Focal shift in focused radially polarized ultrashort pulsed laser beams

Beginning with a beam coherence polarization (BCP) matrix, we obtain an analytical intensity expression for radially polarized ultrashort pulsed laser beams that pass through an apertureless aplanatic lens. We also investigate the intensity distribution of radially polarized beams in the vicinity of the focus. The focal shift of these beams is studied in detail. The focal shift depends strongly on Z(F) that coincides with pi times the Fresnel number. (c) 2007 Optical Society of America.

Design and development of compact optical systems = Diseño y desarrollo de sistemas ópticos compactos

Esta tesis considera dos tipos de aplicaciones del diseño óptico: óptica formadora de imagen por un lado, y óptica anidólica (nonimaging) o no formadora de imagen, por otro. Las ópticas formadoras de imagen tienen como objetivo la obtención de imágenes de puntos del objeto en el plano de la imagen. Por su parte, la óptica anidólica, surgida del desarrollo de aplicaciones de concentración e iluminación, se centra en la transferencia de energía en forma de luz de forma eficiente. En general, son preferibles los diseños ópticos que den como resultado sistemas compactos, para ambos tipos de ópticas (formadora de imagen y anidólica). En el caso de los sistemas anidólicos, una óptica compacta permite tener costes de producción reducidos. Hay dos razones: (1) una óptica compacta presenta volúmenes reducidos, lo que significa que se necesita menos material para la producción en masa; (2) una óptica compacta es pequeña y ligera, lo que ahorra costes en el transporte. Para los sistemas ópticos de formación de imagen, además de las ventajas anteriores, una óptica compacta aumenta la portabilidad de los dispositivos, que es una gran ventaja en tecnologías de visualización portátiles, tales como cascos de realidad virtual (HMD del inglés Head Mounted Display). Esta tesis se centra por tanto en nuevos enfoques de diseño de sistemas ópticos compactos para aplicaciones tanto de formación de imagen, como anidólicas. Los colimadores son uno de los diseños clásicos dentro la óptica anidólica, y se pueden utilizar en aplicaciones fotovoltaicas y de iluminación. Hay varios enfoques a la hora de diseñar estos colimadores. Los diseños convencionales tienen una relación de aspecto mayor que 0.5. Con el fin de reducir la altura del colimador manteniendo el área de iluminación, esta tesis presenta un diseño de un colimador multicanal. En óptica formadora de imagen, las superficies asféricas y las superficies sin simetría de revolución (o freeform) son de gran utilidad de cara al control de las aberraciones de la imagen y para reducir el número y tamaño de los elementos ópticos. Debido al rápido desarrollo de sistemas de computación digital, los trazados de rayos se pueden realizar de forma rápida y sencilla para evaluar el rendimiento del sistema óptico analizado. Esto ha llevado a los diseños ópticos modernos a ser generados mediante el uso de diferentes técnicas de optimización multi-paramétricas. Estas técnicas requieren un buen diseño inicial como punto de partida para el diseño final, que será obtenido tras un proceso de optimización. Este proceso precisa un método de diseño directo para superficies asféricas y freeform que den como resultado un diseño cercano al óptimo. Un método de diseño basado en ecuaciones diferenciales se presenta en esta tesis para obtener un diseño óptico formado por una superficie freeform y dos superficies asféricas. Esta tesis consta de cinco capítulos. En Capítulo 1, se presentan los conceptos básicos de la óptica formadora de imagen y de la óptica anidólica, y se introducen las técnicas clásicas del diseño de las mismas. El Capítulo 2 describe el diseño de un colimador ultra-compacto. La relación de aspecto ultra-baja de este colimador se logra mediante el uso de una estructura multicanal. Se presentará su procedimiento de diseño, así como un prototipo fabricado y la caracterización del mismo. El Capítulo 3 describe los conceptos principales de la optimización de los sistemas ópticos: función de mérito y método de mínimos cuadrados amortiguados. La importancia de un buen punto de partida se demuestra mediante la presentación de un mismo ejemplo visto a través de diferentes enfoques de diseño. El método de las ecuaciones diferenciales se presenta como una herramienta ideal para obtener un buen punto de partida para la solución final. Además, diferentes técnicas de interpolación y representación de superficies asféricas y freeform se presentan para el procedimiento de optimización. El Capítulo 4 describe la aplicación del método de las ecuaciones diferenciales para un diseño de un sistema óptico de una sola superficie freeform. Algunos conceptos básicos de geometría diferencial son presentados para una mejor comprensión de la derivación de las ecuaciones diferenciales parciales. También se presenta un procedimiento de solución numérica. La condición inicial está elegida como un grado de libertad adicional para controlar la superficie donde se forma la imagen. Basado en este enfoque, un diseño anastigmático se puede obtener fácilmente y se utiliza como punto de partida para un ejemplo de diseño de un HMD con una única superficie reflectante. Después de la optimización, dicho diseño muestra mejor rendimiento. El Capítulo 5 describe el método de las ecuaciones diferenciales ampliado para diseños de dos superficies asféricas. Para diseños ópticos de una superficie, ni la superficie de imagen ni la correspondencia entre puntos del objeto y la imagen pueden ser prescritas. Con esta superficie adicional, la superficie de la imagen se puede prescribir. Esto conduce a un conjunto de tres ecuaciones diferenciales ordinarias implícitas. La solución numérica se puede obtener a través de cualquier software de cálculo numérico. Dicho procedimiento también se explica en este capítulo. Este método de diseño da como resultado una lente anastigmática, que se comparará con una lente aplanática. El diseño anastigmático converge mucho más rápido en la optimización y la solución final muestra un mejor rendimiento. ABSTRACT We will consider optical design from two points of view: imaging optics and nonimaging optics. Imaging optics focuses on the imaging of the points of the object. Nonimaging optics arose from the development of concentrators and illuminators, focuses on the transfer of light energy, and has wide applications in illumination and concentration photovoltaics. In general, compact optical systems are necessary for both imaging and nonimaging designs. For nonimaging optical systems, compact optics use to be important for reducing cost. The reasons are twofold: (1) compact optics is small in volume, which means less material is needed for mass-production; (2) compact optics is small in size and light in weight, which saves cost in transportation. For imaging optical systems, in addition to the above advantages, compact optics increases portability of devices as well, which contributes a lot to wearable display technologies such as Head Mounted Displays (HMD). This thesis presents novel design approaches of compact optical systems for both imaging and nonimaging applications. Collimator is a typical application of nonimaging optics in illumination, and can be used in concentration photovoltaics as well due to the reciprocity of light. There are several approaches for collimator designs. In general, all of these approaches have an aperture diameter to collimator height not greater than 2. In order to reduce the height of the collimator while maintaining the illumination area, a multichannel design is presented in this thesis. In imaging optics, aspheric and freeform surfaces are useful in controlling image aberrations and reducing the number and size of optical elements. Due to the rapid development of digital computing systems, ray tracing can be easily performed to evaluate the performance of optical system. This has led to the modern optical designs created by using different multi-parametric optimization techniques. These techniques require a good initial design to be a starting point so that the final design after optimization procedure can reach the optimum solution. This requires a direct design method for aspheric and freeform surface close to the optimum. A differential equation based design method is presented in this thesis to obtain single freeform and double aspheric surfaces. The thesis comprises of five chapters. In Chapter 1, basic concepts of imaging and nonimaging optics are presented and typical design techniques are introduced. Readers can obtain an understanding for the following chapters. Chapter 2 describes the design of ultra-compact collimator. The ultra-low aspect ratio of this collimator is achieved by using a multichannel structure. Its design procedure is presented together with a prototype and its evaluation. The ultra-compactness of the device has been approved. Chapter 3 describes the main concepts of optimizing optical systems: merit function and Damped Least-Squares method. The importance of a good starting point is demonstrated by presenting an example through different design approaches. The differential equation method is introduced as an ideal tool to obtain a good starting point for the final solution. Additionally, different interpolation and representation techniques for aspheric and freeform surface are presented for optimization procedure. Chapter 4 describes the application of differential equation method in the design of single freeform surface optical system. Basic concepts of differential geometry are presented for understanding the derivation of partial differential equations. A numerical solution procedure is also presented. The initial condition is chosen as an additional freedom to control the image surface. Based on this approach, anastigmatic designs can be readily obtained and is used as starting point for a single reflective surface HMD design example. After optimization, the evaluation shows better MTF. Chapter 5 describes the differential equation method extended to double aspheric surface designs. For single optical surface designs, neither image surface nor the mapping from object to image can be prescribed. With one more surface added, the image surface can be prescribed. This leads to a set of three implicit ordinary differential equations. Numerical solution can be obtained by MATLAB and its procedure is also explained. An anastigmatic lens is derived from this design method and compared with an aplanatic lens. The anastigmatic design converges much faster in optimization and the final solution shows better performance.

Aplanatic thin TIR lens

Aplanatic designs present great interest in the optics field since they are free from spherical aberration and linear coma at the axial direction. Nevertheless nowadays it cannot be found on literature any thin aplanatic design based on a lens. This work presents the first aplanatic thin lens (in this case a dome-shaped faceted TIR lens performing light collimation), designed for LED illumination applications. This device, due to its TIR structure (defined as an anomalous microstructure as we will see) presents good color-mixing properties. We will show this by means of raytrace simulations, as well as high optical efficiency.

Determination of electric field at and near the focus of a cylindrical lens for applications in fluorescence microscopy

We present an explicit computable integral solution of the electric field generated at the focal region of a cylindrical lens. This representation is based on vectorial diffraction theory and further enables the computation of the system point spread function of a cylindrical lens. It is assumed that there is no back-scattering and the contribution from the evanescent field is negligible. Stationary phase approximation along with the Fresnel transmission coefficients are employed for evaluating the polarization dependent electric field components. Studies were carried out to determine the polarization effects and to calculate the system resolution. The effect of s -, p - and randomly polarized light is studied on the fixed sample (electric dipole is fixed in space). Proposed approach allows better understanding of electric field effects at the focus of a cylindrical aplanatic system. This opens up future developments in the field of fluorescence microscopy and optical imaging. (C) 2013 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Applying an equity lens to tobacco-control policies and their uptake in six western-european countries

We identified policies that may be effective in reducing smoking among socioeconomically disadvantaged groups, and examined trends in their level of application between 1985 and 2000 in six western-European countries (Sweden, Finland, the United Kingdom, the Netherlands, Germany, and Spain). We located studies from literature searches in major databases, and acquired policy data from international data banks and questionnaires distributed to tobacco policy organisations/researchers. Advertising bans, smoking bans in workplaces, removing barriers to smoking cessation therapies, and increasing the cost of cigarettes have the potential to reduce socioeconomic inequalities in smoking. Between 1985 and 2000, tobacco control policies in most countries have become more targeted to decrease the smoking behaviour of low-socioeconomic groups. Despite this, many national tobacco-control strategies in western-European countries still fall short of a comprehensive policy approach to addressing smoking inequalities.

The lens of ludic engagement : evaluating participation in interactive art installations

Designers and artists have integrated recent advances in interactive, tangible and ubiquitous computing technologies to create new forms of interactive environments in the domains of work, recreation, culture and leisure. Many designs of technology systems begin with the workplace in mind, and with function, ease of use, and efficiency high on the list of priorities. [1] These priorities do not fit well with works designed for an interactive art environment, where the aims are many, and where the focus on utility and functionality is to support a playful, ambiguous or even experimental experience for the participants. To evaluate such works requires an integration of art-criticism techniques with more recent Human Computer Interaction (HCI) methods, and an understanding of the different nature of engagement in these environments. This paper begins a process of mapping a set of priorities for amplifying engagement in interactive art installations. I first define the concept of ludic engagement and its usefulness as a lens for both design and evaluation in these settings. I then detail two fieldwork evaluations I conducted within two exhibitions of interactive artworks, and discuss their outcomes and the future directions of this research.

At breaking point? Challenges for Australian film policy through the lens of genre (horror) films

Cultural policy settings attempting to foster the growth and development of the Australian feature film industry in era of globalisation are coming under increasing pressure. Global forces and emerging production and distribution models are challenging the “narrowness” of cultural policy – mandating a particular film culture, circumscribing certain notions of value and limiting the variety of films produced through cultural policy driven subvention models. Australian horror film production is an important case study. Horror films are a production strategy well suited to the financial limitations of the Australian film industry with competitive advantages for producers against international competitors. However, emerging within a “national” cinema driven by public subsidy and social/cultural objectives, horror films – internationally oriented with a low-culture status – have been severely marginalised within public funding environments. This paper introduces Australian horror film production, and examines the limitations of cultural policy, and the impacts of these questions for the Producer Offset.

Encounters and content sharing in an urban village : reading texts through an archaeological lens

Archaeology provides a framework of analysis and interpretation that is useful for disentangling the textual layers of a contemporary lived-in urban space. The producers and readers of texts may include those who planned and developed the site and those who now live, visit and work there. Some of the social encounters and content sharing between these people may be artificially produced or manufactured in the hope that certain social situations will occur. Others may be serendipitous. With archaeology’s original focus on places that are no longer inhabited it is often only the remaining artefacts and features of the built environment that form the basis for interpreting the social relationships of past people. Our analysis however, is framed within a contemporary notion of archaeological artefacts in an urban setting. Unlike an excavation, where the past is revealed through digging into the landscape, the application of landscape archaeology within a present day urban context is necessarily more experiential, visual and based on recording and analysing the physical traces of social encounters and relationships between residents and visitors. These physical traces are present within the creative content, and the built and natural elements of the environment. This chapter explores notions of social encounters and content sharing in an urban village by analysing three different types of texts: the design of the built environment; content produced by residents through a geospatial web application; and, print and online media produced in digital storytelling workshops.

Age-related development of a refractive index plateau in the human lens : evidence for a distinct nucleus

The human lens comprises two distinct regions in which the refractive index changes at different rates. The periphery contains a rapidly increasing refractive index gradient, which becomes steeper with age. The inner region contains a shallow gradient, which flattens with age, due to formation of a central plateau, of RI = 1.418, which reaches a maximum size of 7.0 × 3.05 mm around age 60 years. Formation of the plateau can be attributed to compression of fibre cells generated in prenatal life. Present in prenatal but not in postnatal fibre cells, γ-crystallin may play a role in limiting nuclear cell compression.

Mathematical models for describing the shape of the in vitro unstretched human crystalline lens

We developed orthogonal least-squares techniques for fitting crystalline lens shapes, and used the bootstrap method to determine uncertainties associated with the estimated vertex radii of curvature and asphericities of five different models. Three existing models were investigated including one that uses two separate conics for the anterior and posterior surfaces, and two whole lens models based on a modulated hyperbolic cosine function and on a generalized conic function. Two new models were proposed including one that uses two interdependent conics and a polynomial based whole lens model. The models were used to describe the in vitro shape for a data set of twenty human lenses with ages 7–82 years. The two-conic-surface model (7 mm zone diameter) and the interdependent surfaces model had significantly lower merit functions than the other three models for the data set, indicating that most likely they can describe human lens shape over a wide age range better than the other models (although with the two-conic-surfaces model being unable to describe the lens equatorial region). Considerable differences were found between some models regarding estimates of radii of curvature and surface asphericities. The hyperbolic cosine model and the new polynomial based whole lens model had the best precision in determining the radii of curvature and surface asphericities across the five considered models. Most models found significant increase in anterior, but not posterior, radius of curvature with age. Most models found a wide scatter of asphericities, but with the asphericities usually being positive and not significantly related to age. As the interdependent surfaces model had lower merit function than three whole lens models, there is further scope to develop an accurate model of the complete shape of human lenses of all ages. The results highlight the continued difficulty in selecting an appropriate model for the crystalline lens shape.

Repeatability and validity of lens densitometry measured with Scheimpflug imaging

Purpose To assess the repeatability and validity of lens densitometry derived from the Pentacam Scheimpflug imaging system. Setting Eye Clinic, Queensland University of Technology, Brisbane, Australia. Methods This prospective cross-sectional study evaluated 1 eye of subjects with or without cataract. Scheimpflug measurements and slitlamp and retroillumination photographs were taken through a dilated pupil. Lenses were graded with the Lens Opacities Classification System III. Intraobserver and interobserver reliability of 3 observers performing 3 repeated Scheimpflug lens densitometry measurements each was assessed. Three lens densitometry metrics were evaluated: linear, for which a line was drawn through the visual axis and a mean lens densitometry value given; peak, which is the point at which lens densitometry is greatest on the densitogram; 3-dimensional (3D), in which a fixed, circular 3.0 mm area of the lens is selected and a mean lens densitometry value given. Bland and Altman analysis of repeatability for multiple measures was applied; results were reported as the repeatability coefficient and relative repeatability (RR). Results Twenty eyes were evaluated. Repeatability was high. Overall, interobserver repeatability was marginally lower than intraobserver repeatability. The peak was the least reliable metric (RR 37.31%) and 3D, the most reliable (RR 5.88%). Intraobserver and interobserver lens densitometry values in the cataract group were slightly less repeatable than in the noncataract group. Conclusion The intraobserver and interobserver repeatability of Scheimpflug lens densitometry was high in eyes with cataract and eyes without cataract, which supports the use of automated lens density scoring using the Scheimpflug system evaluated in the study

Bifocal lens control of myopia progression in children

This research investigated underlying issues that were critical to the success of the bifocal trial and comprised of three studies. The first study evaluated if Chinese-Canadian children were suitable subjects for the bifocal trial. The high prevalence of myopia in Chinese children suggests that genetic input plays a role in myopia development, but the rapid increase in prevalence over the last few decades indicates environmental factors are also important. Since this bifocal trial was conducted in Canada, this work aimed to determine whether Chinese children who had migrated to Canada would still have high myopia prevalence and a high rate of myopia progression. The second study determined the optimal bifocal lens power for myopia treatment and the effect of incorporating base-in prism into the bifocal. In the majority of published myopia control studies, the power of the prescribed near addition was usually predetermined in the belief that the near addition would always help to improve the near focus. In fact, the effect of near addition on the accommodative error might be quite different even for individuals in which the same magnitude of accommodation lag had been measured. Therefore, this work was necessary to guide the selection of bifocal and prism powers most suitable for the subsequent bifocal trial. The third study, the ultimate goal of this research, was to conduct a longitudinal clinical trial to determine if bifocals and prismatic bifocals could control myopia progression in children.

A qualitative investigation of sources of value in social marketing from the lens of a public health service

This paper seeks to identify the sources of value in a government health screening service. Consumers' use of such services for their won benefits demonstrates desirable behaviour and their continued use of these services indicates maintenance of the behaviour. There are also positive outcomes for society as the health of its members is improved overall through this behaviour. Individual-depth interview with 25 women who use breast cancer screening services provided by BreastScreen (BSQ) revealed five categories of sources of value. They are information sources, interaction sources, service, environment, and consumer participation. These findings provide valuable insights into the value construction of consumers and contribute towards our understanding of the value concept in social marketing.