Determining the Phase and Amplitude Distortion of a Wavefront using a Plenoptic Sensor

We have designed a plenoptic sensor to retrieve phase and amplitude changes resulting from a laser beam's propagation through atmospheric turbulence. Compared with the commonly restricted domain of (-pi, pi) in phase reconstruction by interferometers, the reconstructed phase obtained by the plenoptic sensors can be continuous up to a multiple of 2pi. When compared with conventional Shack-Hartmann sensors, ambiguities caused by interference or low intensity, such as branch points and branch cuts, are less likely to happen and can be adaptively avoided by our reconstruction algorithm. In the design of our plenoptic sensor, we modified the fundamental structure of a light field camera into a mini Keplerian telescope array by accurately cascading the back focal plane of its object lens with a microlens array's front focal plane and matching the numerical aperture of both components. Unlike light field cameras designed for incoherent imaging purposes, our plenoptic sensor operates on the complex amplitude of the incident beam and distributes it into a matrix of images that are simpler and less subject to interference than a global image of the beam. Then, with the proposed reconstruction algorithms, the plenoptic sensor is able to reconstruct the wavefront and a phase screen at an appropriate depth in the field that causes the equivalent distortion on the beam. The reconstructed results can be used to guide adaptive optics systems in directing beam propagation through atmospheric turbulence. In this paper we will show the theoretical analysis and experimental results obtained with the plenoptic sensor and its reconstruction algorithms.Comment: This article has been accepted by JOSA

Characterizing Atmospheric Turbulence with Conventional and Plenoptic approaches

Atmospheric turbulence is a phenomenon of interest in many scientific fields. The direct effects of atmospheric turbulence can be observed in everyday situations. The twinkling of stars is an indicator of weak atmospheric turbulence while the shimmering of objects above a hot surface is an indicator of strong atmospheric turbulence. The effects of atmospheric turbulence are generally considered a nuisance to optical applications. Image blurring effects are often present when observing distant objects through atmospheric turbulence. Applications that require maintaining the coherence of a laser beam, such as in free space optical communication, suffer from poor link quality in the presence of atmospheric turbulence. Attempts to compensate for the effects of atmospheric turbulence have varied in effectiveness. In astronomical applications, weak cases of atmospheric turbulence have been successfully compensated with the use of a Shack-Hartmann wavefront sensor combined with adaptive optics. Software techniques such as “Lucky Imaging” can be useful when clear images briefly appear through the presence of weak turbulence. However, stronger cases of atmospheric turbulence often found in horizontal or slant paths near the Earth’s surface present a much more challenging situation to counteract. This thesis focuses primarily on the effects of strong or “deep” atmospheric turbulence. The process of compensating for the effects of strong atmospheric turbulence begins with being able to characterize it effectively. A scintillometer measures the scintillation in the intensity of a light source to determine the strength of current turbulence conditions. Thermal fluctuation measurements can also be used to derive the strength of atmospheric turbulence. Experimental results are presented of a developed large aperture scintillometer, thermal probe atmospheric characterization device, and a transmissometer. While these tools are effective in characterizing atmospheric turbulence, they do not provide for a means to correct for turbulence effects. To compensate for the effects of atmospheric turbulence, the development of the Plenoptic Sensor is presented as a wavefront sensor capable of handling strong turbulence conditions. Theoretical and experimental results are presented to demonstrate the performance of the Plenoptic Sensor, specifically in how it leads to adaptive optics algorithms that can rapidly correct for the effects of turbulence

The Study Of Chinese Trade Ceramics In Sungai Sadong, Sarawak

Tesis ini membincang tentang hasil kajian seramik perdagangan dari China yang ditemui di Senangeh, Benat Hilir and Gedong di Sungai Sadong, Sarawak. Metodologi kajian yang diguna terdiri dari analisis secara morfologi dan saintifik serta kajian perbandingan untuk menjawab isu and persoalan tentang klasifikasi seramik (jenis dan warna glasiar), asal-usul dan pentarikhan seramik perdagangan China yang dijumpa di Sungai Sadong. This thesis discusses the results of the study on the Chinese trade ceramics found in Senangeh, Benat Hilir and Gedong on the Sungai Sadong, Sarawak. The methodology used in this study included morphology analysis, scientific analysis and comparative studies, in order to answer questions concerning the classification (such as types and glaze colours), origins and date of production of the ceramics

Logarithmic singularities and quantum oscillations in magnetically doped topological insulators

We report magnetotransport measurements on magnetically doped (Bi,Sb)$_2$Te$_3$ films grown by molecular beam epitaxy. In Hallbar devices, logarithmic dependence on temperature and bias voltage are obseved in both the longitudinal and anomalous Hall resistance. The interplay of disorder and electron-electron interactions is found to explain quantitatively the observed logarithmic singularities and is a dominant scattering mechanism in these samples. Submicron scale devices exhibit intriguing quantum oscillations at high magnetic fields with dependence on bias voltage. The observed quantum oscillations can be attributed to bulk and surface transport.Comment: 10 pages, 13 figure

Prospects for detection of Υ(1D)→Υ(1S)ππ\Upsilon(1D) \to \Upsilon(1S) \pi \pi via Υ(3S)→Υ(1D)+X\Upsilon(3S) \to \Upsilon(1D) + X

At least one state in the first family of D-wave $b \bar b$ quarkonium levels has been discovered near the predicted mass of 10.16 GeV/$c^2$. This state is probably the one with J=2. This state and the ones with J=1 and J=3 may contribute a detectable amount to the decay $\Upsilon(1D) \to \Upsilon(1S) \pi \pi$, depending on the partial widths for these decays for which predictions vary considerably. The prospects for detection of the chain $\Upsilon(3S) \to \Upsilon(1D) + X \to \Upsilon \pi \pi + X$ are discussed.Comment: 4 pages, LaTeX, 1 figure, to be published in Phys. Rev. D, comment added after Eq. (2

Minor Review: An Overview of a Synthetic Nanophase Bone Substitute

Material is reviewed that consists of reconstituted collagen fibril gel mineralized in a manner that produces biomimetically sized nanoapatites intimately associated with the fibrils. This gel is formed into usable shapes with a modulus and strength that allow it to be surgically press fitted into bony defects. The design paradigm for the material is that the nanoapatites will dissolve into soluble Ca2+ as the collagen is degraded into RGD-containing peptide fragments due to osteoclastic action. This is intended to signal to the osteoclasts to continue removing the material in a biomimetic fashion similar to bony remodeling. Preliminary experiments in a subcutaneous rat model show that the material is biocompatible with respect to inflammatory and immunogenic responses, and that it supports cellular invasion. Preliminary experiments in a critical-sized mandibular defect in rats show that the material is resorbable and functions well as a bone morphogenetic 2 (BMP-2) carrier. We have produced a range of mechanical and biological responses by varying mechanical and chemical processing of the material

Colour contrast sensitivity in eyes at high risk of neovascular age-related macular degeneration

Purpose: To generate the first published reference database of colour contrast sensitivity in eyes at high risk of neovascular age-related macular degeneration and to explore this important feature in quality of vision. Background: Quality of vision depends on many factors. Changes in chromatic contrast sensitivity remain largely unexplored in eyes at high risk of neovascular age-related macular degeneration; they may however not only be relevant for quality of life but also an early indicator of the onset of the disease, so it is important to have a means to evaluate any variation in colour contrast sensitivity, especially in view of the likely increase in neovascular age-related macular degeneration as the population ages. Methods: This prospective longitudinal study evaluated colour contrast sensitivity along the protan and tritan colour axes in 145 eyes at high risk of neovascular age-related macular degeneration. Results: Colour contrast sensitivity showed statistically significant correlations with age and visual acuity, but not gender nor laterality (i.e. whether the right or left eye was being tested). There was significant variability among individuals, especially for the tritan axis, with some subjects well within normal limits for age and others with very poor colour contrast sensitivity. Conclusion: This study has generated the first published colour contrast sensitivity reference database for eyes at high risk of neovascular age-related macular degeneration. It has also shown a high inter-individual variability of colour contrast sensitivity in eyes at high risk of neovascular age-related macular degeneration, but the significance of this is unclear. Further work is required to establish if eyes with high colour contrast sensitivity thresholds (i.e. poor colour vision) have a higher risk of developing neovascular age-related macular degeneration over time, and this is the subject of ongoing work