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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.

Holography offers a vital platform for optical information storage and processing, which has a profound impact on many photonic applications, including 3D displays, LiDAR, optical encryption, and artificial intelligence. In this review, we provide a comprehensive overview of optical holography, moving from volume holography based on optically thick holograms to digital holography using ultrathin metasurface holograms in nanophotonics. We review the use of volume holograms for holographic multiplexing through the linear momentum selectivity and other approaches and highlight the emerging use of digital holograms that can be implemented by ultrathin metasurfaces. We will summarize the fabrication of different holographic recording media and digital holograms based on recent advances in flat meta-optics and nanotechnology. We highlight the rapidly developing field of metasurface holography, presenting the use of multi-functional metasurfaces for multiplexing holography in the use of polarization, wavelength, and incident angle of light. In the scope of holographic applications, we will focus on high bandwidth metasurface holograms that offer the strong sensitivity to the orbital angular momentum of light. At the end, we will provide a short summary of this review article and our perspectives on the future development of the vivid holography field.

Abstract Background Invasive fungal disease (IFD) is a significant cause of morbimortality in children under chemotherapy or hematopoietic stem cell transplant (HSCT). The purpose of this study is to describe the changes in the IFD epidemiology that occurred in a Pediatric Hematology-Oncology Unit (PHOU) with an increasing activity over time. Methods Retrospective revision of the medical records of children (from 6 months to 18 years old) diagnosed with IFD in the PHOU of a tertiary hospital in Madrid (Spain), between 2006 and 2019. IFD definitions were performed according to the EORTC revised criteria. Prevalence, epidemiological, diagnostic and therapeutic parameters were described. Comparative analyses were conducted using Chi-square, Mann-Whitney and Kruskal-Wallis tests, according to three time periods, the type of infection (yeast vs mold infections) and the outcome. Results Twenty-eight episodes of IFD occurred in 27 out of 471 children at risk (50% males; median age of 9.8 years old, [IQR 4.9-15.1]), resulting in an overall global prevalence of 5.9%. Five episodes of candidemia and 23 bronchopulmonary mold diseases were registered. Six (21.4%), eight (28.6%) and 14 (50%) episodes met criteria for proven, probable and possible IFD, respectively. 71.4% of patients had a breakthrough infection, 28.6% required intensive care and 21.4% died during treatment. Over time, bronchopulmonary mold infections and breakthrough IFD increased (p=0.002 and p=0.012, respectively), occurring in children with more IFD host factors (p=0.028) and high-risk underlying disorders (p=0.012). A 64% increase in the number of admissions in the PHOU (p

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.

Low-toxicity solar concentrator systems represent an important challenge for outstanding photovoltaic (PV) applications. Particularly, multiplexed holographic lenses (MHL) as Holographic Solar Concentrators (HSC) provide insight into promising possibilities for Building-Integrated Concentrating PVs. This technology does not affect crucial ecosystems, and can convert buildings from energy consumers into energy suppliers. They can be used in windows, roofs, or walls, and a high diffraction efficiency and wide acceptance angle are desired. In this work, we presented several designs of MHL of low spatial frequency 525 lines mm ^−1 , based on a low-toxicity photopolymer and supported on a window glass. The average diffraction efficiency of these HSC was evaluated at 633 nm, whereas the acceptance angle was evaluated by measuring the short-circuit current under solar illumination at different incident angles. Versatile and high-efficiency holographic elements have been used to concentrate sunlight from different relative positions during the day, avoiding the need for expensive tracking systems. To the best of our knowledge, this is the best trade-off between high diffraction efficiency (85 $\%$ ) and wide acceptance angle (104 ^∘ ) in a low-toxicity holographic solar concentrator.

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]

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.