Holography: Advances and Modern Trends VIII

During the last decade a number of volume holographic media have been investigated that could serve not only as diffractive optical elements (DOEs) for light but also for slow neutrons. In this contribution we discuss the light optical properties of a stack of two gratings separated by an optically inert slice recorded in a Bayfol®HX photopolymer. While the refractive-index modulation of the gratings for light is remarkable, the corresponding neutron optical analogue is, so far, in the medium range of other materials investigated. We therefore aim at possible improvements which are discussed in this manuscript.

Designing a pure phase multifunctional diffractive optical element (M-DOE) is a challenging task, as the regular summation of multiple pure phase functions results in a complex function. One of the widely used multiplexing methods to design a pure phase M-DOE is the random multiplexing method. In this method, different pure phase functions are multiplied to mutually exclusive binary random functions before summation. However, M-DOEs designed using the random multiplexing method are prone to scattering noise. In this study, a novel approach based on a modified Gerchberg-Saxton algorithm (GSA) has been proposed and demonstrated for the design of pure-phase multifunctional DOEs. In this approach, the complex M-DOE obtained by regular summation is used as a reference, and with suitable constraints, the amplitude component of the complex M-DOE is transported into the phase component, resulting in a pure phase MDOE. This modified algorithm is called Transport of Amplitude into Phase based on GSA (TAP-GSA). This method has been demonstrated on a well-established incoherent digital holography technique called Fresnel incoherent correlation holography (FINCH). In FINCH, it is necessary to multiplex two-phase masks, which can be achieved using random multiplexing or polarization multiplexing, resulting in reconstruction noise and low light throughput, respectively. Under low-light conditions, random multiplexing is a better choice than the polarization multiplexing method. The M-DOE designed using TAP-GSA for FINCH improved the light throughput and exhibited a higher SNR in comparison to the random multiplexing method.

Holographic Optical Elements (HOEs) have the potential to enable more compact, versatile and, lightweight optical designs, but many challenges remain. Volume HOE’s have the advantage of high diffraction efficiency but they present both chromatic selectivity and chromatic dispersion that may impact on their use with wide spectrum light sources. Single-colour LED sources have a narrow spectrum that reduces these issues and makes them better suited to use with volume HOEs. However, the LED source size must be taken into consideration for compact volume HOE-LED systems. A theoretical and experimental study was carried out to investigate the design limits due to size of the extended LED source and potential misalignment from the ‘ideal’ position for a range of HOEs.

Wounds that fail to heal impact the quality of life of 2.5 % of the total population. The costs of chronic wound care will reach $15–22 billion by 2024. These alarming statistics reveal the financial strain for both the medical industry and society. A solution can be found in compact and accessible sensors that offer real-time analysis of the wound site, facilitating continuous monitoring and immediate treatment, if required. Benefits of these sensors include reduction of cost and, can extend the reach of healthcare to remote areas. The progression of a wound site can be closely monitored with holographic optical elements (HOEs) by real-time quantification of wound healing biomarkers, such as oxygen, temperature, pH and lactate. Fabrication of such wound monitoring sensors requires biocompatible, water-resistant photosensitive materials suitable for specific functionalisation with respect to wound analytes. Here, the design and fabrication of a HOE for delivering an excitation light beam to the sample chamber of a photoluminescence-based wound monitoring system is reported. We present a photopolymerisable hybrid sol gel (PHSG) material, capable of recording a 60 % diffraction efficiency holographic waveguide. A 1692 ± 5 lines/mm slanted transmission HOE has been theoretically designed and fabricated in PHSG films to in-couple a 633 nm beam into the oxygen sensing site. An identical grating has been used to out-couple the 633 nm beam out of the system. Stability of the PHSG grating post 476.5 nm recording was achieved by two techniques, 532 nm uniform illumination and UV-curing. The unform exposure to laser light was proved to be the more successful method since UV exposure was demonstrated to result in layer damage due to accumulated stress. The potential of waveguides as light filtering optical elements is also explored.

We propose, theoretically explore, and experimentally demonstrate “optical drill” beams presenting nonstationary intensity distributions that resemble the spinning mechanical drill. Optical drills appear as the spatiotemporal interference of two Bessel-vortex beams of different topological charges and different carrier frequencies. By mixing a pair of high-order Bessel beams, synthesized using a liquid crystal spatial light modulator, optical drills of tuned helicities were experimentally observed, and the simplest cases of matter processing with such beams were demonstrated. Optical drill beams could open new and revolutionary perspectives in dynamical material processing by light or in cell and particle manipulation in biomedical applications.

State-of-the-art multi-Petawatt laser facilities coming online include the Zettawatt Equivalent Ultrashort pulse laser System (ZEUS), a user facility being commissioned at the University of Michigan. The 3-PW pulses will make ZEUS the highest power laser in the USA. This talk will describe the various experimental approaches that can be used to produce ultrashort particle beams and light-sources, as well as their application to study strong-field plasma physics and beyond. One area of interest is to create extremely strong magnetic fields within the hot plasma in the laboratory, so we can study the microphysics likely to be occurring around the most energetic objects in the universe.

Laser Plasma Accelerators (LPA) rely on our ability to control finely the electrons motion with intense laser pulses. Such manipulation allows to produce giant electric fields with values in the TV/m exceeding by more than 3 orders of magnitude those used in current accelerator technology. Controlling the collective electrons motion permit to shape the longitudinal and radial components of these fields that can be optimized for delivering high quality electrons beam or energetic photons. To illustrate the beauty of laser plasma accelerators I will explain the fundamental concepts we recently discovered, and I’ll show the maturity of our approach in delivering particle and radiation beams for societal applications including for radiotherapy with the ebeam4therapy EIC project.

On December 5th, 2022, the National Ignition Facility in Livermore, California, USA performed the first experiment demonstrating controlled fusion ignition in the laboratory. With a 2.05MJ UV laser drive energy delivered to the target, a neutron yield of 3.15MJ was released by the fusion reactions in the capsule, providing a net target gain of ~1.5×. The results of this experiment will be discussed, along with the decades-long developments in optical materials, laser architectures, target fabrication, and target diagnostics enabling this recent accomplishment. We will discuss the next steps for NIF and provide an outlook on future applications and technologies, including the reinvigorated pursuit of Inertial Fusion Energy.

Video microscopy has a long history of providing insights and breakthroughs for a broad range of disciplines, from physics to biology. Image analysis to extract quantitative information from video microscopy data has traditionally relied on algorithmic approaches, which are often difficult to implement, time consuming, and computationally expensive. Recently, alternative data-driven approaches using deep learning have greatly improved quantitative digital microscopy, potentially offering automatized, accurate, and fast image analysis. However, the combination of deep learning and video microscopy remains underutilized primarily due to the steep learning curve involved in developing custom deep-learning solutions. To overcome this issue, we have introduced a software, currently at version DeepTrack 2.1, to design, train and validate deep-learning solutions for digital microscopy. We use it to exemplify how deep learning can be employed for a broad range of applications, from particle localization, tracking and characterization to cell counting and classification. Thanks to its user-friendly graphical interface, DeepTrack 2.1 can be easily customized for user-specific applications, and, thanks to its open-source object-oriented programming, it can be easily expanded to add features and functionalities, potentially introducing deep-learning-enhanced video microscopy to a far wider audience.

A photorefractive liquid crystal was incorporated into laser ultrasonic measurement equipment. Laser ultrasonics can be used to investigate the shape and inner structure of materials without contact; its development is expected in manufacturing, construction, and medical industries. Ultrasonic waves are generated by irradiating an object with laser pulses and observing how the waves travel through the object using another laser. The objective is to precisely detect ultrasonic vibrations generated on the object’s surface. Using the photorefractive effect, ultrasonic vibrations can be precisely detected with a sensitivity of less than one wavelength. However, known photorefractive materials exhibit a slow response and require a high voltage to activate the photorefractive effect. Photoconductive smectic liquid crystals respond much faster than conventional photorefractive materials. Liquid crystals that exhibit a flexoelectric effect produce substantial photorefractive effects with a fast response. In this study, we constructed a high-precision laser ultrasonic non-contact measurement system using smectic liquid crystals that exhibit the photorefractive effect. With its fast response time, the system is not affected by vibrations in the measurement environment and can be applied to portable high-precision measurement devices.

We present a novel waveguide-based approach that enables custom wavefront shaping and holography by employing a non-linear electro-optic spatial light modulator. The device consists of a metamaterial electrode cladding that modulates the Barium Titanate waveguide on a sub-wavelength scale. Our generic modulation principle employs electric fields and non-linear optics to create any desired wavefront and is applicable to Pockels and Kerr cells as well as liquid crystals. Here, we present the operation of our tunable waveguide based SLM, specifically for its use as high-quality holographic display.

Fresnel incoherent correlation holography (FINCH) is a well-established incoherent digital holography technique for imaging objects with an enhanced transverse resolution. In FINCH, the beam splitting and self-interference is achieved either using spatial random multiplexing or polarization multiplexing methods. FINCH with inline configuration requires at least three camera recordings of phase-shifted holograms. The above multiplexing methods and multiple camera recordings reduce the power efficiency and temporal resolution respectively. In this study, we propose and demonstrate single shot FINCH with a high-power efficiency using two recently developed computational methods Lucy-Richardson-Rosen algorithm and transport of amplitude into phase based Gerchberg-saxton algorithm respectively.

LEDs have long been hailed as a sustainable light source. Indeed, its adoption in recent decades has greatly improved the efficiency of artificial light sources. Nonetheless, the sustainability claims are challenged by mounting evidence pointing to the detrimental impact of light pollution due to blue-rich white LEDs on wildlife, human health, and astronomy. A potential solution to this is the use of holographically recorded diffractive optical elements (DOEs) to redirect LED light to regions where illumination is required. However, current limitations on the use of DOEs are high costs, low angular working range (Δθ), and relatively narrow spectral working range (Δλ). This restricts their efficient use to narrow wavelength range light sources at highly specific ranges of incident angles. In order for DOEs to be operational with broad Δθ and Δλ, a low thickness and suitably high refractive index modulation (Δn) are required, but it must still operate in the Kogelnik regime and not lose energy to higher diffraction orders. The aim of this review is to identify candidate materials for the design of a novel low-cost DOEs with higher Δn.

Solar concentrator systems represent an important challenge in our society for outstanding photovoltaic (PV) applications. Conventional refractive lenses such as Fresnel lenses, or parabolic mirrors concentrate sunlight in a small solar cell surface. On the one hand, Fresnel lenses have an exceedingly small acceptance angle and require expensive tracking systems to follow the path of the Sun. On the other hand, conventional parabolic mirrors need periodic maintenance of the surface reflectivity. Holographic optical elements (HOEs) represent a suitable alternative to Fresnel lenses and solar reflectors, they are cheaper and more versatile. Particularly, multiplexed holographic solar concentrators (HSCs) give an insight into promising possibilities for Building-Integrated Concentrating PV (BICPV). A good trade-off between wide acceptance angle and high diffraction efficiency (HSCs) represents an important milestone in the area. Our research group obtained the higher acceptance angle in a multiplexed HSC design (Morales et. al. Opt. Express 30, 25366 (2022)). This design was composed of seven holographic multiplexed lenses in Biophotopol material with thick thickness, 197 µm. In the present work, more efficient HSCs than previous works are shown. As far as we know, it has been obtained the best trade-off between high efficiency and wide acceptance angle HSC-PV solar cell systems.

As the risk of antibiotic resistant pathogens increases, development of convenient point of care devices is essential. Such devices would help avoid infection – ensure cleanliness of environments and assist in bacteria analysis. The ultimate aim of the research presented here is to develop a compact, cost effective, easy to use optical device which is capable of detecting and quantifying bacteria in an aqueous sample. The surface relief patterns have a dual role, they provide a diffracted light signal, and control the adhesion of the bacteria to the surface. The strength of the diffracted signal is expected to provide a quantitative measure of the number of bacterial cells attached to the patterned surface. An adjustable holographic set up for controlled patterning of a photopolymer surface using three-beams of varying intensity, incident angles, and state of polarisation was built. The system allows for the creation of surface relief cross-gratings (SRCG) of unit cell size ranging from 8 x 8 um2 (125 lines / mm) to as small as 1 x 1 um2 (1000 lines/ mm). The surfaces are analysed via AFM, Phase contrast Microscopy, Fast Fourier transform analysis of the collected images and diffraction efficiency measurements. The surface relief amplitude dependence on recording parameters is investigated, the results demonstrate a strong dependence of the surface relief height on the period of the recorded structures. The largest surface relief amplitude achieved is 300 nm at 8 um period. The possibility to achieve control over surface roughness by optical patterning was experimentally confirmed. The production and characterisation of large area uniform SRCG, with controllable patterns will allow further experiments aiming at the development of bacterial assays to be completed, namely SRCG contact copying in water resistant materials and their functionalisation by coating.

A simple theoretical model has been developed to calculate the incident beams angles needed to record volume holographic optical elements (VHOEs) for operation as holographic waveguides with any defined input and output angles avoiding the use of prisms. VHOEs are designed to couple 633 nm beam into the layer for three different incidence angles of the input beam To verify the theoretical model the couplers are fabricated using Bayfol HX 200 TM photopolymer at 532 nm and probed at a range of wavelengths.

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. Therefore, Bayfol® HX is ideally suited in applications such as Head-up-Displays (HUD), Head-mounted-Displays (HMD), free-space combiners, plastic optical waveguides, and transparent screens. 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, while maintaining the requirements on optical performance. We demonstrate practical examples of Bayfol® HX vHOE’s using novel holography techniques for spatially varying diffraction efficiency.

In the last few years, the interest in storing volume holograms in photopolymers has increased enormously due to their applications in industry, the medical field, security, or renewal energy among others. The production of environmentally compatible photopolymers is one of the main focuses of Holography research. In this work, we have studied how to increase the diffraction efficiency of reflection holograms stored in a low-toxicity PVA-based photopolymer called Biophotopol. The holographic material has been doped with different types of nanoparticles (NPs) to achieve an increase in the refractive index modulation during the recording stage. Metallic NPs, obtained by physical and electrochemical methods have been used. The results obtained with all of them have been compared as a function of the concentration used, the size of the NPs, and the stabilization method used for their synthesis. A considerable increase in diffraction efficiency has been achieved by using NPs in the low-toxicity material. By using high refractive index NPs, the average refractive index of the holographic material increases and consequently the diffraction efficiency.

Volume Phase Holographic Gratings (VPHGs) are dispersing elements widely used in astronomical spectrographs and they are considered the baseline for the future instruments thanks to the very high efficiency and easy customization. The use of photopolymers and in particular of Bayfol(R)HX materials by COVESTRO AG allowed for the development of a simple production process without chemical wet processes and for innovative instrumental configurations. At the moment, more then 10 BayfolHX based VPHGs are mounted on telescopes all over the world and available for the astronomical scientific community. In this talk, the results obtained and the perspective will be reported.

This work has focused on the optimization of the washing stages of the hydrogels based on acrylamide and N,N’-methylenebis(acrylamide) once unslanted transmission holograms have been stored. For the purpose of determining the compositions of the wash solutions, High-Performance Liquid Chromatography and UV-visible measurements have been employed. PBST and DMSO:H2O 6:4 are used as solvents in the washing stages. The diffraction efficiencies are measured during the washing stages and after the storing of the holograms during several days in PBST. Maximum diffraction efficiencies of 38 and 27.6% are reached when PBST and DMSO:H2O are employed, respectively, for the washing process.

In the fabrication of planar diffraction gratings, the geometric shape of amplitude modulation profile and the refractive index, as well as the spatial frequency, are the parameters that determine the value of the diffraction efficiency and the number of diffracted orders that are generated, when the periodic structures are illuminated. The spatial shape of the Bragg plane profiles is related to the nonlinear responses of the periodic structure, and therefore is responsible for obtaining a high number of diffraction orders. In a holographic grating fabricated with a single exposure, all Bragg planes are identical and have the same geometric profile. In this work we make the diffraction grating plane by plane, modifying the geometry and amplitude of each one of the Bragg planes. To obtain the grating, we record the intensity distribution generated by a Gaussian beam, in an ultrafine-grained emulsion. The optical system is composed of a 405 nm laser and a 50x LWD objective, as well as an automatic mechanical displacement system that allows us to move the irradiation plane every 5 microns, as well as displacement speeds of 15 mm/s. in this way, we can store in the photosensitive medium the Bragg planes, formed by straight lines of different width and depth. The length of each line is 20 millimeters, and its width has varied between 1.4 and 2.5 microns, depending on the focusing intensity and displacement speed, as well as the developer used. By varying the focal plane of the Gaussian beam, it is possible to generate profiles with different geometries. With this technique, diffraction gratings of 20 lines per millimeter have been obtained, allowing a high number of diffracted orders to be generated. BB450 holographic emulsion developed with AAC has been used as photosensitive medium. The images obtained by digital holographic microscopy are presented, reaching profiles of the exposed area

A focused electron beam was used to interact with the chalcogenide thin film substrate. The result of the interaction is presented as controlled relief formation on the substrate surface after etching in an alkaline amine solution. By managing focused electron beam parameters, diffractive optical elements and hidden image effect by means of digital hologram have been recorded. As a result, reflected laser beam of the thin film substrate in the near field represents the hidden image that has been recorded along the hologram in the background. The possibilities of practical usage of this substrate as the material for the production of holograms and diffractive optical elements are discussed.

Detecting volatile organic compounds (VOCs) is important, their presence in modern indoor environments being associated to health risks including respiratory diseases and cancers. State-of-the-art VOCs sensors as MEMS and semiconductor devices achieve high sensitivity but exhibit poor selectivity and high cross-sensitivity with other environmental analytes including temperature and humidity. Such sensors often require complex and costly fabrication/operation processes and/or expensive readout equipment. Here, a novel optomechanical sensing platform, based on the combination of a holographic diffractive element and a static deflection bilayer cantilever, is presented. Its operation principle is based on the differential response of the cantilever layers to target analytes, and was verified using COMSOL Multiphysics. The cantilever deflection due to analyte presence was visually measured. As the sensitive layer is a photopolymer, a transmission volume holographic diffraction grating was recorded enabling a second, more sensitive, detection mode based on the variations in the diffracted beam intensity as the cantilever deflection angle changes. We compared the sensitivity of the optomechanical holographic sensor configuration to that of a holographic diffraction grating in a photopolymer layer coated on a glass slide. Selectivity and sensitivity of both configurations was increased by doping the photopolymer matrix with zeolite nanoparticles. The initial tests monitored the diffraction efficiency changes during the 5 minutes exposure time to 1000 ppm ethanol. The TOS presented changes of 1–4% in diffraction efficiency depending on the dopant concentration and photopolymer layer thickness, while the optomechanical sensor exhibited 7–14% change in diffraction efficiency.

Photopolymers are designed and engineered with versatile applications including optics and photonics. Holography is one of the classical porpoises that use photopolymers as holographic recording materials. The success of these materials can be seen in the market with the photopolymer fabricated by Covestro. Some of these holographic applications require a long-time life of the holograms recorded in photopolymers. Nevertheless, initial tests of Covestro holograms show significant degradation after less than one year of exposure even after sealing and degradation occurs under solar light exposition. In this sense, it is important to perform deeper studies of the different possibilities for hologram conservation. Usually, the first step after recording is the material cure, with UV or visible light, to eliminate the residual dye and monomer. With this process high efficiency holograms can also be obtained. Afterwards, an index matching technique can be used to cover the material with a glass or it is possible the application of aerosol sealant. In this paper we analyze the introduction of holograms between two glasses linked by pressure, using Bayfol HX 200 from Covestro as the recording material. In order to characterize the process, four different spatial frequencies were tested, which were stored either by transmission or reflection schemes. The data of the reconstruction step has been measured before and after the encapsulation. In addition, multiple holograms have been superposed in the same glass, where we have found that shrinkage is more significant

Photonic quantum technologies are a promising platform for a large variety of applications ranging from secure long-distance communications to the simulation of complex phenomena. Among the material platforms under study, semiconductors offer a wide range of functionalities opening several opportunities for the development of integrated quantum photonic circuits. AlGaAs is particularly attractive to monolithically integrate active and passive components since it combines high second order nonlinearity, electro-optic effect and direct bandgap. In this talk, I will present the work of our team on the generation of quantum states of light in the telecom range with nonlinear AlGaAs chips working at room temperature. The talk will review recent developments on monolithic and hybrid integrated devices, describe the versatility of these systems for the generation and manipulation of quantum frequency states and show their potential for the implementation of flexible entanglement-distribution networks for secure communications.

Photonic crystal fibres (PCFs)—thin strands of glass with an intricate array of hollow channels running along their length—offer both hollow and solid glass cores, and allow unprecedented control over dispersion and birefringence, ushering in a new era of linear and nonlinear fibre optics, for example: chiral PCF is circularly and topologically birefringent, supporting optical vortices and in some cases strong circular dichroism; through pressure-adjustable dispersion, gas-filled hollow-core PCF provides an elegant means of compressing pulses to single-cycle durations, as well as underpinning a range of unique sources of tunable deep and vacuum ultraviolet light; microparticles optically trapped inside hollow core PCF van be used to sense physical quantities with high spatial resolution; and strong optomechanical effects in solid-core PCF permit stable timing-modulated high harmonic mode-locking at few-GHz repetition rates.

Volumetric displays make volumetric three-dimensional (3D) graphics composed of voxels that are visualized by light emission or scattering. Since the voxels are directly generated as image points of the object in the real space, the 3D graphics that satisfy the depth perception of the human can be created. One of the promising schemes of volumetric displays will be a laser drawing that used voxels formed by optical addressing with laser beam. The laser drawing method can render volumetric graphics having wide viewing angle because these is no physical wiring between drawing space and system to generate voxels. The most important development is to increase the number of voxels per a unit time. At present, the limitation of the speed of the 3D beam scanning system and repetition frequency of the laser source. In order to improve the drawing speed, the volumetric display systems with a holographic laser-drawing method based on a computer-generated hologram (CGH) displayed on a liquid-crystal on silicon spatial light modulator (LCOS-SLM). In this presentation, we will present recent developments of the volumetric displays using holographic laser drawing.

Manufacturing large-area diffractive lenses is a challenging task as either the outermost width of the zone is beyond the lithography limit or subwavelength. In this study, a holographic approach based on Fresnel incoherent correlation holography (FINCH) has been developed to image objects beyond the resolution limit imposed by the numerical aperture of the diffractive lens. A modified FINCH configuration is proposed where the light modulated by the diffractive lens is interfered with the unmodulated light beyond the diffractive lens and the self-interference pattern is recorded. A computational reconstruction method is used to reconstruct the object information with a super-resolution.

Quantitative phase imaging is the representative of state-of-the-art marker-free full-field optical metrology techniques. We are proposing the phase demodulation algorithmic solution called Deep Variational Hilbert Quantitative Phase Imaging (Deep-VHQPI), where convolutional neural networks were used for automation and acceleration of the previously complicated and arduous fringe pattern filtration and orientation estimation processes. For the sake of metrological figure of merit deep learning-based solutions were employed to accelerate mathematically rigorous Variational Hilbert Quantitative Phase Imaging approach, not to bypass it completely. Deep-VHQPI enables analysis of variety of biological samples and is an important step to simplify optical measurement of biological samples.

Manufacturing large area diffractive lenses (DLs) is a challenging task as, in many cases, the outermost zone width surpasses the photolithography limit and even the scalar diffraction limit. In this study, a non-invasive indirect imaging method is proposed which allows realizing a single large area DL with multiple sub-aperture DLs. The sub-aperture DLs collect light and focus them within the area of the image sensor instead of a single point. This relaxes the photolithography and scalar diffraction constraints. A computational reconstruction method was applied to reconstruct the image of the object from the synthesized point spread function.

Holographic gratings that have been created through the exposing of a specific light beam upon a photosensitive polymer material have been known to also produce self-written waveguides (SWW). We will investigate the SWW and its ability to propagate an optical beam along its path. The reproduction of images processed as information within an optical beam and propagated along the SWW will be tested. The image will be analysed for coherence and clarity. The effect of Birefringence upon the information or image and its optical characteristics will be interrogated measured. The probably of information distortion and the presence will be studied and analysed through research, experimentation and numerical modelling.

Holography represents the recording of a two-dimensional (2D) complex pattern of a wavefront which contains all the information of a three-dimensional (3D) object or scene. This complex-field, consisting of amplitude and phase information, is used to numerically or optically reconstruct the object from the recorded hologram. When a hologram is generated by the numerical methods even in the absence of any physical object, it is called as computer generated hologram (CGH). These numerically generated holograms are optically reconstructed using wavefront modulation devices called spatial light modulators (SLMs). The quantization of both the phase and amplitude improves the reconstruction quality significantly. However, the quantization of either phase or amplitude is done in practical applications owing to the availability of phase-only or amplitude-only SLMs. The matrix dimension may also affect the extent of quantization. This work is an effort to estimate the optimal quantization of CGH for different matrix dimensions.

Efficient live cell imaging requires low doses of lights and ideally non labelled cells, to make sure that markers do not interfere with the cell structure and habits. Quantitative phase imaging is a great tool for these experiments, as it uses very low light doses and does not require externally introduced labels. Especially interesting are common-path straightforward configurations, as they can even work with light sources with low temporal coherence. Our previously introduced grating-deployed common-path QPI system is a great example of such systems, especially since the only modification that it requires, compared to classical brightfield microscope, is the addition of the diffraction grating. The camera records the total shear interference of the conjugate object beams as a self-referenced hologram after grating is used to divide the beams. As a result, it is possible to modify the temporal coherence and suppress coherent artifacts and related noise.. In this work we show the quantitative characterization of the grating-based common-path QPI system and the impact it has on the obtained results. We compare the illumination that utilizes SLED and laser light sources. We use phase resolution targets to evaluate the spatial resolution and phase sensitivity.

Holography is known to be one of the most effective ways to produce visually convincing high quality 3D images. For the automotive applications we target (3D effects for interior and exterior lighting), the cost, brightness and volume of the illumination system impose strong constraints that are generally incompatible with hologram illumination coherence requirements. We propose a method to design holograms that generate a convincing image of a single 3D object when illuminated simultaneously by multiple separate LED sources. This multi-LED illumination allows significant reductions in optical system volume and increases in image brightness. Experimental results obtained with continuous phase holograms fabricated using our in-house fabrications facilities will also be shown along with a functioning reduced volume automotive compatible demonstrator system.

The transmission matrix (TM) measurement is a powerful and well-known tool for characterizing scattering media such as multimode fibers (MMF). Access to the phase of the optical field based on the results of intensity measurements is a long-standing problem known as the phase retrieval problem. To obtain the complex optical field and therefore phase information, it is necessary to use interferences with a known wavefront. In this work, we compare two interferometric methods: on-axis holography with a speckle reference beam propagating through the same optical path and off-axis holography with a plane wave reference beam propagating via an additional arm. These methods, combined with a DMD, provide a fast and accurate way to measure the TM. We present results and a detailed comparison of the two methods of TM measurements of the same system.

In this paper, we propose simple but effective tools to quantify the quality of the optical vortex generated by the SLM. This work was motivated to assist non-experienced users with objective criteria that determine if the optical vortex is of good quality. This, indeed, depends on the particular application, however in general, the user is interested in obtaining as symmetric vortex as possible. Therefore we propose 4 independent quantities calculated over a single-shot intensity distribution of an optical vortex. These quantities examine various vortex features such as contrast, eccentricity, dark-hollow to bright-ring ratio, and singular point position, each time returning the value that can compare various vortices generated within the single setup. The performance of these criteria is shown in the real experimental examples, proving that they can be efficiently applied in modern optical laboratories. With this work, we would like to provide a valuable tool, that can be operated by the non-experienced user in order to correct the imperfection of the optical vortex using digital holography or other setup alignment procedures. All of the presented quantities are available as an open-source, ready-to-use, MATLAB algorithm.

Lensless digital holographic microscopy (LDHM) as a rapidly developing technique of microscale objects investigation requires precise metrological verification examining the accuracy of the novel solutions. LDHM method finds numerous applications in biological specimen and technical objects studies that show diverse optical and geometrical characteristics. Hereby, we introduce custom-designed resolution targets providing an extended quantitative experimental examination of LDHM imaging capabilities in its uniquely wide field-of-view. Proposed structures, manufactured via two-photon polymerization, incorporate the axial thickness and refractive index variation to the qualitative and quantitative imaging analysis.

Gibbs ringing is an artefact that occurs when a discontinuous signal is reconstructed from its Fourier coefficients. The apertures in a digital holographic system can be modelled as truncation in the Fourier domain, meaning they limit the image resolution. The process of apodization introduces Gibbs ringing to holograms of objects with discontinuities. Compressive digital holography attempts to improve image resolution using compressive sensing techniques. Hence, our hypothesis is that Gibbs ringing is reduced by compressive sensing. In this work, we simulate a compressive digital holographic system and investigate how it is affected by Gibbs ringing. We vary the size of the aperture and examine the effects of ringing. This work may aid the further development of compressive digital holography.

For printing static three-dimensional (3D) images, various research groups have developed a holographic recording method commonly referred to as a "wavefront printer." In this work, performance of three optical configurations used in the construction of holographic wavefront printers is compared. We obtain the viewing angles of setups, the diffraction efficiency of recorded holograms, and the structural similarity index measure of reconstructed images in order to assess the performance of a certain set-up. Optical design simulations for each configuration are also carried out to compare the distortions in propagated diffracted wavefront at the time of recording.

Quantitative phase microscopy (QPM) is making waves in live cell imaging owing to label-free time-lapse investigation capabilities. Common-path straightforward configurations are advantageous because of their robustness and stability. Diffraction grating based quantitative phase microscope is a good example of such systems. Grating is employed to decouple conjugate object beams, and their total shear interference is recorded by the camera as a self-referenced hologram (object replica interferes with the object-free background replica; optical path difference between +1 and -1 orders is 0). This allows for the possibility of altering the temporal coherence and suppressing coherent noise (speckle) and artifacts. Generally, in QPM, laser light is used to generate a hologram with encoded sample phase information, and live cells can be impaired by elongated interactions with radiation. To limit the possible photo-damage and photo-stimulation and examine live unimpaired cells in their natural photo-stress-free environment, a low dose of radiation is deployed. In such a low photon budget regime, the signal-to-noise ratio of the recorded hologram can be drastically reduced, which leads to a strong shot-noise presence in demodulated phase maps and deteriorated the quantitative characterization and diagnosis capabilities. In this contribution, we investigate how a low photon budget affects the quantitative examination of phase objects in grating-based common-path QPM. We explore numerical methods to reduce phase noise via additional holograms and phase map filtering.

Nowadays, the study and optimization of volume holographic lenses (HLs) stored in low-toxicity photopolymers have a great interest. HLs are now a component of optical imaging systems that are mostly used in head-mounted displays for virtual and augmented reality or as non-image systems in light deflectors and concentrators. One of the most important parameters used when working with imaging systems is the resolution of the optical system. In this work, the similarity between the object and image of negative asymmetrical HLs stored in a low-toxicity photopolymer named Biophotopol has been evaluated theoretically and experimentally. For this purpose, the resolution of the HLs was calculated using the Convolution Theorem. A USAF 1951 test was used as an object and the impulse responses of the HLs were obtained with two different sensors: CCD and Hartmann-Shack (HS) wavefront sensor. In addition, the resolution of the HLs has been obtained by two different methods: one using the Convolution Theorem, using both the CCD and the HS wavefront sensor, and the other by forming the USAF test image on the CCD sensor. Finally, a theoretical study of object-image similarity was carried out using the MSE (mean squared error) metric to evaluate the quantitative experimental results.

Angiosperms represent nearly 80 percent of all plant species. The outermost layer of the pollen grains of angiosperms is covered in a sticky substance known as pollenkitt, allowing it to adhere to plant and insect surfaces, thus favouring pollination. The primary constituent of pollenkitt are unsaturated fatty acids with varying percentages. However, their optical properties and hence detection are relatively unexplored. Local environmental conditions affect the optical properties of pollenkitt. We propose a label-free method based on in-line digital holographic microscopy (DHM) to quantify the refractive index of pollenkitt of common angiosperms such as morning glory flowers. The adhesive properties of pollenkitt are known to be affected by relative humidity and temperature, causing the refractive index to change. In-line DHM can then be employed to track the refractive index change over time as a proxy for adhesion. This method can also be expanded to quantify the refractive index of pollenkitt of other species.

This paper presents an innovative apparatus for fast and non-contact photoacoustic signal measurements. The apparatus is based on electronic speckle pattern interferometry (ESPI) to record holographic speckles from an object over time. The apparatus consisted of a Mach-Zehnder interferometer, a 532 nm probe laser, and a double exposure camera. Experiments were performed on a tissue-mimicking phantom with a 10 mm diameter spherical optical absorber located 20 mm beneath the surface. Exposure of the phantom to pulsed 1064 nm light resulted in a measurable transient surface deformation consistent with the location and size of the absorber.