Search

In the present work, the viability of a novel recording geometry to produce reflection holographic couplers is analyzed. Recalling the idea of previous works, photopolymers are used as the recording material because they have been proven to be well-suited for the intended see-through application: the capability to provide a virtual image without compromising the information about the surrounding environment. Moreover, holography fundamentals give us the proper background to examine the proposed design, where no prisms or microlenses arrays are used. Aiming to support the analysis, we provide experimental evidence that the produced reflection holographic gratings exhibit the correct properties to work as a coupler, where the sensitivity of the material and its properties are studied and examined.

The study of liquid crystal (LC) director distribution is an important area of research in materials science and technology. Parallel-aligned liquid crystal (PA-LC) devices have been extensively studied due to their applications in liquid crystal displays, optical devices, and sensors. Estimating the LC director distribution is a critical step in designing and optimising PA-LC devices. This work shows the results derived from apply-ing novel optimisation techniques to estimate the liquid crystal (LC) director distribution in parallel-aligned liquid crystal (PA-LC) devices. Moreover, the genetic algorithm (GA) has been applied and compared with the minimisation of the Frank-Oseen free energy through the Euler-Lagrange equations. The GA is a stochastic optimisation technique that can effectively explore the search space and find the global optimum. Overall, this study’s results demonstrate the GA’s effectiveness in estimating the LC director distribution in PA-LC devices. This approach can improve the performance and design of liquid crystal displays, optical devices, and sensors. Furthermore, it can be extended to other fields where the optimisation of complex systems is required. Further research is needed to optimise the GA parameters and to explore its potential in other applications.

In the present work, the viability of a novel recording geometry to produce reflection holographic couplers is analyzed. Recalling the idea of previous works, photopolymers are used as the recording material, as they are well-suited for the intended see-through application. Moreover, Kogelnik’s theory fundamentals give us the proper background to examine the proposed design, where no prisms or microlenses arrays are used. Aiming to support the analysis, we provide experimental evidence that the produced gratings exhibit the correct properties to work as a coupler.

A technique to evaluate the refractive index, the absorption coefficient and the thickness of holographic recording materials is presented. The materials are in the form of a thin layer of film deposited on a thick glass plate. The experimental reflectances of p-polarized light are measured as a function of the incident angle, and the values of refractive index, thickness and absorption coefficient of the layer are obtained using the theoretical equation for reflectance. As examples, holographic silver halide emulsions and photopolymers are analyzed. The agreement between the calculated reflectances, using the thickness and refractive index obtained, and the measured reflectances is satisfactory.Se presenta una técnica experimental para determinar el índice de refracción, el coeficiente de absorción y el espesor de materiales de registro holográfico. Los materiales están depositados como capas finas sobre una lámina planoparalela de vidrio. Se determina experimentalmente la reflectancia en función del ángulo de incidencia para luz polarizada linealmente paralela al plano de incidencia, de modo que los valores del índice de refracción, el coeficiente de absorción y el espesor se obtienen ajustando la ecuación de la reflectancia teórica a los datos experimentales. Como ejemplos se han analizado emulsiones fotográficas y fotopolímeros, obteniéndose un buen ajuste entre la función teórica y los datos experimentales.

One of the most interesting techniques for the production of holographic optical elements is silver halide sensitised gelatin (SHSG). It combines the high sensitivity of photographic emulsions with the well-known low scattering and high diffraction efficiencies corresponding to dichromated gelatin. In this work we made a comparative study on SHSG holograms recorded on three different red sensitive emulsions: Agfa 8E75 HD, Slavich PFG-01 and BB-640 . The influence of the degree of hardening of the gelatin and the size and concentration of silver halide grains in the SHSG proccess is studied. And we will show that real high diffraction efficiencies can be obtained when using BB-640 and Slavich PFG-01 plates for recording phase transmission holograms (as high as 93% for PFG-01 and 90% for BB-640, allowing for reflections). Our investigations reveal that PFG-01 and BB-640 emulsions are not only a substitution to Agfa material, but may offer better results at a moment in which Agfa has stopped its production of holographic material.Una de las técnicas más interesantes para la obtención de elementos ópticos holográficos es la gelatina sensibilizada de haluro de plata (GSHP). Esta técnica combina la alta sensibilidad de las emulsiones fotográficas con los conocidos altos rendimientos en difracción y bajos niveles de scattering correspondientes a la gelatina dicromatada. En este trabajo se ha hecho un estudio comparativo sobre hologramas en gelatina sensibilizada de haluro de plata registrados en tres emulsiones diferentes sensibles al rojo: Agfa 8E75 HD, Slavich PFG-01 y BB-640. En dicho estudio se ha analizado la influencia del grado de endurecido de la gelatina y la concentración y el tamaño de los granos de haluro de plata en el procesado GHSP. Se obtuvieron rendimientos en difracción realmente altos cuando se utilizaron las placas BB-640 y Slavich PFG-01 para el registro de hologramas de fase por transmisión (tan altos como el 93% para las PFG-01 y el 90% para las BB-640, después de haber corregido los resultados teniendo en cuenta las reflexiones en las distintas superficies de separación de la placa). Nuestras investigaciones indican que las emulsiones BB-640 y Slavich PFG-01 pueden cubrir el vacío dejado por las placas Agfa 8E75 HD, e incluso pueden ofrecer mejores resultados en un momento en el cual Agfa ha dejado de fabricar material para aplicaciones en Holografía.

This work introduces a novel computational approach based on Principal Component Analysis (PCA) for dimensionality reduction of the solution space in optimisation problems with known linear interdependencies among solution variables. By creating synthetic datasets with deliberately engineered properties and applying PCA, the solution space's remapping significantly reduces its dimensionality, leading to faster computation and more robust convergence in optimisation processes. We demonstrate this method by integrating it with a Genetic Algorithm (GA) for solving the optimal director distribution in liquid crystal (LC) devices, specifically addressing 2D and complex 3D spatial light modulator (SLM) structures such as twisted nematic liquid crystals (TN-LC) and parallel-aligned liquid crystal on silicon (PA-LCoS), respectively. The phase profiles obtained from the director vector distributions for horizontal and vertical high-frequency binary phase gratings closely match the theoretical values derived from minimising the traditional elastic Frank–Oseen functional via Euler–Lagrange equations. Beyond this specific application, our method offers a general framework for reducing computational complexity in optimisation problems by directly reducing the dimensionality of the solution space. This approach is applicable across various optimisation scenarios with well-known linear interdependencies among solution variables, enabling significant reductions in computational costs and improvements in robustness and convergence. [ABSTRACT FROM AUTHOR]

In this work we present a formalism based on scalar Green's functions to deal with electromagnetic scattering problems. Although the formulations of the Mie theory and Born approximations in terms of electromagnetic scattering are well known and relevant, they have certain disadvantages: complexity, computational time, few symmetries, etc. Therefore, the study with scalar Green's functions allows dealing with these problems with greater simplicity and efficiency. However, the information provided by the vector formulation is sacrificed. Nevertheless, different cases of electromagnetic scattering of dielectric media with different dimensions, geometries and refractive indices will be presented. Thus, we will be able to verify the capacity of this scalar method in predicting light-scattering problems. [ABSTRACT FROM AUTHOR]

Background: Donaldson & Donaldson (2021b) developed a scale to assess Positive Functioning at Work, adding four new blocks to strengthen the original PERMA framework in the workplace. The aim of the present study was to validate this scale in a Spanish sample. Method: 698 Spanish workers participated, 59% were women and 41% were men, 71.6% were employees and 71.2% belonged to the basic worker level. Results: Confirmatory Factor Analysis showed a good fit of the nine-factor model (χ²/df = 2.441; RMSEA = .056, 90% IC (.049, .063); SRMR =. 062; CFI = .926; TLI = .916), the bifactor model (χ²/df = 1.703; RMSEA = .044, 90% CI [.037, .050]; SRMR = .050; CFI = .959; TLI = .952) and the ESEM model (χ²/df = 1.736; RMSEA = .041, 90% CI [.033, .049]; SRMR = .017; CFI = .976; TLI = .942). The adapted scale also demonstrated good internal consistency, with a Cronbach's α of .90 for the scale, and evidence of discriminant, criterion, predictive, and incremental validity with other well-being and performance measures, as well as measurement invariance across educational levels. Conclusions: This scale provides a comprehensive measurement tool that can help in the design of workplace programs and interventions. [ABSTRACT FROM AUTHOR]

Eating disorders have serious physical, mental and social consequences that can affect the quality of life of the sufferer. This study aimed to evaluate the relationship between the severity of ED-related psychopathology and clinical impairment in adolescents with anorexia nervosa (AN) as well as their perception of health-related quality of life. Eighty-six Spanish young women with AN completed a set of questionnaires assessing eating disorder pathology, clinical impairment, and quality of life. The set included the following instruments: the Eating Disorder Examination Questionnaire, Clinical Impairment Assessment, Short Form-12 Item Health Survey, and the Eating Disorder-Specific Heath-Related Quality of Life instrument. Descriptive and regression analyses were applied to identify associations between variables. Higher scores on clinical impairment domains were associated with greater impairment of mental and physical health. Moreover, clinical impairment domains and concerns due to ED were related to a lower quality of life. In conclusion, adolescents with AN have a poor quality of life. Moreover, the findings suggest that the clinical features of impairment may serve as severity indicators of quality of life. [ABSTRACT FROM AUTHOR]

Solution-focused Brief Therapy (SFBT) has generated outcome research worldwide and in a variety of intervention contexts. A systematic literature search yielded 251 published outcome studies on SFBT. SFBT was found superior to control groups or at post-test in almost nine out of every ten studies. Taking only 91 randomized controlled trials (RCTs) into account, SFBT was still found superior in seven out of every ten. Results varied slightly according to intervention type and format, manualization, and components of SFBT. They also varied more according to type of comparator and use of diagnostic criteria. These results widen the evidence base for SFBT. [ABSTRACT FROM AUTHOR]

Interference and diffraction of light are elementary topics in optics. The aim of the work presented here is to develop an accurate and cheap optical-system simulation software that provides a virtual laboratory for studying the effects of propagation in both time and space for the near- and far-field regions. In laboratory sessions, this software can let optical engineering undergraduates simulate many optical systems based on thin slits. The numerical method used is the finite-difference time-domain (FDTD) method that has been successfully applied in many engineering fields. Using this numerical method, the irradiance distribution can be successfully evaluated in different planes far from the simulation grid without degrading performance. In addition, an easy-to-use MATLAB GUI handles all the parameters of the FDTD simulation and computes theoretical values of irradiance for both the Fresnel and Fraunhofer regions. Therefore, by using this software, the student is able to analyze the behavior of the Fresnel and Fraunhofer expressions as a function of the distance. This distance is defined as the space between the slits plane and the plane that contains the virtual screen on which the irradiance pattern is represented. (Contains 1 table and 7 figures.)

We study the recording of complex diffractive elements, such as achromatic lenses, fork gratings or axicons. Using a 3-D diffusion model, previously validated, we are able to predict the behavior of photopolymer during recording. The experimental recording of these complex elements is possible thanks to a new generation spatial light modulator capable of generating periodic and aperiodic profiles. Both experimental and theoretical are analyzed and compared. The results show not only the good response of theoretical model to predict the behavior of the materials, but also the viability of photopolymers to store these kind of elements.