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Author

Michael R. Gleeson

Other affiliations:Β National University of Ireland
Bio: Michael R. Gleeson is an academic researcher from Maynooth University. The author has contributed to research in topics: Excited state & Holographic grating. The author has an hindex of 4, co-authored 17 publications receiving 179 citations. Previous affiliations of Michael R. Gleeson include National University of Ireland.

Papers
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Journal Articleβ€’DOIβ€’
TL;DR: A brief review of the optimisation of photopolymer materials for holographic data storage (HDS) applications is described and the key contributions of each work examined and many of the suggestions made for the improvement of the different photopolymers discussed are presented.
Abstract: Photopolymers are very interesting as optically sensitive recording media due to the fact that they are inexpensive, self-processing materials with the ability to capture low-loss, high-fidelity volume recordings of 3D illuminating patterns. We have prepared this paper in part in order to enable the recognition of outstanding issues, which limit in particular the data storage capacity in holographic data storage media. In an attempt to further develop the data storage capacity and quality of the information stored, that is, the material sensitivity and resolution, a deeper understanding of such materials in order to improve them has become ever more crucial. In this paper a brief review of the optimisation of photopolymer materials for holographic data storage (HDS) applications is described. The key contributions of each work examined and many of the suggestions made for the improvement of the different photopolymer material discussed are presented.

93Β citations

Journal Articleβ€’DOIβ€’
TL;DR: In this paper, two rates, π‘˜π‘Žπ‘† and ǫ𝑾, were proposed to estimate the rate constants of photon absorption in going from ground state to the singlet and triplet states, respectively.
Abstract: Several studies of the time varying photon absorption effects, which occur during the photoinitiation process involving in photopolymer materials, have been presented. Three primary mechanisms have been identified: (i) the dye absorption, (ii) recovery, and (iii) bleaching. Based on an analysis of these mechanisms, the production of primary radicals can be physically described and modelled. In free radical photopolymerization systems, the excited dye molecules induce the production of the primary radicals, 𝑅‒, which are key in determining how many monomers are polymerized. This, in turn, is closely related to the refractive index modulation formed during holographic recording. In this paper, to avoid the complexities involved in estimating the rate constant of intersystem crossing, π‘˜π‘ π‘‘, in going from the excited singlet state dye to the excited triplet state dye, we introduce two rates, π‘˜π‘Žπ‘† and π‘˜π‘Žπ‘‡ these are the proposed rate constants of photon absorption in going from the ground state to the singlet and triplet states, respectively. Using the resulting model, four kinds of Xanthene dyes: Erythrosin B; Eosin Y; Phloxine B, Rose Bengal, and one Thiazine dye: Methylene Blue, are experimentally characterised for use in an AA/PVA photopolymer.

41Β citations

Journal Articleβ€’DOIβ€’
TL;DR: This Non-local Photo-polymerisation Driven Diffusion model is explored, illustrating some of the useful trends, which the model predicts and their implications on the improvement of photopolymer material performance are analyzed.
Abstract: An understanding of the photochemical and photo-physical processes, which occur during photopolymerization is of extreme importance when attempting to improve a photopolymer material's performance for a given application. Recent work carried out on the modelling of the mechanisms which occur in photopolymers during- and post-exposure, has led to the development of a tool, which can be used to predict the behaviour of these materials under a wide range of conditions. In this paper, we explore this Non-local Photo-polymerisation Driven Diffusion model, illustrating some of the useful trends, which the model predicts and we analyse their implications on the improvement of photopolymer material performance.

37Β citations

Proceedings Articleβ€’DOIβ€’
08 Jun 2005
TL;DR: In this article, a nonlocal spatial response function was proposed to predict high spatial frequency cut-off in photopolymers and more recently it has been shown that use of the nonlocal model is necessary to accurately predict higher order grating components.
Abstract: The inclusion of a nonlocal spatial response function in the Nonlocal Polymer Driven Diffusion model (NPDD) has been shown to predict high spatial frequency cut-off in photopolymers and more recently it has been shown that use of the nonlocal model is necessary to accurately predict higher order grating components. Here the nature of the temporal response of photopolymer is discussed and a nonlocal temporal response function proposed. The extended model is then solved using a finite element technique and the results discussed. Based on this model we examine the nature of grating evolution when illumination is stopped during the grating recording process. Refractive indices of the components of the photopolymer material used are determined and predictions of the temporal evolution of the refractive index modulation described. Material parameters are then extracted based on fits to experimental data for non-linear and both ideal and non-ideal kinetic models.

5Β citations

Proceedings Articleβ€’DOIβ€’
TL;DR: In this paper, a non-local photo-polymerization-driven diffusion (NPDD) model is proposed to reduce the non-locality of polymer chain growth and improve the spatial frequency response of a photopolymer material.
Abstract: The Non-local Photo-Polymerization Driven Diffusion (NPDD) model indicates how a material’s performance might be improved, and provides a tool for quantitive comparison of different material compositions and to predict their fundamental limits. In order to reduce the non-locality of polymer chain growth (i.e the non-local response parameter, Οƒ) and to improve the spatial frequency response of a photopolymer material, we introduce the chain transfer agent (CTA). In the literature, extensive studies have been carried out on the improvements of the non-local response modifying by the CTA, sodium formate, in the polyvinyl alcohol-acrylamide (PVA/AA) material. In this article, i) based on the chemical reactions of CTA, we extended the CTA model in the literature; ii) we compare two different CTA materials, sodium formate and 1-mercapto-2-propanol without cross-linker in order to obtain the experimental confirmation of the reduction in the average polymer molecular weight is provided using a diffusion-based holographic technique; iii) we examine the non-local responses of several spatial frequencies with the two CTAs. Using the extended CTA model it is demonstrated that the CTA has the effect of decreasing the average length of the polyacrylamide (PA) chains formed, thus reducing the non-local response parameter, especially, in the high spatial frequency case.

4Β citations


Cited by
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Journal Articleβ€’DOIβ€’

[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i β€”the square root of minus one, which seems an odd beast at that timeβ€”an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i β€”the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that timeβ€”an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785Β citations

Journal Articleβ€’DOIβ€’
Jianghao Xiong1, En-Lin Hsiang1, Ziqian He1, Tao Zhan1, Shin-Tson Wu1Β β€’
TL;DR: In this article, the basic structures of AR and VR headsets and operation principles of various holographic optical elements (HOEs) and lithography-enabled devices are described, with detailed description and analysis of some state-of-the-art architectures.
Abstract: With rapid advances in high-speed communication and computation, augmented reality (AR) and virtual reality (VR) are emerging as next-generation display platforms for deeper human-digital interactions. Nonetheless, to simultaneously match the exceptional performance of human vision and keep the near-eye display module compact and lightweight imposes unprecedented challenges on optical engineering. Fortunately, recent progress in holographic optical elements (HOEs) and lithography-enabled devices provide innovative ways to tackle these obstacles in AR and VR that are otherwise difficult with traditional optics. In this review, we begin with introducing the basic structures of AR and VR headsets, and then describing the operation principles of various HOEs and lithography-enabled devices. Their properties are analyzed in detail, including strong selectivity on wavelength and incident angle, and multiplexing ability of volume HOEs, polarization dependency and active switching of liquid crystal HOEs, device fabrication, and properties of micro-LEDs (light-emitting diodes), and large design freedoms of metasurfaces. Afterwards, we discuss how these devices help enhance the AR and VR performance, with detailed description and analysis of some state-of-the-art architectures. Finally, we cast a perspective on potential developments and research directions of these photonic devices for future AR and VR displays.

219Β citations

Patentβ€’
10 May 2013
TL;DR: In this paper, an eye tracker having a waveguide for propagating illumination light towards an eye and propagating image light reflected from at least one surface of an eye is defined.
Abstract: An eye tracker having a waveguide for propagating illumination light towards an eye and propagating image light reflected from at least one surface of an eye, a light source optically coupled to the waveguide, and a detector optically coupled to the waveguide. Disposed in the waveguide is at least one grating lamina for deflecting the illumination light towards the eye along a first waveguide path and deflecting the image light towards the detector along a second waveguide path.

146Β citations

Patentβ€’
22 Aug 2012
TL;DR: In this article, the authors provided a transparent wearable data display consisting of a source of collimated light, a means for deflecting said light into a scanned beam, a first array comprising one column and integer N TOWS of switchable grating elements sandwiched between first and second parallel transparent substrates, the substrates together functioning as a first light guide, an second array comprising M columns and N rows of switchables sandwiched by third and fourth, parallel transparent substrate, the substrate acting as a second light guide; and transparent electrodes applied to opposing faces of the first and
Abstract: There is provided a transparent wearable data display comprising: a source of collimated light; a means for deflecting said collimated light into a scanned beam; a first array comprising one column and integer N TOWS of switchable grating elements sandwiched between first and second parallel transparent substrates, the substrates together functioning as a first light guide; an second array comprising M columns and N rows of switchable grating elements sandwiched between third and fourth, parallel transparent substrates the substrates together functioning as a second light guide; transparent electrodes applied to opposing faces of the first and second and the third and fourth substrates. Hie apparatus further comprises a first coupling means tor directing the scanned beam into a first TIR light path between the outer surfaces of the first lightguide along the first array column; and a second coupling means for directing the first HR light into a second TIR path between the outer surfaces of the second lightguide along a row of elements of the second array.

130Β citations

Patentβ€’
19 May 2014
TL;DR: In this paper, an eye tracker has a first waveguide for propagating illumination light along a first-waveguide path and propagating image light reflected from at least one surface of an eye along a second waveguide path.
Abstract: An eye tracker having a first waveguide for propagating illumination light along a first waveguide path and propagating image light reflected from at least one surface of an eye along a second waveguide path. At least one grating lamina for deflecting the illumination light out of the first waveguide path towards the eye and deflecting the image light into the second waveguide path towards a detector is disposed adjacent an optical surface of the waveguide.

108Β citations