Speckles are a statistical interference phenomenon which arises when coherent light is scattered by an optically rough surface. The resulting speckle field can be examined using statistical techniques and some results that arise are related to the form of the resulting speckles. Characteristic features are the so-called lateral and longitudinal speckle size as well as the orientation of speckles in the z-direction. It has been shown that the 3D orientation of speckles in free-space and in Fourier transforming systems are different from each other. Here we review some of Sheridan's work in this area. We first examine the speckle field formed by a diffuser in free space over a 3D volume. Next an Optical Fourier Transform (OFT) system is assumed, where the diffuser is placed in the front focal length of a Fourier transforming lens and we examine the resulting speckle field in the back focal plane of this OFT system. We compare and contrast the properties of the speckles from both setups free-space and Fourier.

In this paper we investigate the use of two similar photosensitive dyes that are used in the creation of photosensitive polymers. The specific dyes are what makes the photopolymer material responsive to specific wavelength that the polymer material is exposed to. The subsequent self-written waveguides (SWW) that are created are a product of this interaction between the light beam, photopolymer material and the sensitive dye. We investigate the optical characteristics and light propagation comparisons between the two dyes and the their photosensitive response associated with specific wavelengths.

Polarization holography is a newly researched field, that has gained traction with the development of tensor theory. It primarily focuses on the interaction between polarization waves and photosensitive materials. The extraordinary capabilities in modulating the amplitude, phase, and polarization of light have resulted in several new applications, such as holographic data storage technology, polarization multiplexing, vector or vortex beams, and optical functional devices. In this paper, fundamental research on polarization holography with linear polarized light, a component of the theory of polarization holography, has been reviewed. Primarily, the effect of various polarization changes on the linear and nonlinear polarization characteristics of reconstructed light wave under continuous exposure and during holographic recording and reconstruction have been focused upon. The polarization modulation realized using these polarization characteristics exhibits unusual functionalities, rendering polarization holography as an attractive research topic in many fields of applications.

The see-through application of holographic optical elements (HOEs) has gained a lot of attention in the scientific literature in recent years. Regarding this kind of holograms recorded in photopolymers, the shrinkage plays an important role in the final properties of the display, as it may alter the Bragg angle. The present work is focused on the characterization of a HOE as a coupler in a waveguide combiner, recorded in holographic transmission geometry without prisms in the experimental set-up. From this point of view, it has been found that for specific geometries where the diffracted beam cannot be trapped a priori, a significant coupling effect exists: this variation in the diffracted energy and the propagation angle inside the glass can be used to measure the shrinkage of the photopolymer for this HOEs recording.

We present new experimental and fitting methods that describe Bragg selectivity of distorted holograms in soft photopolymers. These are used to study the mechanical response of holograms that shrink when exposed. An inelastic response is identified which can be exploited to reduce fringe distortion even in the presence of shrinkage.

Photopolymers are special polymeric materials that can be irradiated with light to form polymer structures. It is widely used in the fields of 3D printing, anti-counterfeiting and information storage. In today's relatively mature holographic storage technology, high-density volume holographic data storage requires storage materials with a high response rate, high effective storage density and optical transparency, and high signal-to-noise ratio, etc. For this reason, storage materials have been studied in various fields. Phenanthrenequinone (PQ)/poly(methyl methacrylate) (PMMA) materials are a choice for holographic storage. By modifying the polymer substrate of the lamellar PQ/PMMA holographic polymeric material, it is possible to reduce the generation of bubbles during the preparation of the material to increase the usable area of the material, and at the same time, it is also possible to improve the photoreceptor sensitivity to a certain extent, to increase the read/write speed of the material and to analyze the causes of the phenomenon using the first nature principle calculations.

Bayfol^® HX photopolymer films prove themselves as easy-to-process recording materials for volume holographic optical elements (vHOEs) and are available in customized grade at industrial scale. Their full-color (RGB) recording and replay capabilities are two of their major advantages. Moreover, the adjustable diffraction efficiency, tunable angular and spectral selectivity of vHOEs recorded into Bayfol^® HX as well as their unmatched optical clarity enables superior invisible “off Bragg” optical functionality. As a film product, the replication of vHOEs in Bayfol^® HX can be carried out in a highly cost-efficient and purely photonic roll-to-roll (R2R) process. Utilizing thermoplastic substrates, Bayfol^® HX was demonstrated to be compatible to state-of-the-art plastic processing techniques like thermoforming, film insert molding and casting, which opened up using a variety of industry-proven integration technologies for vHOEs. Therefore, Bayfol^® HX makes its way in applications in the field of augmented reality such as Head-up-Displays (HUD) and Head-mounted-Displays (HMD), in free-space combiners, in plastic optical waveguides, and in transparent screens. Also, vHOEs made from Bayfol^® HX are utilized in highly sophisticated spectrometers in astronomy as well as in narrow band notch filters for eyeglasses against laser strikes and retail optics. See through applications such as, HMD and HUD, have demanding performance requirements on combiner and imaging technologies such as efficiency, optical function, and clarity. The properties of Bayfol^® HX make it principally well suited to solve these challenges in primary display, and near-infrared imaging applications such as eye-tracking. Based on a customizable and available toolbox, Bayfol^® HX can be adopted for a variety of such applications. To serve further sensing applications we recently extended our chemical toolbox to address the photo sensitization beyond RGB into the Near Infrared Region (NIR), and reported already on various demonstration examples. On our way to generate a standardized Bayfol^® HX film sensitized in the NIR - comparable to Bayfol^® HX200 sensitized for RGB - we investigated the initiation mechanism in greater detail for this tailored NIR photoinitiation system and report on the performance characteristics of the envisaged standardized NIR sensitized Bayfol^® HX film fabricated on the production coating line.

An azo-functionalized copolymer derived from Poly (CACzE-MMA), CACzE, and DPP in is introduced as an innovative material to address challenges in vectorial holography. This copolymer surpasses existing materials by achieving a maximum diffraction efficiency of 85%, retaining holographic information for over 30 days, and allowing for fast writing at low intensity. By utilizing the copolymer's re-writability, polarization-angular multiplexing, and hybrid polarization-spatial multiplexing techniques are successfully implemented, which enables recording multiple images without significant crosstalk. This advancement has significant implications for holographic technology, expanding its applications in data storage, imaging, and display systems.

The progress of space based scientific research leads to an increasing demand for more efficient and less bulky instruments. Conventional refractive elements make up a critical part of many optical instruments launched into space; however, they can be bulky and heavy. Holographic optical elements are an efficient alternative to replace the conventional optical elements as they are lightweight and can be miniaturized. Current materials typically used for volume holographic optical elements are not robust enough for use in space environment. Recently a promising photopolymerisable glass has been developed using a sol-gel technique, which can provide dry layers suitable for holographic recording with a significantly lower curing time. In addition, the material has shown stability after exposure to high humidity and temperatures up to 130°C. However, its UV resistance needs to be improved in order to satisfy the requirements for application in space. The main goal of this work is to study and improve the UV resistance of the photopolymerisable glass. The following approaches have been used: 1) post-recording exposure to uniform laser beam and 2) modification of the material composition. It was found that exposing the material to a uniform beam immediately after the recording improves UV resistance and provides stability of the layer. The effect of the chemical composition of the material on its UV resistance was also studied by varying the concentration of the dye and adding Polyurethane Diol to improve its elastic properties. The performance of the material was tested by studying the optical properties of transmission gratings recorded in the layers, such as diffraction efficiency and refractive index modulation, before and after UV exposure. The first experimental results for both approaches have shown promising results and the potential routes for further developments have been identified.

A subwavelength structure made of a resonant waveguide grating embedded in a luminescent sol-gel layer enables a dual color effect. The resonant waveguide grating consists of a diffraction grating and a high refractive index guiding layer using a TiO₂ based sol-gel with a higher refractive index (n_g = 2.2) than its silica sol-gel surroundings (n_s=1.5). The resonant waveguide grating is designed to achieve visible resonant reflection of TE polarized incident waves in the green color spectrum. The resonant structure is then coated with a thick layer of silicone doped with a luminescent material of formulation Y₂O₂S:Eu³⁺. This latter leads to emission in the red domain under UV excitation. This quasi-symmetric structure is transparent in the visible range for observing the various phenomena. Nano-imprint technology is used for the fabrication of the grating on the sol gel layer to demonstrate its fabrication potential. Therefore, it is a low-cost fabrication technique used to replicate the microstructure, which can be up scaled for industrial applications. Preliminary results will be presented at the conference, covering modelling through the design of the optimized microstructures. Experimental results will be showcased with first demonstrators comprising Nanoimprinted sol-gel layers with a resonant waveguide grating and a luminescent layer. Experimental measurements will be carried out to characterise both the optical performance of the luminescent coating and the resonant waveguide grating.

Metasurfaces (MSs), structures which are tailored artificial arrays of metallic or dielectric nanostructures, are a promising approach for controlling light propagation and its properties, like amplitude and/or phase distribution in space. Active (or tunable) MSs allow to control light not only in space, but also in time. One strategy to achieve tunability of MSs is to use phase change materials (PCMs), like vanadium dioxide (VO₂), among their constituents. By changing a critical parameter, as temperature, the PCM dielectric function suffers drastic variations, which may strongly alter the MS’s light extinction properties. Two kinds of specially designed MSs employing VO₂ are discussed in this work. One, fully composed of VO₂ nanodisks on a glass substrate, presents Mie resonances in the visible while the other, composed of pairs of tilted elliptical pillars made from Si supporting a thin layer of VO₂ capped by SiO₂, show quasi-Bound States in the Continuum resonances in the Mid-IR. We demonstrate that these resonances can be continuously modulated in their amplitude by factors of at least ~3 dB, representing a relevant approach for dynamically controlling light-matter interaction on nanoscale.

Unique structural features of metal-organic frameworks such as their organic-inorganic nature, coupled with a series of weak and strong chemical interactions, provide these hierarchical materials with an adaptive response to external stimuli (including light). The latter allows one to demonstrate energy-efficient and ultra-fast optical processes for light generation, conversion, triggering, encryption, absorption, and transition. Covering the current state and perspectives in this new field of material science for photonics, the report aims to develop a deep understanding of the interaction of light with such hierarchical materials to create sustainable and energy efficient optical devices.

This work analyzes the piezophototronic effect in zinc oxide (ZnO) thin films deposited by a physical vapour deposition (PVD) technique, studying changes in the piezoelectric coefficient (d₃₃) as a function of ultraviolet (UV) light radiation. The piezophototronic effect comprises the coupling of piezoelectricity, semiconductor behaviour and photoexcitation in piezoelectric materials. This effect has been conventionally studied in piezoelectric thin films subjected to an external mechanical stress, where the piezo-charges generated by the mechanical stress induced at both ends of the piezoelectric material, are able to control the piezo-potential of electric contacts or energy levels in p-n junctions. In this regard, the external stress applied to a piezoelectric material is able to control the process of carrier injection, transport and recombination, allowing the improvement of the efficiency in optoelectronic devices. However, the study of the piezoelectric properties of thin film materials, such as ZnO, as a function of light exposure has not been explored yet. This work presents a thorough analysis on the d₃₃ of ZnO thin films measured by quasi-static or Berlincourt method as a function of the excitation UV light conditions. Structural, optical and electrical properties of the films were also analyzed. This work also covers the exploration of this new piezophototronic device as an active layer in sensing platforms and energy harvesting devices.

Low-weight, passive, thermal-adaptive radiation technologies are needed to maintain an operable temperature for spacecraft while they experience various energy fluxes. Vanadium dioxide (VO₂) is a commonly used dynamic response material that can transition from a low emissivity (insulating) state to a high emissivity (radiating) state near room temperature. In this study, we used a thin-film coating with the Fabry-Perot (FP) effect to enhance emissivity contrast (Δε) between the VO₂ phase-change states. This coating utilizes a novel hybrid material architecture that combines VO₂ with the mid- and long-wave infrared transparent chalcogenide, zinc sulfide (ZnS) as a cavity spacer layer. We simulated the design parameter space to obtain a theoretical maximum Δε of 0.63 and grew a prototype device. Using x-ray diffraction, Raman spectroscopy, and Fourier Transform Infrared (FTIR) Spectroscopy, we determined that an intermediate buffer layer of TiO₂ is necessary to execute the polycrystalline growth of VO₂ on ZnS. We optically characterized the pulsed laser deposition grown VO₂ and ZnS using IR-spectroscopic ellipsometry. Through measuring the temperature-dependent FTIR spectroscopy, our prototype sample demonstrated FP-cavity enhanced adaptive thermal emittance.

Optical microscopic techniques are the most commonly used methods in biology and medical research. In recent years, structured light plays vital roles to enhance resolution. In addition, metasurfaces, the emerging optical techniques, with unique optical capabilities to manipulate the basic characteristics of light have received a significant amount of interest in the optical microscopic field. This talk will introduce the latest studies on the biomedical use of structured light, as well as metasurface. The following are the topics that will be covered: quantitative cell imaging, optical sectioning microscopy; light sheet microscopy; and optical tweezers. This talk will also discuss the technological challenges presently encountered with metasurface from the point of view of preclinical and clinical systems.

Flat patterned surfaces, traditionally realized through lithographic techniques, can manipulate the wavefront of light within minimal thicknesses comparable to the wavelength of light, offering significant potential for advances in science and technology. Amorphous polymers containing azobenzene molecules introduce a revolutionary approach to the direct fabrication of reprogrammable flat optical devices. In my work, I use azopolymers in combination with digital holographic illumination to enable maskless and reversible surface patterning. This innovative approach allows the design and the fabrication of reconfigurable optical elements, where light is used to fabricate the device, to tune its functionality or even completely reprogram it while the optical component is still maintained aligned in an operational setup.

In confocal microscopy, multifocal illumination can reduce image capture time compared to single point scanning. However, due to increased system complexity, attaining uniform multifocal illumination across the field of view with traditional approaches is difficult. For multifocal confocal imaging in lateral as well as in axial directions, we propose two methods using a volume holographic lenslet array illuminator (VHLAI) and a volume holographic axial multi-plane illuminator (VHAMI) respectively. A super Gaussian (SG) beam shaping was incorporated with VHLAI with a 43% efficiency and utilized in a confocal microscope to provide uniform array illumination. Multiplexed holographic gratings are used to achieve simultaneous multi-plane illumination. Multiple photo detector arrangements have been done to carry out simultaneous multi-plane imaging without mechanical or electro-optic axial scanning. The design methodologies for photopolymer-based volume holographic beam shapers are discussed, as well as their benefits. we demonstrate the ability of proposed approaches by comparing optically sectioned microscopic images of fluorescence beads, florescence pollen grains, and biological specimens to wide-field images. The proposed systems can greatly reduce image acquisition time while maintaining image quality. When compared to former spatial light modulating devices, the illumination approach employed in our confocal systems are more direct and compact. Multifocal illumination may considerably shorten scanning time without requiring a change in scanning devices, while also providing uniform illumination across the field of view. These multifocal confocal systems construct images more quickly while requiring no modifications to scanning hardware. The approaches shown here might be useful in high-speed multifocal microscopy platforms.

Here we present a method of creating GRIN optical components with custom refractive index profile through layerless 3D patterning of diffusion-driven photopolymer. We show 3D control over a stable refractive index profile, and through post-processing, tune the resulting mechanical properties of the lens for various applications.

Photosensitive materials with ever-improving properties are of great importance for optical and photonics applications. Additionally, they are extremely useful for designing components for neutron optical devices. We provide an overview on materials that have been tested and successfully used to control beams of cold and very cold neutrons based on diffractive elements. Artificial gratings are generated and optimized for the specific application in mind. We discuss the needs of the neutron optics community and highlight the progress obtained during the last decade. Materials that have been employed so far along with their properties are summarized, outlining the most promising candidates for the construction of an interferometer for very cold neutrons.

Volatile organic compounds (VOCs) are analytes of increasing interest due to the risks they pose to human health in terms of cardiovascular and carcinogenic complications. Current state of the art VOC detectors includes MEMS and semiconductor type sensors which suffer from cross sensitivity, drift, and poor selectivity between VOCs. Furthermore, these devices often require complex and costly fabrication and readout techniques. Holographic sensors based on various types of diffractive structures have been demonstrated previously as highly sensitive, robust, and versatile sensing devices for numerous analytes including temperature, humidity and VOCs, with simple and low-cost fabrication and operation characteristics. It has also been demonstrated that the sensitivity of the holographic structures can be enhanced through coupling into an optomechanical configuration, however this coupling was only investigated for unslanted volume transmission gratings. In this work, the sensitivity of a range of structures fabricated using holographic recording techniques is investigated. The response of volume transmission holographic gratings is studied in three different configurations – fixed gratings on glass slides, optomechanical holographic cantilever and optomechanical holographic membrane. The samples are tested in a vacuum chamber for response to air with the view to optimizing the most sensitive platform as a highly accurate VOC detector. The results further validate that the coupling of volume transmission holographic gratings with a mechanical transducing method enhances sensitivity. Furthermore, the study demonstrates that the membrane configuration has the potential to provide the most sensitive, stable, and repeatable sensing platform of the three presented.

Nowadays, one of the challenges in obtaining competitive photovoltaics is to achieve lightweight, low-cost, and free-tracking systems. It is also desired to eliminate wavelengths that can damage the photovoltaic cell by overheating. To this end, volume holographic lenses (HLs) allow controlling the solar radiation that hits the photocell, avoiding harmful radiation that can damage photocells, such as infrared radiation, which heats the solar cells, but does not efficiently convert solar energy into electrical energy. In addition, holographic solar concentrators based on multiplexed HLs have the advantage that they do not require any solar tracker. In this work, we present the optimization of the relevant conditions in the fabrication of multiplexed HLs stored in Biophotopol. These parameters refer to both the material factors (optimal concentrations of dye and monomer, thickness) and the optical recording factors (optimal number of multiplexed HLs, angular distance peak-to-peak, and exposure times). Finally, a theoretical study of the exposure times has been done using the exposure schedule method (ESM) to improve the average diffraction efficiency.

In the study of surface relief based diffractive sensors, surface morphology is a key parameter. There are many approaches to patterning of surfaces on the micro and nanoscale, such as lithography, self-assembly, ultra-thin alumina mask nano-surface patterning, and Scanning probe techniques. While these techniques allow for fabrication of structures with very high resolution, the development of an alternative technique that can deliver complex, easily customisable surface structures at a low cost is well justified. Two optical techniques for patterning of photopolymers of different chemical compositions will be presented and compared. They allow the fabrication of surface structures on the micron scale directly into a photopolymer layer by single step recording of the whole pattern. The first approach utilizes holographic recording with three laser beams with different states of polarization and adjusted intensities. A semi-automated optical system utilising this approach currently allows for the creation of surface relief cross-gratings (SRCG) of unit cell size ranging from 8 x 8 μm2 to as small as 2 x 2 μm2, but smaller features are theoretically possible. Control over surface morphology and surface roughness by optical patterning is experimentally confirmed. The second approach involves the use of a digital micro-mirror array spatial light modulator. This approach allows for the creation of surface relief with features as small as 3 μm2, with higher achievable image complexity, due to the control over individual micro-mirrors. Surfaces fabricated in photopolymer materials utilising both approaches were characterised via atomic force microscopy, phase contrast microscopy, fast Fourier transform analysis of collected images, and diffraction efficiency measurements. Both approaches are compared in view of their application in diffractive optical sensors.

Simple photopolymer based on pentaerythritol tetrakis [3-mercaptopropionate] (PETMP) dispersed in Cellulose Acetate Butyrate (CAB) binder is developed to make surface and volume phase patterns transferred by means of a Direct Laser Writing (DLW) using 405nm laser. 1D and 2D gratings, as well as complex Computer Generated Holograms (CGHs) are printed and fully characterized exploiting different imaging techniques, including digital holography to highlight the contribution of surface phase shift and volume phase shift. Moreover, the diffraction efficiency of gratings is measured and correlated to the writing conditions.

This study introduces novel holographic diffuser applications employing acrylamide- or diacetone acrylamide-based photopolymers, patterned within the volume on a micron scale by a single-beam holographic recording process. These diffusers have previously been presented as potential treatments for amblyopia and diplopia. This work has now been extended to spectrometric analysis to determine their properties under broadband light. Diffusive elements with higher diffusion efficiencies exhibited a marginal reduction (< 5%) in diffusion efficiency across most of the visible spectrum. Given the intended application of these holographic diffusers, cytotoxicity assessments were also performed. This is significant as there is a difference in toxicity between the crystalline acrylamide (classified as a category 3 material) and diacetone acrylamide (classified as a category 4 material). The findings indicated substantially lower toxicity in holograms produced with diacetone acrylamide-based photopolymer. The accelerated ageing of both formulations of holographic diffusers indicated that the acrylamide-based holographic diffusers did not reduce efficacy in the 292 days of ageing. The diacetone acrylamide-based holographic diffusers exhibited reduced efficacy by day 182. Despite this, both formulations have been shown to perform for prolonged periods as the treatment modality would require. These results emphasise that holographic diffusers exhibit minimal spectral impact, and longevity on the scale of treatment regimes which are crucial considerations for their prospective use case as treatments for amblyopia and diplopia.

A photopolymerizable nanoparticle-polymer composite (NPC) is a novel nanocomposite photopolymer that is dispersed with inorganic nanoparticles having a large refractive-index difference from that of the formed polymer. In order to realize the uniform and high dispersion of nanoparticles without any aggregation, we employ nanostructured polymers that possess highly branched main chains, the so-called hyperbranched polymer (HBP), as size and refractive-index controllable organic nanoparticles with its ultrahigh refractive index. We show that high dispersion of the ultrahigh refractive index HBP in a photopolymerizable NPC provides a volume holographic grating possessing the saturated refractive modulation amplitude as large as 0.03 at grating spacing of 0.5-μm in all the visible spectral regions of the red (640nm), the green (532nm) and the blue (405nm). Such a high contrast volume holographic grating can be used for volume optical holographic elements in a wearable headset for augmented and mixed reality.

The imperative for monitoring volatile organic compounds (VOCs) emerges from their harmful impact on human health when inhaled excessively over a long term. Polydimethylsiloxane (PDMS), valued for its transparency and excellent flexibility, has already been demonstrated as a promising biocompatible and cost-effective transducer for optical VOCs sensing. Moreover, it facilitates further functionalisation with adsorbing materials to enhance sensitivity and selectivity for specific VOCs detection. We fabricated and examined PDMS-based surface diffraction gratings after exposure to selected VOCs, demonstrating different response for polar and non-polar molecules. Investigated gratings were prepared by replicating sinusoidal surface relief structures inscribed in acrylamide photopolymer using a holographic recording method. Our study is primarily concerned with gratings featuring a period of 8.4 ± 0.2 micrometres and an amplitude of 585 ± 32 nanometres. The proposed sensing method relies on diffraction efficiency modulations induced by the analyte causing a dimensional change in the PDMS layer and altering its refractive index by filling its pores. Here, we delve deeper into the intrinsic properties of PDMS that influence diffraction efficiency when the surrounding temperature is varied. Any temperature sensitivity may significantly impact the response of the grating to VOCs in a thermally unstable environment. The implications of this study are particularly important for sensor applications for air quality monitoring, as they are susceptible to variations stemming from seasonal influences throughout the year. The variation of the diffraction efficiency of the surface relief PDMS gratings was studied in the temperature range 20 to 60 °C. It was observed that diffraction efficiency alters with the amplitude of diffraction efficiency change in the range of 0.08-0.42%.

Devices based on liquid crystal (LC) exhibit a great interest in Optics due to their capability to set up applications with variable properties. Some examples of these elements are spatial light modulators (SLM) based on parallel-aligned liquid crystal on silicon (PA-LCoS) microdisplays. Other applications of LC in diffractive elements are based on polymer-dispersed liquid crystal devices (H-PDLC), e.g. diffraction lenses, optical data storage, and image capture devices. These examples share one of the most exciting features of LC, which is the capability to change the optical properties with an external voltage. Here, a review of the latest developments in estimating the director distribution in LC-based devices is summarised. The results here summarised show the potential of the approach for rigorously analysing the fringing field and crosstalk polarimetric impact on PA-LCoS devices, the bending in H-PDLC fringes, and the application of machine learning on the estimation of the LC director distribution in this kind of devices.

Coaxial- and counter-optical setups for laser ultrasonics using a photorefractive liquid crystal were fabricated. In laser ultrasonics, an object is irradiated with a laser pulse to create an ultrasonic vibration, and then another laser beam is used to detect the vibration. The phase of the laser beam reflected from the object is shifted by the ultrasonic vibration. By using liquid crystals with photorefractive properties, the resulting phase shift of the laser beam reflected from the material can be detected. Compared to traditional laser ultrasonic methods, this system offers a simpler optical setup and allows for more accurate measurements that are not affected by environmental vibrations.

It is well known that Spatial Light Modulators (SLM) are of great interest and used in many different areas because of their continuous capability of light modulation and their potential as a linear variable retarder. However, high-definition SLM devices face the challenge of providing high performance under the influence of different phenomena, such as crosstalk between adjacent pixels, fringing fields, and diffraction effects arising from the finite pixel grid pattern. In this work, a numerical analysis that computes the director orientation as a function of the retardance across specific voltages (gray level) is compared to experimental results. More specifically, this work is focused on analysing how previously mentioned phenomena affect the interpretation of the residual twist angle in parallel-aligned (PA) on SLM. This twist angle is computed from the Stokes parameter and compared to the actual orientation of the director distribution.

Typically, a 360º phase-shift is required to implement diffractive optical elements (DOEs) in modern photonics applications. However, the possibility of showing much larger phase-shifts is a very appealing property which provides additional degrees of freedom to produce multiplexed functions onto DOEs. On the other hand, modern liquid crystal on silicon devices (LCoS) add real-time programmability to the functionality of the DOE displayed, but this has been typically demonstrated by parallel-aligned LCoS (PA-LCoS) devices. We show programmable DOEs produced using vertically-aligned LCoS (VA-LCoS) devices, with a phase-shift range largely exceeding 360º. We show some results dealing with blazed gratings and on the analysis of their higher diffraction orders, validating their use for multiorder diffractive optical elements.

Quantum dots (QDs) with favorable optical properties have been synthesized and developed in recent decades, although most are based on a toxic metal system – cadmium selenide. InP-based QDs were studied as alternatives to replace the toxic Cd-based QDs. However, the synthesis of InP-based QDs relied on air-sensitive phosphine precursors, making the synthesis route more challenging. In our project, we initially substituted the phosphine precursor with phosphinecarboxamide, which is air-stable. This modification allowed for a one-pot reaction, streamlining the synthesis route. The colour of the synthesized InZnP/ZnS QDs was tuneable from visible green to red, with the emission wavelength ranging from 510 to 620 nm by adjusting the degassing time. Additionally, several phase transfer processes were undertaken to make the InZnP/ZnS QDs water-soluble, followed by cell imaging on Euglena cells and HeLa cells, proving the potential application of the QDs in bioimaging.

The bromide (Br) ions on a conjugated polyelectrolyte (CPE) PFN-Br were converted to tetrafluoroborate (BF₄) or hexafluorophosphate (PF₆) ions through anion exchange to obtain two polymers PFN-BF₄ or PFN-PF₆ for surface engineering of zinc oxide nanocrystals (ZnO NCs). The ionic groups on CPEs can form permanent dipoles to facilitate charge injection from ZnO NCs to cesium lead bromide (CsPbBr₃) NCs emitters and therefore promote luminescent properties of inverted perovskite light-emitting diodes (PeLEDs). The incorporation of CPEs also helped to passivate the defects of ZnO NCs films, improve contact between ZnO and perovskite layers, and prolong carrier lifetime of CsPbBr₃ NCs. PeLEDs based on different CPEs were fabricated and evaluated.

Up-conversion photoluminescence (UCPL) is an optical process in which the electrons from ground state absorb lower energy photon (NIR and/or IR) to excite to the excited state and the electrons will return to the ground state while emitting higher energy photon (UV and/or Visible light). However, the occurrence of UCPL in carbon-based nanomaterials was rare to be found. Herein, we provide better understanding and confirmation to the phenomenon of UCPL in graphene quantum dots (GQDs). From excitation-dependent PL measurement, it shows that GQDs have excitation-independent PL emission. Furthermore, the PL emission can still be observed even when it was excited using low energy photons, confirming the phenomenon of UCPL. We performed temperature-dependent PL measurement to further confirm the credibility of UCPL phenomenon. It showed that as increasing temperature, the UCPL intensity grows higher, showing the contribution of phonon in UCPL process. Therefore, we confirm the UCPL phenomenon and due the phonon contribution in the process, we conclude that anti-Stokes photoluminescence (ASPL) is the UCPL process in our materials.

In this work, optical and structural properties of three-dimensional graphene (Gii^TM) foam have been analysed to validate the potential of this material as an active layer in broadband optoelectronic devices. The chemical structure of Gii^TM foam was characterized by Raman spectroscopy carried out at different wavelengths (455, 532, 644, and 780nm) and laser powers (1 to 8mW). In this study, two types of Gii^TM foam were analysed, including standard graphene (ST-Gii), and low resistance graphene (LR-Gii) whose main difference is the defects-density modulating their electric conductivity. The performance of both ST-Gii and LR-Gii was determined by examining intensity and position, of G, D, and 2D peaks as a function of light source conditions (i.e., wavelength and power). Results demonstrate that ST-Gii presents a 1.37 G/D intensity ratio, which is 0.2 lower than that observed in LR-Gii, evidencing the drastic change in the electronic properties of both materials obtained during the synthesis process. Moreover, the study of the materials as a function of the wavelength showed – in the case of ST-Gii material – a clear ‘optical switch’ behaviour from G/D of 1.37 to 0.79 when the material is irradiated with light below and above 532nm, respectively. This interesting result indicates that Gii^TM could be a potential candidate for optoelectronic devices (phototransistors, photodiodes, and photodetectors), thanks to the modulation of its electronic properties by irradiating the material to different light wavelengths. To further investigate this effect, in this work, we present the concept of a photo-resistive detector based on ST-Gii.

Photocathodes as photoelectric conversion materials play a key role in vacuum photodetectors, accelerator-based light sources, and ultrafast electron microscopy. Since graphene has unique properties such as gas impermeability, electron transparency, a large specific surface area, and atomic thinness, the graphene/metal van der Waals heterojunction material may provide the possibility to improve the photoemission performance of metal photocathodes through surface modification. The specific Cs/O activation process was performed on the surface of graphene/copper heterojunction material. Its photoemission behaviors, including light-excited current, spectral response, and degradation characteristic, were investigated to verify the effect of surface modification on the improvement of photoemission performance. The experimental results show that, by preliminary Cs/O activation, the graphene/Cu photocathode can extend the threshold of spectral response to the near-infrared region. Furthermore, through repeated Cs/O activation, the cathode sample can possess better stability of operation. The photoelectron spectroscopy measurement results present the changes in the chemical states of surface elements and the corresponding work function after Cs/O activation and degradation. This Cs/O-activated graphene/metal photocathode can provide a new strategy to enhance the photoemission performance and stability of such photocathodes.

The introduction of a mathematical sequence into a diffractive lens phase, such as the Fibonacci or Silver Mean Sequence, allows us to achieve multifocal behavior in the Fresnel regime. This study explores the use of photopolymers based on Polyvinyl Alcohol Acrylamide (PVA/AA) as an optical recording medium for these complex lenses. PVA/AA photopolymers were selected because of their versatility and good response in recording DOEs. Moreover, the use of a 4F optical system configuration and a Spatial Light Modulator (SLM) provides the flexibility to adjust lens radius and orders, enabling the creation of lenses with adaptable focal lengths and specific sizes. In addition, we model the material’s behavior using a 3D diffusion model with a coverplate and index matching, allow us to adjust some parameters to obtain higher diffraction efficiency. These lenses find practical applications in microscopy and ophthalmology, particularly as progressive intraocular lenses. Their ability to adjust focal points and sizes makes them invaluable for addressing vision problems, like presbyopia and enhancing optical devices used in medical and research settings.

Estimating the actual parameters of real holographic volume gratings from diffraction efficiency measurements is challenging. The natural formation of the grating provides different phenomena, such as shrinkage, bending of the fringes, or non-homogeneous modulation as a function of the thickness, amongst other issues. This work proposes a deep learning Convolutional Neural Networks (CNNs) and Feedforward Neural Networks (FNNs) hybrid architecture capable of predicting the grating parameters from theoretical and experimental diffraction efficiency patterns. For the training set of this regression problem, Kogelnik’s Coupled Wave Theory simulated data has been employed. Our best model has been trained with an 8000-sized dataset of 80 points of diffraction efficiency patterns simulated from a range of values for the normalized grating wavelengths, index modulations, and optical depths. It achieves test losses under one per cent (mean absolute error) for predicting the normalized grating wavelengths, index modulations and optical depths.

In this work, reflection gratings has been stored in Bayfol X200 from Covestro. Up to two high-efficiency reflection holograms have been multiplexed in the same layer due to the physical thickness of the material films, 16μm. The less material thickness, the fewer number of high diffraction efficiency multiplexed holograms we can store in it. Once multiplexed the pairs of holograms at different recording angles we have stuck several layers together, forming a multilayer system. From this multilayer system, we have obtained a wide diffracted spectrum were the result is the superposition of all the multiplexed gratings recorded in each layer. Therefore, this system has a good chromatic selectivity and allows us to select the reflected wavelengths and the spectral wide for each application.

The development of new holographic materials represents a field of research in continuous evolution. The design and synthesis strategy of these materials must respond to the desirable characteristics of the photonic devices that need to be manufactured. Hydrogels are used as binders in applications in which the material must retain its structural integrity in liquid media. In applications where it is required to store volume holograms in hydrogels, it is necessary to carry out a first incubation process in solutions containing the necessary components. The general aim of this work has been to optimize the composition of incubator solutions composed of acrylamide as monomer, N,N′-methylenebis(acrylamide) as crosslinker, triethanolamine and yellow eosin as photoinitiator system and DMSO/water as solvent. The effect of varying the monomer and crosslinker on the diffraction efficiency of stored holograms has been investigated.

This study explores the application of GABA-functionalized silver nanoparticles (GABAAgNPs) in nanopriming, a technique used to improve seed germination, accelerate seedling growth, and enhance plant stress tolerance. GABAAgNPs were characterized using diverse techniques, including UV-Vis, FTIR, XRD, TEM, Zeta potential, and DLS. Scanning electron microscopy (SEM) was also used to analyze the seed coat and fluorescence spectroscopy to map chlorophyll content in seedlings and nanoparticle toxicity. The results revealed the ability of GABAAgNPs to induce pore formation in the seed coat, facilitating water uptake and triggering germination processes. Furthermore, the investigation revealed that GABA undergoes metabolism within plant cells, generating glutamate. This glutamate serves as a precursor for the synthesis of aminolevulinic acid (ALA), which ultimately contributes to chlorophyll production, as evidenced by the increased vigor index and improved chlorophyll fluorescence. This work demonstrates the potential of GABAAgNPs as a novel and promising approach to promote seed germination and enhance plant resilience in sunflowers.

This paper provides a broad overview of historical and current developments of holographic lenses (HLs) in concentrating solar power. The review focuses on the recording material typically employed for HLs in concentrating solar photovoltaic and/or concentrating solar thermal collectors. This review shows that the use of HLs for energy transformation, achieves high performance efficiency in the designed physical systems, furthermore, some important elements to consider for future designs are presented, especially those related to the etching material of the HLs. Finally, the article outlines future recommendations, emphasizing potential research opportunities and challenges for researchers entering the field of photovoltaic and/or concentrating solar thermal collectors based on HLs.

The structural transformations (STs) in metal-organic frameworks (MOFs) have routed a promising possibilities to use them for data processing and information encoding. However, in order to be applicable in real life devices, such systems encounter a problem of low speed rates (κ) and poor repeatability. In our research, we report on a flexible 2D MOF single crystals possessing light driven structural anisotropy with fast (5000 s^-1) and highly repeatable (over 10⁴ cycles of ST at ambient conditions) optical modulation. The confirmed stability of such MOF-based optical modulator during 1 year shed light on the design of new family of functional optical materials for information technology.

Direct laser writing (DLW) is an industry-oriented method for creating the images both on the surface and in the volume of various media for nanophotonic, medicine, bioengineering, and even IT applications. However, the challenges on the creation of color images with sub-diffraction resolution inside the media, as well as the impossibility of achieving black and grayscale shades simultaneously with full color palette significantly hinder the widespread use of DLW. Staying in the laser writing paradigm, we have proposed a new concept for simultaneous multicolor and grayscale writing inside the media with sub-diffraction resolution through the use of a whole class of non-linear optical (NLO) metal-organic frameworks (MOFs).