This PDF file contains the front matter associated with SPIE Proceedings Volume 12574, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

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 which impact on their use with wide spectrum light sources. Single-colour LED sources have a narrow spectrum that reduces these issues and this makes them better suited for use with volume HOEs. However, the LED source size must be taken into consideration for compact volume HOE-LED systems. To investigate the design limits for compact HOE-LED systems, a theoretical and experimental study was carried out on the effects of an extended source on the HOE output for different holographic lenses, with focal lengths from 2.5-10 cm. The lenses were recorded in Bayfol HX200 material and their diffraction efficiency was characterised across the lens aperture by measuring the Bragg angular selectivity curve at each location. Offset point sources were used to experimentally study the effects of a non-point source on the HOEs and the system was also modelled using Matlab and Zemax.

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.

Structured light is one of the frontiers of modern photonics. It refers to the generation of customized optical fields based on wave-front shaping methods. It is a topic of intense research activity due to the wide range of applications in imaging, nonlinear optics, biophotonics ¹. 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 light matter interaction (fluorescence) with such beams were demonstrated. The rotation in time was achieved by changing the offset of the hologram on the spatial light modulator. Optical drill beams could open new and revolutionary perspectives in dynamical material processing by light or in cell and particle manipulation in biomedical applications.

The photorefractive effect of smectic liquid crystal mixtures was investigated and the application to laser ultrasonic measurements was demonstrated. Smectic liquid crystal mixtures, composed of smectic-C liquid crystals, photoconductive chiral compounds, and a sensitizer, exhibit a fast photorefractive effect. The principle of ultrasonic measurement is that a nanosecond laser pulse is shot on an object to cause an ultrasonic vibration, a continuous laser beam is irradiated on the object, and the ultrasonic variation is detected using photorefractive two-beam coupling. This method can investigate an object's thickness and internal structure without contact.

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, light from an object point is split into two and modulated using two different quadratic phase masks and interfered to obtain the self-interference hologram. The two beams can be generated either by spatial random multiplexing or polarization multiplexing, with the former being power efficient and the latter exhibits a high signal to noise ratio. At least three such holograms are recorded with phase shifts 0, 2π/3 and 4π/3 radians and combined to obtain a complex hologram. This complex hologram can be numerically propagated to reconstruct any plane of the object. Under special beam matching condition, FINCH can exhibit a transverse resolution that is 1.5 times better than incoherent lens-based direct imaging systems with the same numerical aperture. To summarize, FINCH records 3D information with a high resolution at the expense of reduced temporal resolution. Several techniques have been developed in the past to improve the temporal resolution of FINCH by sacrificing transverse resolution and field of view. In this study, a recently developed phase mask design algorithm called Transport of Amplitude into Phase based Gerchberg-Saxton Algorithm (TAP-GSA) and reconstruction algorithm called Lucy-Richardson-Rosen algorithm (LR²A) has been implemented in FINCH. The modified approach with the TAP-GSA and LR²A significantly improved the performance of FINCH with an improved temporal resolution, light throughput and signal to noise ratio.

Solar concentrator systems represent an important challenge in our society for outstanding photovoltaic (PV) applications. 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 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 holographic solar concentrators 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 μm² (125 lines / mm) to as small as 1 x 1 μm² (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 μm 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 theoretical model has previously been developed to calculate the holographic recording beam angles required in air (at any recording wavelength) to produce a Volume Holographic Optical Element (VHOE) for operation as a coupler for different input and output angles. In this paper, the experimental study is extended to further validate the VHOE coupler design and fabrication approach for additional incident beam angles, comparing -40° -45° and -50° (in air). The output angle for each VHOE is +45° within the medium and the coupler operational wavelength is 633nm. Holographic recording in Bayfol HX 200 photopolymer at 532nm is used to fabricate the VHOE couplers. The experimental Bragg curves for each VHOE coupler obtained at 633 nm demonstrate agreement of the measured angles to within ±1.5° (in air) with the expected values.

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. 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 optical dispersing element widely used in astronomical spectrographs. In the last years, the availability of high performance photopolymers allowed for the development of innovative approaches to produce these dispersing elements. The key activities that have been carried out are: i) a production process based on photopolymeric holographic materials (in particular Bayfol®HX by COVESTRO AG) was defined; ii) high quality VPHGs > 170 mm in diameter were manufactured; iii) innovative configurations to increase the dispersion/spectral range were implemented. The effectiveness of these activities is confirmed by the fact that more than 10 devices are mounted on observing facilities and several more are in development or planned. In this paper, we present the VPH technology based on photopolymers.

The storage of time-stable holographic gratings in photohydrogels when the material is immersed in liquid media represents a great challenge at present. A very important stage in the process of storing holograms in photohydrogels are the washing stages to eliminate the remains of the components that have not reacted in the photochemical reaction. The main goal of this work is focusing on the study of the optimization of the washing stages of the photohydrogels 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 in our system. PBST and DMSO:H₂O 6:4 (v/v) 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 38.0 and 27.6% are reached when PBST and DMSO:H₂O 6:4 are employed, respectively.

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

Volumetric displays with a laser excitation of screen materials make voxels in the real space. The laser drawing method can render volumetric graphics with a wide viewing angle because these is no physical wiring between drawing space and system to generate voxels. In our research, a holographic laser-drawing method based on a computer-generated hologram (CGH) displayed on a liquid-crystal on silicon spatial light modulator (LCOS-SLM) is used to increase the number of voxels per a unit time. In this presentation, we will present recent developments of the volumetric displays with the holographic laser drawing.

Manufacturing diffractive lenses with a high numerical aperture (NA) is often a challenging task. The challenge stems from the fundamental limit of lithography techniques and the diffraction limit. Photolithography and femtosecond ablation are some of the well-established rapid lithography techniques for manufacturing large-area diffractive lenses for the visible region. First, when high NA diffractive lenses are designed, the outermost width of the zone becomes a sub-lithography limit (~ 2 μm) while still being super-wavelength. In advanced photolithography and most femtosecond ablation methods, the lithography limit is sub-wavelength, but scalar diffraction is not applicable, and the device becomes polarization sensitive. In this study, a holographic solution to overcome the above limitations is proposed. Fresnel incoherent correlation holography (FINCH) is a super-resolution incoherent imaging technique. In this project, a FINCH-inspired optical configuration is proposed to image beyond the lithography and diffraction limit of the diffractive lens. In a regular imaging system, the light from an object is collected by a diffractive lens and imaged, and recorded by an image sensor in the image plane. In this work, the intensity distribution is not recorded at the image plane but at a plane where the light modulated by the diffractive lens interferes with the unmodulated light outside the diffractive lens. This intensity distribution has spatial frequencies beyond the limit of the NA of the diffractive lens, resulting in super-resolution. Using the newly developed Lucy-Richardson-Rosen algorithm (LR²A), the image is reconstructed. We believe that the developed technique will improve the performance of imaging systems based on high-NA diffractive lenses.

Quantitative phase imaging is the representative of state-of-the-art marker-free full-field optical metrology techniques based on principles of interferometry, holography, microscopy and numerical processing. The measurand is encoded in the phase distribution (optical path delay) of the recorded fringe pattern. To retrieve the measured information the phase demodulation process needs to be performed. Considering the analysis of biomedical samples, the development of very accurate single-frame interferogram/hologram demodulation method is especially important because of the changing nature of the studied phenomenon. In that case the whole process of information recovery can be divided into two steps: (1) interferogram/hologram preprocessing and (2) phase demodulation. We are proposing the “black-box” algorithmic solution called Deep Variational Hilbert Quantitative Phase Imaging (Deep-VHQPI), where convolutional neural networks were used for automation, facilitation and acceleration of the previously complicated and arduous multi-step fringe pattern filtration and orientation estimation processes. It is worth to mention that convolutional neural networks in this work were used for the support of mathematically rigorous quantitative phase imaging algorithm (Hilbert transformation), not with aim to supersede it. For the sake of metrological figure of merit deep learning based solutions were employed to accelerate powerful and well-established VHQPI approach, not to bypass it completely. Deep-VHQPI algorithm enables analysis of variety of biological samples and constitutes an important step towards simplifying optical measurement of complicated and fragile biological samples. Phase decoding results are compared with reference algorithms, i.e., classical VHQPI, the Hilbert-Huang and Fourier transforms. Versatility of the proposed method and its potentially ubiquitous applications in full-field optical metrology are highlighted.

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 wavelength limit. In this study, a computational imaging method is proposed which allows realizing a single large area strong DL with multiple sub-aperture weak DLs. The sub-aperture DLs collect light and focus it into multiple points within the area of the image sensor instead of a single point which increases the width of the zones of the DL. A computational reconstruction method was applied to reconstruct a high-resolution image from the multiple low-resolution images.

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.

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.

Car manufacturers are strongly interested in optical systems producing the perception of an aerial 3D image. Such an effect can be obtained using surface relief computer-generated holograms (CGH). However, classical single light source illumination methods of holograms by a plane wave or spherical wave generally requires long optical path systems that are too bulky to easily fit in a car. In this article, we propose a method to design CGHs that are compatible with multi- LED illumination system while generating convincing 3D aerial images. We also demonstrate an experimental realization of a prototype of a holographic system through the fabrication of a hologram illuminated simultaneously by 6 separate LEDs.

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.

Holography enables 3D visualization of scattered optical fields recorded from three dimensional (3D) objects. This has led to dedicated research efforts towards developments of holographic displays utilizing holographic imaging techniques. The fundamental drawback of holography is that real objects must be used to capture holograms, despite the fact that it is a generic approach for reconstructing 3D information. One of the most promising technologies for addressing this issue is holographic printing which is also able to synthesize combined real 3D and virtual objects. These printers are capable of producing holograms that can replicate all physiological depth signals of actual objects. Reconstructed images are therefore exceedingly realistic and avoid the accommodation-convergence dilemma that other 3-D display methods, such as stereoscopic displays have. Inside a light-sensitive material, reference and signal beams are utilized to create interference, but the recording is local and the procedure is a point-to-point recording of the overall interference pattern. Researchers have contributed in development of different optical schemes for holographic wavefront printers. In this study, we examine the different optical schemes that are adopted for development of holographic wavefront printer and compare their performance. The impact of different optical configurations on the quality of reconstructed images is analyzed in optical design simulation platform and experimental researches. In order to evaluate the performance of a particular set-up, we determine the structure similarity index measure (SSIM), viewing angle of reconstructed image, and diffraction efficiency of the recorded hologram. Experimental and simulated findings are studied and presented.

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 photostimulation 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.

The outermost layer of the pollen of angiosperms, which represent more than 80 percent of all plant species,¹ is covered in a sticky substance known as pollenkitt. The adhesive properties of pollenkitt allows pollen to adhere to plant and insect surfaces, promoting pollination.² These adhesive properties are known to be affected by relative humidity^{3, 4} and temperature, causing the refractive index (RI) to change. We propose a label-free method based on in-line digital holographic microscopy (DHM) to quantify the RI of pollenkitt of common angiosperms, using the morning glory flower (Ipomoea caricia) as an example. We track the RI with (1) local temperature and (2) pollen ageing. This method can also be expanded to quantify the refractive index of pollenkitt of other species.

We have developed an apparatus for fast and non-contact assessment of photoacoustic signals from tissue-simulating media. The apparatus was based on electronic speckle pattern interferometry (ESPI), which in our case featured a Mach- Zehnder interferometer, a 532-nm probe laser, and a double exposure CMOS camera to record the holographic speckles that originated from the surface of a tissue-mimicking phantom. The double exposure camera enabled high speed recording of the speckle patterns at MHz timescales. The speckle patterns were reconstructed into phase and out-of-plane displacement maps of the phantom surface. Experiments were performed with an agarose phantom that contained a 1 cm diameter embedded spherical absorber 2 cm below the detection surface. Exposure of the phantom to a pulsed laser at 1064 nm resulted in photoacoustic waves from the absorber that were detectable at the surface of the phantom. Repeated laser exposure with increasing delay times between the two camera exposures enabled spatial-temporal sampling of the displacement maps. The results show the apparatus could identify the position and size of the photoacoustic source relative to the detection surface. Future work will investigate reconstruction of photoacoustic images from the recorded displacement maps.

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.