, we characterize the amplitude sensitivity of the sensor that shows a maximum sensitivity of 1415 RIU−1 and 1293 RIU−1 for the x and y polarizations, respectively. To our knowledge, this is the highest sensitivity for an SPR in published literature, and facilitates future development of sensors for accurate and precise analyte measurement. The sensor also attains a maximum figure of merit (FOM) of 1140 and fine RI resolution of 1.6 × 10−6. Owing to strong coupling strength, high sensitivity, high FOM and improved sensing resolution, the proposed sensor is suited for real-time, inexpensive and accurate detection of biomedical and biological analytes, biomolecules, and organic chemicals.This work is supported by Australian Research Council (grant no. DP170104984). We gratefully acknowledge their support

High Fluence Chromium and Tungsten Bowtie Nano-antennas

Nano-antennas are replicas of antennas that operate at radio-frequencies, but with considerably smaller dimensions when compared with their radio frequency counterparts. Noble metals based nano-antennas have the ability to enhance photoinduced phenomena such as localized electric fields, therefore-they have been used in various applications ranging from optical sensing and imaging to performance improvement of solar cells. However, such nano-structures can be damaged in high power applications such as heat resisted magnetic recording, solar thermo-photovoltaics and nano-scale heat transfer systems. Having a small footprint, nano-antennas cannot handle high fluences (energy density per unit area) and are subject to being damaged at adequately high power (some antennas can handle just a few milliwatts). In addition, given that nano-antennas are passive devices driven by external light sources, the potential damage of the antennas limits their use with high power lasers: this liability can be overcome by employing materials with high melting points such as chromium (Cr) and tungsten (W). In this article, we fabricate chromium and tungsten nano-antennas and demonstrate that they can handle 110 and 300 times higher fluence than that of gold (Au) counterpart, while the electric field enhancement is not significantly reduced.Te authors gratefully acknowledge the fabrication facilities provided by Australian National Fabrication Facility (ANFF ACT node, Australia). We would acknowledge the fnancial support from UNSW Canberra, Australia. We also would like to thank Te Asian Ofce of Aerospace Research and Development (AOARD US Air Force FA2386-15-1-4084), Australian Research Council (ARC LP160100253, DP170103778 and DE190100413) to provide the funding

Modelling and simulation of surface plasmonic resonance in photonic crystal fiber / Rifat Ahmmed Aoni

Surface Plasmon Resonance (SPR) refers to the coupling between the electromagnetic wave and the surface plasmonic wave (SPW) on the surface between a metal and a dielectric medium. Since last decade, the SPR behavior is widely applied in prism based SPR sensor, which is bulky and not suitable for remote monitoring applications. To overcome this limitation, photonic crystal fiber (PCF) based SPR sensor had attained great attention with the advantages of easily launching light through the fiber, small-size and design flexibility. To establish the SPR phenomena, metal deposition is necessary. Nowadays, in most of the PCF-SPR sensors, metal is selectively deposited inside the airholes with numerous selective metallic and liquid channels, which made fabrication of such sensors impractical or very challenging. In this dissertation, four different PCF-SPR sensors are introduced with relatively high or comparable sensing performance. The proposed sensors are numerically investigated using the commercial Multiphysics COMSOL software. First study presents the PCFSPR sensor with only one graphene-silver deposited channel and two high refractive index (RI) liquid channels. It shows the amplitude sensitivity as high as 418 RIU-1 and the wavelength interrogation sensitivity of 3000 nm/RIU. In the second study, focusing on the metal deposition problem, a flat structure PCF-SPR sensor is developed where, the metal layer is deposited outside the fiber structure and the sensor will perform the external sensing scheme to detect the analytes. The proposed flat SPR sensor enhances the evanescent field resulting the amplitude sensitivity as high as 820 RIU-1 and the remarkable wavelength interrogation sensitivity of 23,000 nm/RIU. In the third study, a practically simple PCF SPR sensor is proposed. The metallic layer and sensing layer are placed outside the fiber structure which makes the sensor configuration simple and the analyte detection process easier. The proposed sensor shows the amplitude and wavelength interrogation sensitivity of 320 RIU-1 and 4000 nm/RIU, respectively. In the last work, copper is utilized in PCF SPR sensor for the first time due to its long-term stable sensing performance; and graphene is used to prevent copper oxidation and enhance the sensor performance. Similar to the third design, here the metallic layer and sensing layer are positioned outside the fiber structure resulting easy detection mechanism. It shows the wavelength interrogation sensitivity of 2000 nm/RIU with the sensor resolution of 5×10-5 RIU. Due to the promising sensitivity, the proposed sensors would be potential candidates for chemical, bio-chemical, organic chemical and organic molecule analytes detection with realizable structure