Photosensitive Materials and their Applications III

I will explore various facets of photonic quantum systems and their application in photonic quantum technologies. Firstly, I will focus into quantum foundations and by discuss quantum interference, a key element in photonic quantum technologies. I will highlight how the distinguishability and mixedness of quantum states influence the interference of multiple single photons – and demonstrate novel schemes for generating multipartite entangled quantum states. I will then address photonic quantum computing, specifically focusing on the building blocks of photonic quantum computers. This includes the generation of resource states essential for photonic quantum computing. I will then shift to photonic quantum networks, covering both their hardware aspects and showcasing quantum-network applications that extend beyond bi-partite quantum communication. Lastly, I will outline how photonic integration facilitates the scalability of these systems and discuss the associated challenges.

Joining the rich photophysics of organic light-emitting materials with the exquisite sensitivity of optical resonances to geometry and refractive index enables a plethora of devices with unusual and exciting properties. Examples from my team include biointegrated microlasers for real time sensing of cellular activity and long-term cell tracking, as well as the development of photonic implants with extreme form factors and wireless power supply that support thousands of individually addressable organic LEDs and thus allow optogenetic targeting of neurons deep in the brain with unprecedented spatial control. Very recently, by driving the interaction between excited states in organic materials and resonances in thin optical cavities into the strong coupling regime, we unlocked new tuning parameters which may play a crucial role in the next generation of TVs and computer displays to achieve even more saturated colour while retaining angle-independent emission characteristics.

Speckles are a statistical interference phenomenon which arise 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 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 hologram 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. 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.

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, full color recording materials for volume holographic optical elements (vHOEs) and are available at industrial scale. Bayfol® HX is compatible to plastic processing techniques like thermoforming, film insert molding, and casting. 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 well suited to solve these challenges in primary display, and near-infrared imaging applications such as eye-tracking based on a customizable and available tool box, Bayfol® HX can be adopted for a variety of such applications. 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.

Butterfly wings have hierarchical structures that are responsible for their structural colour and can influence their optical anisotropy. The scale patterns influence the interaction of polarised light. In this work, the optical anisotropies (linear and circular birefringence, and dichroism) of a wing sample of a butterfly were experimentally measured and mathematically modelled using Jones calculus. Inspired by the results from the biological samples analysis a number of photonic structures were recorded in azo-dye polymers. The novel photonic structures are evaluated with the help of the developed theoretical model and their sensitivity is assessed theoretically in view of their application as transducers in optical sensing. This research could develop the biomimicking of such structures and utilising them in sensing.

Photo-induced isomerization of azobenzene molecules drives mass migrations in azopolymer samples. Hence, it is of paramount importance to find quantitative observables that could drive the community towards a better understanding of this mass-transfer phenomenon down to the nanoscale. In this work, we use AFM to map the azopolymer local elasticity and viscosity, with high resolution. A model for the nanomechanical structuration of the azopolymer sample is also proposed.

In response to the growing demand for compact space instruments, this study focuses on enhancing the UV resistance of a photopolymerizable glass used in volume holographic optical elements. The current material, developed through a sol-gel technique, demonstrates quick curing, stability under high humidity and temperatures, but susceptibility to UV-induced cracking. The research aim is to improve UV resistance, noting that thicker layers exhibit reduced resistance. The study explores the approach of single-beam post-exposure which is found to decrease the UV exposure detrimental effect on layer properties. Additionally, the impact of chemical composition variations, such as dye concentration and plasticiser addition, on material UV exposure resilience is investigated. Optical properties, including diffraction efficiency and refractive index modulation, are assessed before and after UV exposure to evaluate material performance.

A subwavelength structure made of a resonant waveguide grating embedded in a luminescent sol-gel layer for a double color effect. The resonant waveguide grating is formed of a diffraction grating and a high refractive index guiding layer using a TiO2 based sol-gel. NanoImprint technology is used to get the micro structuring on the silica sol gel layer. The resonant structure is then embedded in a thin layer of silica sol-gel doped with Rhodamine B phosphors allowing visible emission under UV illumination. Preliminary results will be presented from the modelling and design of the microstructure to initial demonstrators.

Metasurfaces, structures which are tailored artificial arrays of metallic or dielectric nanostructures, are a promising approach for controlling light propagation and its characteristics, like amplitude and/or phase distribution in space. Active (or tunable) metasurfaces allow to control light not only in space, but also in time. One strategy to achieve tunability of metasurfaces is to use phase change materials (PCMs), like vanadium dioxide (VO2), as their constituents. By changing a critical parameter, as temperature, the PCM dielectric function suffers drastic variations, which may strongly alter the metasurface’s light extinction properties. Two specially designed metasurfaces employing VO2 will be discussed. One presents Mie resonances in the visible and another quasi-Bound States in the Continuum resonances in the Mid-IR. I will show that these resonances can be continuously modulated in their amplitude by factors up to ~8 dB, representing an important way to control 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 study investigates the piezophototronic effect in zinc oxide (ZnO) thin films produced through physical vapour deposition (PVD). The piezophototronic effect combines piezoelectricity, semiconductor characteristics, and photoexcitation properties in materials. Traditionally, it has been explored in piezoelectric thin films under external mechanical stress for controlling carrier injection, transport, and recombination. This enhances the efficiency of optoelectronic devices, including photovoltaic cells, photo-transistors, LEDs, and photodetectors. However, the interaction of the light exposure with the piezoelectric properties of ZnO thin films has not yet been investigated. This work evaluates the piezoelectric coefficient (d33) of ZnO thin films using direct and indirect methods, and its response to ultraviolet light exposure, proving its validity for enhanced sensing platforms and energy nanogenerators.

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. 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 our materials, simulated a design parameter space to obtain a theoretical maximum Δε of 0.63, and grew a prototype device. By measuring the temperature-dependent FTIR spectroscopy, our prototype device demonstrated FP-cavity enhanced adaptive thermal emittance.

The ability to control solid-gas phase transitions using light as a stimulus has attracted significant interest in the field of materials science because it gives rise to a large volume change. In most cases, this transition is caused by photothermal heating of a volatile liquid. In this work, we use a photochemical mechanism for gas generation that is based on using organic azides undergoing UV photolysis to release gaseous nitrogen. 2-Anthraceneazide is doped into a 150µm thick polymer films that release nitrogen microbubbles on the film surface when irradiated in a water reservoir. The formation of nitrogen bubbles was observed using optical microscopy, and their size and distribution were characterized using image analysis. The effects of various irradiation conditions, such as irradiation time and light intensity, doping concentration of azide, and film surface on the formation of nitrogen bubbles were investigated. The results indicate that the size and distribution of the bubbles can be controlled by adjusting the irradiation conditions and film surface morphology.

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.

We have successfully designed, fabricated, and demonstrated the use of volume holographic lenslet array illuminator (VHLAI) and a volume holographic axial multi-plane illuminator (VHAMI) respectively for high speed confocal imaging applications. Our results demonstrate the potential of using volume holographic multifocal generation approaches for uniform array generation as well as simultaneous multi-plane illumination. The main idea is to use volume holographic gratings in both cases to selectively produce lateral focal point array and axial focal points in multiple planes inside the sample and then use confocal pinholes to simultaneously image these multiple points. The proposed systems can greatly reduce image acquisition time while maintaining image quality. These systems are suitable for in-vivo and high-speed volumetric imaging for both biomedical and industrial applications.

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 ap- plications. 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.

The detection of volatile organic compounds (VOCs) is an area of growing interest due to the detrimental health effects as a result of human contact with VOCs. Holographic structures have been demonstrated as highly robust sensors for several analytes including VOCs. In this work, the sensitivity of a number of different holographic structures is compared with unslanted holographic gratings for several common VOCs. Furthermore, the effect of doping the holographic gratings with nanoparticles as well as coupling of the holograms with a cantilever transducer is investigated. The novel optomechanical transducer is demonstrated to have significantly enhanced sensitivity.

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 diffractive sensors, surface morphology is a key parameter. Two approaches for optical patterning of photopolymers with different chemical compositions will be presented and compared. They allow the fabrication of surface structures on the micron scale directly into a photopolymer layer. The first approach utilizes 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. The second approach involves the use of a digital micromirror array spatial light modulator. This approach allows for the creation of surface relief patterns with features as small as 3 μm2, with significantly higher pattern complexity. Surfaces fabricated with both approaches in photopolymers with different chemical compositions are characterised and compared in view of their application in diffractive optical sensors.

Simple photopolymer based on Cellulose Acetate Butyrate (CAB) as binder which hosts pentaery thritol tetrakis[3-mercaptopropionate (PETMP) is developed to make surface and volume phase patterns transferred by means of a Direct Laser Writing (DLW) approach. 1D and 2D gratings, as well as complex Computer Generated Holograms (CGHs) are printed and fully characterized to highlight the contribution og surface phase shift and volume phase shift. Moreover, the diffraction efficiency is measured and correlated to the writing conditions.

The study introduces innovative holographic diffusers made from acrylamide or diacetone acrylamide-based photopolymers, designed for treating visual conditions like amblyopia and diplopia. Spectral analysis revealed that diffusers with high diffusion efficiencies (>90%) showcased minimal (<5%) reduction in efficiency across the visual spectrum from 420 to 700 nm. Notably, diacetone acrylamide-based holograms exhibited significantly lower toxicity than those made with acrylamide, which is crucial for applications involving children. Additionally, accelerated ageing tests demonstrated sustained efficiency, even after an estimated 6 months. These findings support the potential of these diffusers for medical use, emphasising their minimal spectral impact, reduced toxicity, and enduring performance, all vital for addressing visual impairments.

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 also reported the use of nanostructured polymers that possess highly branched main chains, the so-called hyperbranched polymer (HBP) as another candidate for size and refractive-index controllable organic nanoparticles. In this presentation we show that a photopolymerizable NPC dispersed with the ultrahigh refractive index HBP of 23-25 vol.% provides a volume holographic grating possessing the refractive modulation amplitude as large as 0.03 at grating spacing of 500nm and at a recording intensity of a few mW/cm^2 in all the visible spectral regions of the blue (405nm), the green (532nm) and the red (640nm). Such a high contrast volume holographic grating can be used for volume optical holographic elements in a wearable display for augmented and mixed reality.

By replicating holographically inscribed sinusoidal surface relief structures, we fabricated PDMS-based diffraction gratings that can serve as optical transducers for volatile organic compounds sensors. The proposed sensing method relies on diffraction efficiency modulations induced by the analyte expanding the PDMS and altering its refractive index by filling its pores. By experimentally investigating the thermal dependence of the diffraction efficiency of the proposed structures, we observed a non-negligible in the contexts of this optical transducer (up to 0.42%) and non-linear change in diffraction efficiency with temperatures ranging from 10 to 60 °C. Here, we investigate the intrinsic properties of PDMS that influence the optical signal of the surface relief gratings when temperature of the surrounding is varying.

Optical cavities with nonlinear elements and delayed self-coupling are widely explored candidates for photonic reservoir computing (RC). For time series prediction applications that appear in many real-world problems, energy efficiency, robustness and performance are key indicators. With this contribution I want to clarify the role of internal dynamic coupling and timescales on the performance of a photonic RC system and discuss routes for optimization. By numerically comparing various delay-based RC systems e.g., quantum-dot lasers, spin-VCSEL (vertically emitting semiconductor lasers), and semiconductor amplifiers regarding their performance on different time series prediction tasks, to messages are emphasized: First, a concise understanding of the nonlinear dynamic response (bifurcation structure) of the chosen dynamical system is necessary in order to use its full potential for RC and prevent operation with unsuitable parameters. Second, the input scheme (optical injection, current modulation etc.) crucially changes the outcome as it changes the direction of the perturbation and therewith the nonlinearity. The input can be further utilized to externally add a memory timescale that is needed for the chosen task and thus offers an easy tunability of RC systems.

Programmable photonic circuits manipulate the flow of light on a chip by electrically controlling a set of tunable analog gates connected by optical waveguides. Light is distributed and spatially rerouted to implement various linear functions by interfering signals along different paths. A general-purpose photonic processor can be built by integrating this flexible hardware in a technology stack comprising an electronic monitoring and controlling layer and a software layer for resource control and programming. This processor can leverage the unique properties of photonics in terms of ultra-high bandwidth, high-speed operation, and low power consumption while operating in a complementary and synergistic way with electronic processors. This talk will review the recent advances in the field and it will also delve into the potential application fields for this technology including, communications, 6G systems, interconnections, switching for data centers and computing.

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 bending of holographic grating fringes parameters as third grade polinomial's coefficients. \\

Currently, one of the main challenges for scientific research is the improvement of energy performance in many areas such as in the buildings sector and industry. The large amount of energy used makes it necessary to move to efficient and environmentally sustainable aspects in this field. In this sense, Holography can offer a significant improvement by storing reflection holograms in a photopolymer material with chromatic selectivity. Reflection holograms can be applied for reflecting part of the visible spectrum depending on the angle of incidence of the light. Using a commercial material Bayfol HX200 to store reflection holograms high diffraction efficiency can be reached for the visible wavelength range. In this work, up to two high-efficiency reflection holograms have been multiplexed in the same layer due to the physical thickness of the Bayfol HX200 films. Once multiplexed the pairs of holograms at different recording angles we have stuck several layers together. From this multilayer multiplexed system, we have obtained a wide diffracted spectrum in which the result is the superposition of all the multiplexed gratings recorded in each layer.

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 when applications are required in which the material must retain its structural integrity in liquid media. It is necessary to carry out a first incubation process in solutions that contain the components necessary for the storage of volume phase holograms in these hydrogels. 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 these components on the diffraction efficiency of stored holograms has been investigated.

This research involved the synthesis of gamma-aminobutyric acid-coated silver nanoparticles through a photoreduction process. The nanoparticles exhibited optical properties associated with the Surface Plasmon Resonance effect, possessed a spherical shape, a crystalline structure, a negative surface charge, and showed good stability. Sunflower seeds were treated with these nanoparticles for 24 hours, resulting in nanopores forming in the seed coat. This promoted efficient water absorption and the activation of essential reactive oxygen species, which in turn broke seed dormancy and facilitated germination. Notably, chlorophyll-related assessments revealed a significant increase in chlorophyll production and improved seed growth following nanopriming.

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.

We present a phase mask design method to generate an AAF beam with a cubic chirp-modulated axiconic phase. The proposed method is flexible in tuning the beam parameter to obtain various shapes. It is straightforward, and an input beam can be directly transformed into the AAF beam using a single element. The results are useful for designing and controlling the dynamics of an abrupt autofocusing beam and its variants for various applications.

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 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 10^4 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).

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 holographic 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. The laser ultrasonics involves irradiating an object with a laser pulse to produce an ultrasonic vibration, and then using another laser beam 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 precise measurements that are unaffected 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 numeric analysis that computes the director orientation as a function of the retardance across specific voltages (grey level) is compared to experimental results. More specifically, this work is focused on analyzing 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. In this paper, we show programmable DOEs produced using vertically-aligned LCoS (VA-LCoS) devices, with a phase-shift range largely exceeding 360º. We focus on the production of binary and blazed gratings and on the analysis of their higher diffraction orders, showing interesting possibilities for applications, such as the enlargement of their numerical aperture.

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.

This research delves into the potential of three-dimensional graphene GiiTM foam as a versatile material for optoelectronic devices. The study evaluates the chemical structure of GiiTM foam using Raman spectroscopy at various wavelengths and laser parameters. Two types of GiiTM foam, standard graphene (ST-Gii) and low resistance graphene (LR-Gii), are compared, highlighting differences in their electronic properties. Notably, ST-Gii displays a significant change in its G/D intensity ratio when exposed to different light wavelengths, indicating potential applications of GiiTM foam as optoelectronic switch in optoelectronic devices. The study also includes the design and characterization of a photo-resistive detector based on ST-Gii, providing insights into its photo-response and light current as a function of visible light wavelengths.

How to reduce surface work function, improve quantum efficiency and extend sensitive wavelength has been the hot issue for metal photocathodes. In order to improve the photoemission performance of metal photocathodes, the graphene/metal van der Waals heterojunction photocathodes were prepared through surface modification, like a specific Cs/O activation process. The photoemission behaviors, including light-excited current, spectral response and degradation characteristic were investigated. The photoelectron spectroscopy results present the changes of the chemical states of surface elements and the corresponding work function after Cs/O activation and degradation. This composite photocathode can provide a technical approach for the development of photocathodes.