This PDF file contains the front matter associated with SPIE Proceedings Volume 11030, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

In this paper, the determination of the topological charge of the vortex beams by means of shearing interferometry was achieved, for both common and non-common path shearing interferometers, using simple yet effective optical elements. The recording and analysis of interference patterns from different setups was accomplished using: cyclic, rotational and reversal shearing interferometers. The use of cyclic and rotational shearing interferometers resulted in interference patterns with two oppositely oriented forks for both setups. However, with the reversal shearing interferometer, a single forked pattern was obtained and a mathematical approximation was deduced.

Registration of two types of digital holograms is considered: digital hyperspectral holograms and Denisyuk volume holograms (holograms in colliding beams). Hyperspectral holograms are considered as an analogue of thin holograms, in which zero order and a conjugate image are suppressed. Previously proposed principles are developed for the case of thick holograms in their digital representation. It is shown that the displacement of a scanning mirror in the process of hyperspectral holograms capturing is analogous to registering of the blackening function of layers of the volume hologram. The position of the mirror corresponds to the layers in a thick hologram, where the interference pattern is recorded in layers. An analogy is drawn between the restoration of a hologram by a light beam and its processing of its digital analog.

A compact and cost-effective lens-in-lens common-path interferometer for quantitative phase imaging of objects in white light as well as in narrow spectral bands is proposed. The optical system of the interferometer includes three lenses. The first component of the interferometer consists of two lenses with the same focal length, but different diameters. The lens with the smaller diameter is installed inside the hole in the bigger diameter lens. The light wave is thus divided into two beams. The second component is a single lens. A pinhole is placed between the first and the second components in their joint focal plane. The pinhole serves as a spatial filter to form a reference wavefront from one of the beams passed through the first component. The reference and the object beams are collected by the second component, and the digital holographic pattern resulting from their interference is registered by the camera. The performance of the system is demonstrated by quantitative phase imaging of red blood cells, onion cells and nylon fiber with use of green and red laser light sources.

Nanocomposites photonic materials are being actively studied for practical applications such as touch screen, wearable devices, optical sensors, photolithography, and neutron optics. For many of these applications, it is essential to fabricate embedded phase structures into media, in order to implement various properties for its practicality. High-contrast refractive-index changes with promising flexibility are usually desired for these applications. Photopolymers as an appealing candidate are attractive because they hold several advantages, such as low cost, ease of use, shape flexibility, large-area process ability, and self-development capability. In this work, we carried out single-wall nanotube doped polymer composites, which are based on acrylate-thiol-ene photopolymer material. It is shown that a substantial increase in refractive index modulation and diffraction efficiency is realized by doping both of BzO₂ and single-wall nanotubes. Moreover, the incorporation of BzO₂ lowers the optimum recording intensity to 0.25 mW/cm². These results indicate that carbon nanotube-polymer composite provides effective method to fabricate flexible films with large-area holograms for wearable devices, display, and optical sensor uses.

We report on an experimental investigation of recording a plane-wave volume holographic transmission grating in a photopolymerizable nanoparticle-polymer composite film dispersed with hyperbranched-polymer (HBP) organic nanoparticles in an acrylate monomer blend codoped with an electron donor and acceptor photoinitiator/inhibitor system. The HBP organic nanoparticle possesses the ultrahigh refractive index of 1.82 at 532 nm owing to the inclusion of triazine and aromatic ring units, which provides a large difference in the refractive index between HBP and the formed polymer. It is found that the recorded NPC grating with 23 vol.% HBP dispersion possesses the saturated refractive index modulation amplitude as large as 4.5 x 10^-2 at 532 nm and at recording intensities of a few mW/cm². Obtained results suggest the use of our newly developed HBP-dispersed NPC as volume optical holographic elements for wearable display for augmented and mixed reality.

The fabrication of Polyvinyl Alcohol/Acrylamide (PVA/AA) and the addition of a photo-sensitizer have been fully investigated. The creation of self-written waveguides (SWW) has also received much attention and their results have been very promising. In this paper we look at the optical loss across the SWW and also subject the SWW to coherence testing to analyze the wave form and measure any degradation in the optical signal. With the fabrication of the PVA/AA we use a photo-sensitizer or dye which is Erythrosine B (EB), which is sensitive to wavelength of λ = 532nm. We characterize a multi-mode (MM) fiber across various aspects such as attenuation profile and birefringence. We then cut the optical fiber and prepare it for cleaving. The fiber ends are then cleaved and then set into a V-Groove. The fiber ends are 7mm apart and in direct line or optical trajectory. This is then covered with a soluble form of photo-sensitized PVA/AA. When the PVA/AA is cured an optical light source (OLS) is connected to one end of the fiber. This OLS has a broadband light source capability from 400nm to 1700nm. An optical power meter (OPM) is connected to the other end of the fiber, this OLP also has the capability to receive and analyze wavelengths within the spectrum 400nm to 1700nm. The OPM is turned on the wavelength λ = 532nm propagates along the fiber until it enters the PVA/AA. The self-writing process begins and with the change in refractive index and the introduction of polymer chains a SWW is created. The SWW is now situated between the two fiber ends with an length matching the fiber distance of 7mmThe wavelength then enters the open optical fiber and the propagates along the fiber to the OPM. At this stage the analyses of the 532nm wavelength gets underway and the optical fiber link is re-characterized. At this stage a wavelength is characterized and measure against the original attenuation profile (AP) and birefringence measurements. The wavelength is also examined under spectral analyses using a spectrum analyzer and compared to the original wave form to measure interference and coherence. This will allow us to understand the characteristics of a SWW with fibers interconnecting and exposing the wavelength directly to the PVA/AA within its structure. The tests carried out investigate attenuation profile (AP), birefringence, polarization effects and interference. The SWW is characterized so that future use as a directional splitter/coupler created within a SWW can be used effectively within an integrated devise and within communication networks.

We present a high performance, removable light trap for the suppression of Fresnel reflections from optical substrates used in holography. When recording holograms with coherent illumination in photosensitive materials, Fresnel reflections lead to undesired interference patterns, producing parasitic gratings. These parasitic gratings consume dynamic range of the material, impact hologram uniformity, and produce stray light on playback. A reflection as small as 4% (glass-air) will produce interference patterns with fringe visibility 0.38. Typical methods for suppressing reflections are often prohibitive in holography, either due to spectral and angular requirements, cost, or potential for contamination. Antireflection-coatings have limited spectral and angular performance, in addition to high cost for one-time use. Relying on polarization suppression of reflections at Brewster’s angle is impractical for the wide range of angles required in most holographic recording applications. Index matching oil with neutral density (ND) filters limit recording orientation and oil often contaminates the samples. We show that by incorporating an absorber into different elastomers, the refractive index of common optical substrates may be matched, and recording light absorbed. Adhesion between the soft elastomer and glass provides sufficient hold while still allowing the layer to be easily removed after use, with no residue or surface damage. Reflection suppression occurs over broad angular and spectral range, with reflected intensity limited only by the index difference between substrate and elastomer. Using carbon black as an absorber, and a poly(dimethylsiloxane) (PDMS) elastomer, we demonstrate a 15 dB reduction of back reflections from a glass slide over a 600 nm bandwidth.

The important effects, techniques, and factors are considered that aim to increase the spatial resolution of a scanning direct laser writing of diffractive structures on thin films of transition metals from titanium group (Ti, Zr, and Hf). The writing process is based on metal oxidation under the thermal action of a tightly focused laser beam. Scanning speed of the laser beam and film thickness were varied to get a regime of through oxidation (TO) of the metal film under laser heating. It results in strong increase of the film transmission in exposed area. TO ensures a strong threshold due to feedback connected with decreasing of laser power absorption near center of focused gaussian laser spot. To the best of our knowledge, the direct laser writing of amplitude diffractive structures on Zr and Hf films were performed for the first time. The new regime of direct laser writing on thin Zr films was revealed. It allows forming tracks with width of 100 nm and less at laser spot diameter of 700 nm and laser wavelength of 532 nm. In this work, the spectral dependence of the refractive index and extinction coefficient of hafnium films was first experimentally determined in the wavelength range of 250–1100 nm.

Photochromic materials belonging to the class of diarylethenes are presented as active materials for the manufacturing of rewritable Computer Generated Holograms (CGHs). Thanks to the modulation of both transparency and refractive index, it is possible to produce amplitude and phase holograms. Regarding the photochromic materials, different properties must be optimized in order to obtain efficient holograms and they are here discussed. As for the writing step, it is possible to use a direct laser writing approach or a mask projection system and both strategies are discussed. Examples of photochromic CGHs (phase and amplitude) are reported.

See-through optical components are being intensively studied in applications such as Head-Up-Displays (HUD) and Head-Mounted-Displays (HMD). In particular, volume holographic optical elements (vHOE) have received a lot of attention due to their unique optical (angular and spectral selectivity) and mechanical (lightweight and thin) characteristics which make them perfectly suitable for use in integrated optical components like spectacle lenses and car windshields. Bayfol HX photopolymer films prove themselves as easy to process recording materials for vHOEs. The Bayfol HX instant developing holographic photopolymer film provides full color capability and adjustable diffraction efficiency as well as an unprecedented optical clarity when compared to classical volume holographic recording materials like silver halide emulsions (AgX) or dichromated gelatin (DCG). Besides the recording step, no pre- or postprocessing is necessary and easy mass production of vHOEs in a completely dry roll to roll process is possible. The layout of a typical Bayfol HX film consists of a light-sensitive photopolymer layer coated onto a transparent thermoplastic substrate. This substrate is particularly beneficial, not only for easy handling of the film during holographic recording, but also for further mechanical processing steps which are required to embed the film into a finished optical component. Once holograms have been recorded and the film has been bleached with incoherent light, the Bayfol HX film becomes inert and can be further processed in normal daylight. Moreover, the presence of a thermoplastic substrate makes the film attractive for use in manufacturing processes such as injection molding, thermoforming, casting, etc…, typically used to fabricate parts for the automotive, eyewear and ID-card industry. Being compatible with these industrial processes is an essential feature for the widespread of immersive Augmented Reality displays based on volume holographic optical elements recorded into Bayfol HX films. In this paper we investigated the compatibility of holograms made with Bayfol HX film with some of the integration processes typically used in the plastic and optical components industry and which are necessary for embedding the holographic films into a finished product.

Two-stage holographic photopolymers capable of high refractive index modulation (Δn) on the order of 10^–2 enable the fabrication of a myriad of optical elements. While there are commercial products available that meet these requirements, researchers often want the flexibility to customize both the form factor of the samples as well as the mechanical and chemical properties for their specific applications. We present a novel high refractive index acrylate writing monomer in a low refractive index urethane matrix as a model material for customization for optical applications. We discuss the achievable Δn of this custom monomer, 1,3-bis(phenylthio)-2-propyl acrylate (BPTPA) in the urethane matrix as a function of solubility, along with a comparison to a commercially available high refractive index monomer, 2,4,6- tribromophenyl acrylate. Formulations with BPTPA exhibit a peak-to-mean Δn ≈ 0.029 in transmission holograms without any obvious deficiencies in transparency, color, or scatter. This writing monomer and the synthetic processes present a promising platform for the fabrication of high-performance holographic photopolymers for a wide range of research applications.

In recent years, the development of low-toxicity photopolymers for holographic recording in reflection mode has reached great importance. One of the main advantages of reflection holograms is that they can be reconstructed using white light, which has enabled that many researches have focused on the development of sensors for different types of analytes. Optical data storage and three-dimensional multiplexing of reflection holograms to improve the data storage density have also been investigated through reflection holograms. However, the photopolymers used in these researches have certain undesirable features such as the toxicity of some of their components and non-environmentally compatibility. The common used hydrophilic photopolymers content poly(vinyl alcohol) (PVA) or gelatine binder and monomers related to acrylamide. This compound has a high potential to cause cancer. For this reason, we developed a photopolymer called “Biophotopol” as a recording holographic material for optical applications. “Biophotopol” have a low toxicity, good recycling properties and is environmental-friendly. The basic formulation of “Biophotopol” includes an initiator system which is a free radical generator composed by triethanolamine as co-initiator and plasticizer and sodium salt 5’- 72 riboflavin monophosphate as sensitizer dye, sodium acrylate as polymerizable monomer and PVA as inert binder polymer. Additionally, a cross-linking agent, as N,N’-(1,2-dihydroxyethylene)bisacrylamide (DHEBA) , can also be added. Volume transmission gratins and holographic lens have been fabricated in this photopolymer but not researches have been done to store reflection gratins. Is know that for higher spatial frequencies, the diffraction efficiency decreases considerably as the spatial frequency increases. In this sense, the general aim of this work has been fabricated reflection gratings in the symmetrical experimental setup in “Biophotopol” and to study the dependence of diffraction efficiency on physical thickness, recording intensity and exposure energy. First, films physical thickness was investigated. The maximum diffraction efficiency was obtained for thicknesses around 145 µm. The photopolymer layers uniformity was highly sensitive to drying and environmental conditions during the exposure stage. Therefore, both conditions were investigated and very controlled. An increase in diffraction efficiency was observed when the photopolymer films were cured with a LED lamp to improve the stability of the reflection holograms. The residual dye is eliminated during this process. The maximums diffraction efficiencies around 30 % were obtained for reflection gratings with a spatial frequency of 4738 lines/mm. The index modulation and optical thickness were obtained by fitting procedure through coupled wave theory. Experimental and theoretical results have been interpreted to modify the photopolymer formulation and exposure conditions in order to increase the diffraction efficiencies.

Photopolymerization can be used in self-developing photopolymerizable resin to recording holographic gratings. The photochemical study outlines the possible existence of photocyclic initiating systems where the dye is regenerated. To study the impact of photoinitaiting system on the hologram grating formation, diffraction curves are compared to those of monomer to polymer conversion. This work outlines the importance of the photochemistry on final holographic material properties.

Within the astronomical field, Volume Phase Holographic Gratings (VPHGs) cover nowadays a relevant position as dispersing elements (DE) because each observation could take advantage of specific devices with design and features tailored for achieving the best performances. The manufacturing of highly efficient and reliable VPHGs require holographic materials where it is possible to precisely control the parameters that define the throughput of the device (namely both the refractive index modulation and the film thickness), this is especially true for complex and novel optical designs, where the realization tolerances have to be strictly fulfilled to achieve the theoretical expectations. Moreover, in the design phase, it is crucial to take into account scattering effects and absorption losses to predict with accuracy the final behavior of the optical element. For this application, the most promising materials are the photopolymers because, beside the ability to provide the tuning feature, they bring also advantages such as self-developing, high refractive index modulation and ease of use thanks to their simple thin structure, which is insensitive from the external environment. Thanks to the advantages made available by photopolymeric materials, in this paper we propose innovative solutions for designing stacked spectral-multiplexed VPHGs and transmission dispersing elements (GRISMs) that can cover more than one octave in spectral range by using more than one diffraction order, providing huge advantages for the astronomers in terms of spectral resolution R or time allocation of the instrument for performing the observations. In this context, we also give hints for the process optimization that is crucial for achieving the results reported.

It is well known that in standard diffaction experiments only the amplitudes of structural Fourier components are recovered but phase information is lost. This problem is known as the ’phase problem’ in crystallography. In this contribution, we point out how the phase problem of diffraction can be solved in some particular cases by employing multi-wave interference. In the experimental situation described here, we were able to determine the form of the refractive-index profile of a 1-D nanocomposite holographic grating by using a multi-wave coupling analysis of the measured angular dependence of the diffraction efficiencies for a number of diffraction orders.

In present paper we report a study and demonstration of rare earth doped photo-thermo-refractive glasses for monolithic integration of laser sources/amplifiers and volume Bragg gratings. Namely, we demonstrated laser action of neodymium and ytterbium-erbium doped photo-thermo-refractive glasses. In addition, we studied the influence of the rare earth dopants on the photosensitivity of photo-thermo-refractive glass. It was shown that introduction of rare earth dopants not only increase the viscosity of the glass that leading to the longer heat treatment time, but also decrease the ability of fluorine to form sodium fluorine nanocrystals in the glass host. In accordance with this data we developed and demonstrated a new glass composition which overcomes these drawbacks and can act as both holographic and laser active medium. Thus new rare earth doped photo-thermo-refractive glass can be very attractive and promising medium for monolithic integration of lasers/amplifiers and volume Bragg gratings on the united laser-holographic substrate.

The Air Force Research Laboratory (AFRL) Directed Energy Directorate is completing a supersonic wind tunnel to characterize aero-optics effects in high speed flow fields. Optical characterization is accomplished by transmitting a beam of light transverse to the direction of air flow via access windows, thereby illuminating the flow region, a select volume of which is recorded by a suite of sensors. Quantitative measurements of the flow are made using two wave-front sensors (WFS), a Shack-Hartmann (SH) WFS and a digital holography (DH) WFS. Qualitative measurements are made using a traditional Schlieren imaging system. Parenthetically, in addition to characterization of aero-optics effects, we expect to be able to numerically propagate to different planes in the supersonic flow field to characterize boundary layer effects. This paper reviews our wind tunnel system’s requirements and, in particular, the design of the DH WFS.

The photorefractive effect of smectic liquid crystal blends containing small amounts of a chiral compound was investigated. Photorefractive ferroelectric liquid crystal blends, composed of smectic-C liquid crystals, photoconductive chiral compounds and a sensitizer, are known to exhibit a large photorefractive effect. Smectic liquid crystal blends containing various concentrations of a chiral compound while keeping a constant concentration of photoconductive moiety were prepared. The effect of the concentration of the chiral compound on the photorefractive properties of the liquid crystal blend was investigated.

Holographic wave front printing is an emerging technique for the fabrication of computer-generated image holo- grams and holographic optical elements based on wave front synthesis via adaptive optical elements. Progress is fueled by the availability of high quality spatial light modulators and industrial grade holographic film materials. Striving for increased relevance for applications, a flexible and precise way of fabricating large-area, highly efficient holographic optical elements providing complex wave front transformations is sought after. In this pa- per, we report on a novel holographic printer setup for the recording of volume holographic optical elements (vHOEs) in a step-wise fashion by adjacently recording many sub-holograms. The setup is centered around two phase-only reflective spatial light modulators, which are used to shape the recording wave fronts. The recording wave fronts propagate through the setup on a common path and interfere in the focal plane of a reversely illuminated microscope objective, where the holographic film is located. The setup is additionally equipped with two characterization beam paths based on CMOS cameras allowing for accurate control of printing parameters and in-situ characterization of diffraction properties of the printed holograms. We demonstrate the recording of high-efficiency transmission vHOEs in development grade Bayfol HX TP* photopolymer in our setup. In order to exemplify the setup’s characterization capability, we present results of test series concerning vHOE diffraction efficiency as a function of exposure dose and the influence of photopolymer development dynamics on multiplexed exposure. Finally, we showcase a printed high-contrast holographic diffuser screen for see-through display applications.

A switchable diffraction device capable of driving with segment electrodes has been proposed and its operating characteristics were analyzed. The switchable diffraction device is based on a variable cavity structure using reversible electrodeposition technology and two kinds of diffraction gratings are designed to be selectively switched according to the driving electrode. The fabricated device was able to switch the diffraction patterns without any interference between the electrodes, which means that the interference between the electrodes will not be a problem in further device integration with driving circuits. However, when the electrode isolation is not perfect due to parasitic resistance between the electrodes, a weak interference between the electrodes is observed in the diffraction pattern. Therefore, it is expected that ensuring complete insulation between the electrodes will be a very important in the integration of the device. The proposed device can be used as a light control device, an image switchable hologram, etc. Furthermore, it is expected to be applied to reconfigurable metasurfaces through integration with active matrix circuits in the future.

Diffractive optical elements (DOEs) assimilate optical functionality within thin (≤100 μm), lightweight films. With the recent advent of high dynamic range two-stage photopolymers, gradient-index volume DOEs can now achieve diffraction efficiencies competitive with conventional surface-relief DOEs, while also offering the advantages of contact-free, selfprocessing optical recording into a flat film that can be laminated between protective sheets. Here we design and fabricate Fresnel lenses with what we believe to be the highest reported diffraction efficiencies achieved to date using this gradientindex DOE approach. Our analysis demonstrates that these high diffraction efficiencies are crucially enabled by the high index modulation of the photopolymer, Δn < 0.01. Another factor enabling high diffraction efficiency is the pixel count of the recording exposure. Thus, we use a photolithographic chrome mask with 9000 × 9000 pixels of 2.5 μm diameter, significantly exceeding the pixel count available from spatial light modulators. The mask is imaged onto photopolymer films of 50 μm thickness, and Fresnel patterns of up to 23 mm diameter are recorded in one-shot exposures. The resulting lenses range from f/44 – f/79 with diffraction efficiencies up to 83%. The performance of various lens designs is validated by an analysis showing that, for a given Δn, there is a fundamental trade-off between low f/# and high diffraction efficiency. This high performance represents an important step toward practical applications, ranging through solar energy concentrators, customized vision optics, integrated photonics, heads-up displays, and hybrid lenses.

Computer Generated Holograms (CGHs) are used for wavefront shaping and complex optics testing. Present technology allows for recording binary CGHs. We propose a Digital Micro-mirror Device (DMD) as a reconfigurable mask, to record rewritable binary and grayscale CGHs on a photochromic plate. Opaque at rest, this plate becomes transparent when it is illuminated with visible light. We have successfully recorded the very first amplitude grayscale Fresnel CGH, with a contrast greater than 50, which was reconstructed with a high fidelity in shape, intensity, size and location. We propose a new Fourier CGH coding scheme leading to a quantification exceeding 1000 within a smaller cell size of 2x2 pixels. This code has been implemented for the BATMAN-instrument logo for visiting very different spatial frequencies. The CGH is recorded with our DMD-based set-up, leading to a 1000x1000 pixels hologram written on a photochromic plate. The reconstruction of the recorded images with a 632.8nm He-Ne laser beam and an imaging lens leads to images with a perfect fidelity in shape and intensity, for any single pixel of the original object. Our proposed code exhibits a much higher resolution, a better compacity and an increased throughput, in comparison with the current Fourier CGHs. These results reveal the high potential of this method for generating programmable/rewritable CGHs.

Continuous-wave THz digital holography (DH) is an advanced interference imaging technique, which can be used to reconstruct the amplitude and phase distributions of a sample. In this paper, an in-line holographic system is presented using a 300 GHz source and a highly sensitive broadband CMOS TeraFET (THz Field-Effect Transistor) detector. Numerical reconstruction is achieved using the angular spectrum approach. Experimental results are presented for a sample made of Polyvinyl Chloride (PVC). The results demonstrate that THz digital holography can be readily applied to perform quantitative metrology and may find many applications in 3D digital imaging and microscopy.

THz in-line holography, is a simple and effective way of three-dimensional (3D) imaging. In this work, a THz in-line holography system is presented to investigate the imaging performance. An electrical multiplier-chain emitter working at 300 GHz was utilized as illuminating source. A highly sensitive broad-band CMOS TeraFET detector mounted on a 2D mechanical translation stage for raster-scanning acted as a virtual camera to record the hologram. The data capture area was 60x60 mm² with a pixel size of 0.25 0.25 mm². The test objects were polyvinyl chloride (PVC) boards, one taped with 2-mm-wide straight aluminum stripes separated by 2-mm intervals, another one taped with 1.5-mm-wide aluminum stripes forming the word ’GUF’ (size of each letter: 6x8 mm²), and the other two with the same patterns, but now realized as grooves in the material. The imaging results show that a resolution of at least 2 mm is achieved, with a large dynamic range of 60 dB due to the high sensitivity of the TeraFET detector. A property of in-line holography is its self-homodyning capability with the consequence that, in addition to the intensity, also the phase information is encoded in the hologram. The phase information of the transparent part of the object, and of the scattered and diffracted waves are retrieved with the same spatial resolution as the intensity, revealing the 3D imaging capability of the system. The quality and fidelity of the image results can be substantially improved in the future by enlarging the recording area and using an iterative phase recovery method. Furthermore, with a camera substituting the single-pixel scanning technique, the system will have the capability of real-time imaging. Combined with the 3D imaging ability, it will then have a wide application range for various topical areas.

New application of photo-thermo-refractive glass (PTR) named “holographic prism” is presented. In the holographic prism angles between directions are set by the holograms which create “fan” of signal beams. This kind of prism creates several signal beams which are equal to the reflections from facets of the conventional silica prism. Implementation of PTR glass as a holographic medium for this device brought us several advantages and new features. First it leads to decrease in overall size of the prism that positively affects the identification process of the beam's crosspoint. Thus, it increases sensitivity and accuracy of the measure. Second, greater value of the refractive index change in PTR glass in comparison with calcium fluoride crystal allows us to increase quantity of the recorded reference beams for the measure which leads to sensitivity increase. During this work, it was found that with uneven exposures the refractive index distribution between the gratings is proportional to their irradiation. Also, we demonstrated various geometries of diffraction responses for a new modification of the holographic prism, with two perpendicular "fans".

Some of the latest developments at CSEM Center Muttenz using diffraction gratings applied for a high resolution spectroscopy, light management in solar cells and LED, color filters, optical security, nano-membrane fabrication etc. will be presented. CSEM Center Muttenz has built a full chain for the grating fabrication, beginning with the design and ending with the optical device. The simulations are made to fulfill the appropriate properties of reflected/diffracted light for the planned application. This permits to fully specify the grating geometry: period, profile, duty cycle and depth. Gratings (linear or crossed) are initially fabricated in a photoresist using a Laser Interference Lithography (LIL) with periods going from 220nm up to 2000nm this on a surface of 5”. If needed the gratings can be transferred into the substrate (glass, Quartz, steel or dielectric) using a dry etching processes and a Cr masking. With this technology flat substrates can be structured with gratings, but also concave or convex surface can be processed. Different grating shapes are available like: sinusoidal or quasi-sinusoidal, triangle, rectangular, “U” type or blazed. This technology allows adjusting the duty cycle of the rectangular gratings, 20/80 is the minimum we can achieve but, this will depend on the depth to period ratio requested. A typical value we can achieve as “Depth to Period” ratio is 1.6. Most of the applications involving gratings will need a hard copy, the later can be made into glass, or a SolGel type of material like, Ormocer or also with a Ni shim. The Ni shims are useful for replication like hot embossing, including the Roll to Roll processes, UV casting. It allows transferring the grating structures into different flexible polymers, like PMMA, PC, PET etc. Specific metals or dielectric materials deposited on the gratings will permit to create different requested color effects.

We report the results of a thorough investigation into the initial stages of the photo-thermo-induced crystallization process in photo-thermo-refractive glass. The spectral location of the absorption peak characteristic of the surface plasmon resonance in the silver nanoparticles is known to be highly sensitive to the dielectric parameters of the nanoparticle surrounding. We have studied the evolution of the peak location in the course of PTI crystallization process and shown that the red shift of the peak in glass is caused by the occurrence, around the silver nanoparticles, of highly-refractive shell of a mixed nature. The blue shift of the peak that can be observed under the reduced speed of the process was shown to be inflicted by the precipitation of sodium fluoride crystals. During further analysis was proven that shell is of 5.7 angstrom thickness. A couple of models examining shell possible evolution was proposed, namely sodium bromide and silver bromide crystal solid solution and silver bromide inclusions into the surrounding glass layer. Both approaches were modeled to obtain surface plasmon resonance shifts equal to experimentally observed ones. It was shown also that the observed blue shift of the plasmon resonance peak at the later stage of PTI crystallization is due to the NaF precipitation.

First experimental demonstration of the device, providing measurement of Zernike polynomial in the incoming wavefront by the use of the Fourier-hologram, recorded with the use of diffuse scattered beam. Signal to noise ratio of such approach was investigated. It is shown that one can easily realize such a device, providing simultaneous and noise-lacking measurement of several dozen Zernike modes.

The paper considers optical linear encoder based on diffraction gratings. A method of quadrature signals phase shift stabilization based on the application of head grating with specific structure is proposed. The optical scheme of position encoder based on measuring head grating with specific structure is developed and described in this paper. Mathematical modeling of quadrature signals phase shift depending on grating parameters is carried out. Based on the simulation, we propose optimal parameters of head grating structure. Design process and results for head gratings are presented in the paper.

In the case of in-line digital holographic microscopes the retrieval of the phase information is indispensable to remove the twin image noise and to characterize the thickness and refractive index distribution of the measured objects. The existing phase reconstructing algorithms, especially, when the goal is to reach high resolution, suffer from really slow convergence. This can prevent their practical applicability. We introduce here a simple method that ensures accurate, high resolution and fast phase retrieval from two holograms recorded in different distances. The so far frequently applied phase retrieval algorithms converge with tolerable speed if the Fresnel number of the system is small enough. This is the consequence that in this case the diffraction of the twin image spreads substantially over the applied object support and thus the support constraint can provide sufficient amount of data for the efficient phase retrieval. However, if the recording measurement Fresnel number is small, the finite aperture of the hologram limits the proper recording of the high spatial frequencies of the object diffraction. In this case the convergence of the phase retrieval will be really fast, but inaccurate. Therefore, we propose to record two different holograms with small and large Fresnel numbers accordingly. From the first one we can reconstruct the low spatial frequencies of the object at a high rate. Subsequently, we can use this partial reconstruction to speed up the reconstruction of the so far not correctly recalled high spatial frequencies, by applying the second hologram.

Optical Scanning Holography (OSH) is a technique that records the three-dimensional information of an object through optical heterodyne scanning. This system has two pupils which enhances processing power and spatial filtering capabilities. Analysis of proposed OSH system in this paper includes two configurations of pupil pairs. In the first case, one pupil is a pulse, and the other is a Gaussian function. The OSH system analyses the adoption of a random phase and Gaussian pupil in the latter case. In the proposed system, the optical transfer function of the recording and reconstruction stages is found out. Subjective evaluation of the optical transfer function is investigated in terms of resolution. Simulations are performed for different parameters of the Gaussian function, various random distributions of the random phase pupil and for other objects. These results can be used with sectioning applications.

Escherichia coli (E. coli), a micro size, hazardous bacteria which is responsible for various life-threatening diseases in animals and humans. Generally, E. coli bacteria can be found naturally in the animals and human intestinal tracts which provide necessary synthesis of vitamins. However, E. coli O157:H7 is one of the most dangerous pathogenic strain which produces toxins. E. coli contaminate in number of drinks and food products. Hence early identification and treatment of E. coli O157:H7 is very necessary in order to prevent various diseases. In this work, Digital Holographic Interferometric Microscopy (DHIM) system is used for non-destructive, in-vitro imaging of E. coli bacteria. The major advantage of using the DHIM over the conventional microscopy is that in DHIM both amplitude and phase coming from the specimen can be reconstructed from recorded hologram. It provides three dimensional information of the specimen under test. In DHIM system distortions due to the aberrations are minimized by the interferometric comparison of reconstructed phase with and without the object. The phase reconstruction of recorded object and reference wavefront is calculated by Fourier Transform method. DHIM system is non-invasive, non-contact type and has the potential for fast detection of E. coli.

Micro-flame is a flame having the size of several millimeter (approx. 2-3 mm). Micro flames are used in micro devices such as microsatellite and micro aerial vehicles etc. An understanding of combustion characteristics of micro flame is required for design a burner or combustion system to create micro flame. In this paper, digital holographic interferometry (DHI) is used for the measurement of temperature, temperature profile and temperature fluctuations of a wick stabilized micro diffusion candle flame. By measuring the change in temperature/ temperature fluctuations and radical concentration, we can also measure the quenching in micro flame.

In this work we study and characterize and holographic waveguide system composed of two volume diffraction gratings, which act as optical couplers and a glass substrate that acts as a waveguide. The features such us high diffraction efficiencies and Bragg angle selectivity exhibited by volume diffraction gratings allow the appropriated adjustment of the incident light to be diffracted in the direction of total reflection condition inside the glass substrate with high efficiency. In this work the holographic waveguide is recorded on different photopolymer materials, which optimization is controlled to obtain high spatial frequencies and stable fringes. The effect of the shrinkage of the holograms after recording in the quality of the image obtained from the optical waveguide is also studied. To perform the experiments two kind of photopolymers were studied: a nanoparticle-(thiol-ene) polymer composite, NPC, and a penta/hexa-acrylate based polymer with dispersed nematic liquid crystal molecules, PDLC. The holographic characteristics such as diffraction efficiency or wavelength selectivity obtained with the waveguides recorded on the different photopolymers were also studied and compared.

The interaction of laser light with biological samples acquires increasing importance due to its numerous applications in areas like optogenetics or biophotonics. For many of these applications, it is important to know how light interacts with biological material, if it’s possible to quantify absorption and scattering effects produced and if these effects are local. A useful label-free technique for this purpose is digital holographic microscopy (DHM) that allows to obtain spatial images of living cells being irradiated in real time in a quantitative way, with no contact with cells and with robustness, stability and a rapid data acquisition. The main objective of this work is to perform a quantitative study on laser irradiation of hippocampal cells using digital holographic microscopy. To carry out this study, unlabeled cells samples have been irradiated by low-power continuous lasers of 405 and 785 nm wavelength. The modifications of optical path length (OPL) produced by the interaction have been measured using digital holographic microscope. According to the study conditions, it is shown that the evolution of OPL values is different depending on the irradiated area of the sample, laser power is a factor to consider depending on the wavelength of the laser used, both the OPL values differ and absorption effects occur depending on the laser wavelength used. These findings represent a first step towards the development of a protocol that can be used in the study of light-cell interaction processes using digital holographic microscopy.

The article describes the features of the security elements used in color three-dimensional security holograms. Unlike classical security holograms - "rainbow" relief - phase holograms, color three-dimensional security holograms have spectral and angular selectivity. This feature allows them to create new security elements or use the properties of already known elements as a new. The article describes the schemes and devices for creating such security elements, as well as devices for their visualization and control. Examples of typical security elements used in color three-dimensional security holograms are presented. This work was supported by the Russian Science Foundation (Project No. 18-79-00304).

We report for the first time a regular optical patterns formation in a laser beam propagating through a Fe doped lithium niobate (LN:Fe) crystal. The process was controlled by pyroelectric effect resulting in self-localization of the regular optical pattern in a single light spot with reduced size and displacement relative to the input beam. The experiments were performed with the use of single mode laser radiation at 632.8 nm wavelength and with beam powers of 0.5 ÷ 10 mW. The LN:Fe sample with 0.03 wt% concentration of Fe and 10 mm lengths along beam propagation was used in the experiments. The switching of the pyroelectric effect in the process was achieved by gradual heating of the crystal in the temperature range of 10 ÷ 42 °C during 130 s. The observed phenomenon of optical patterns formation is explained with the light induced complex refractive index variation with a central minimum (negative lens) and symmetric side maxima (positive lenses) due to photovoltaic effect. Light-induced complex lens produces beam defocusing from the beam center and focusing on the periphery. Mutual interference of the beams leads to the regular light patterns formation. The switching of pyroelectric effect results in the space-charge field modification in the crystal, asymmetric positive lens formation and light self-localization.

This paper reports on utilization of a single holographic/diffraction optical element (HOE/HDE) recorded in a photopolymer-based holographic material for monitoring the change of linear dimensions of an object which is in direct contact with the formed HOE. The holographic optical element – transmission grating, is produced by recording of interference pattern generated by two collimated beams from Argon ion laser operated at wavelength 514 nm into a thin photopolymer holographic film. The size of a grating spacing Λ was proposed with respect to range of the investigated deformations in order to be able to observe an effect of external mechanical stress on the grating. The proper experimental conditions for recording of the proposed transmission grating at selected wavelength were determined, first. This was done via recording of several quasi-harmonic phase diffraction gratings at different exposures and comparing their diffraction efficiencies. The chosen grating was then firmly attached to a transparent test specimen made of polycarbonate which was subjected to mechanical stress. The change of the specimen’s dimension was monitored, and at the same time the grating was illuminated by a probing beam from a laser diode module (639 nm) and the displacement of the first diffraction order was recorded. The dependence of the position of the diffraction order, i.e. spatial displacement as function of strain ε provides information on change of grating spacing Λ which is required for analyzing possibilities of utilization of the holographic material for sensor applications.

Protection of documents against tampering and counterfeiting can be accomplished by visually identifiable devices. A key requirement for them is that they should provide unique features enabling verification of authenticity. In stacks of layers with periodic undulations, diffraction and interference effects can be combined together with excitation of guided modes and long-range plasmons to provide large security potential. The studied stacks are composed of a hot-stamped HRI embossing foil, with or without a thin metal film deposited on the foil HRI coating, and they are embossed with diffraction gratings. Designs of stacks are analysed by dedicated numerical methods, with the gratings having sinusoidal profiles of the same modulation depth at each internal interface of the stack. The designs take into account aspects of practical producibility of final foil devices via embossing and vacuum deposition techniques. Corresponding experimentally realized samples are tested by angular and spectroscopic scatterometry.

The linear canonical transforms (LCTs) are a Lie group of transforms including the Fresnel and Fourier transforms that describe scalar wave propagation in quadratic phase systems. As such, they are useful in system analysis and design, and their discretisations are important for opto-numerical systems, e.g. numerical reconstruction algorithms in digital holography. An important topic in the literature is therefore the generalization of Fourier transform properties for the LCTs. A number of authors have proposed convolution theorems for the linear canonical transform, with different goals in mind. In this paper, we compare those methods, with particular attention being paid to the consequences of discretization. In a similar way to how discrete convolution associated with the DFT differs from that associated with the Fourier transform, we must take the chirp-periodic nature of discrete LCTs into account when determining the discrete convolution associated with LCTs. This work is of significance for the simulation of VanderLugt correlators, which have been used for optical implementations of neural networks, and for optical filtering operations and coherent optical signal processing in general.

One of the promising methods for manufacturing high-aperture and sub-wavelength diffractive optical elements (DOE) is direct laser writing on thin metal films in regime of through oxidation. The amplitude diffractive metal/oxide structure is formed directly by localized laser heating without post-processing using liquid or dry etching. Optical diffractometry based on an analysis of the diffraction pattern obtained from a locally illuminated region of the grating is quite suitable indirect method for inspecting the metal/oxide gratings with a submicron period. Measurement of the angular distribution of diffraction orders allows determining local period of the DOE structure, and measuring the intensity distribution over all diffraction orders allows determining the duty cycle of the grating. In this paper, the configurations of instrumentation schemes of metal/oxide gratings monitoring and algorithms for processing of diffraction patterns formed at illuminating the metal/oxide gratings by probe laser beam are considered.

The manufacturing methods and materials for diffractive optical elements are actively developed due to the prospects of their use in various components of the microsystem technology. Photolithography occupies a central place in modern manufacturing technology for such components. The photoresists used in it can be exposed to high (100-150 degrees) temperatures, treated in a liquid environment, aggressive (alkaline, acidic) fluids, reactive ion etching (RIE), and electrolyte exposed to electrochemical deposition of metals. Therefore, the development of photoresist materials with thermo-, plasma-, chemo- and moisture resistance is relevant and of the high interest at this time. One of the promising classes of organic compounds with photoresistive properties is the chalcones. It is shown that polyfluorochalcones are capable of providing the holographic recording of transmission gratings with diffraction efficiency up to 59% and angular selectivity up to 54.5°. The masking and thermal properties of triacrylamide polyfluorochalcon (TAPCh), its triaryl pyrazoline modification (TAP), as well as modifications by prepolymerized triaryl pyrazoline (polyTAP) under liquid chemical conditions (in H₂SO₄, H₃PO₄, NaOH) and reactive ion etching (in plasma CF4) were investigated. A comparison of properties with commercially available photoresists SU-8, AZ4562 was also conducted. It has been shown that TAFH is resistant to liquid etching, which is the same for SU-8, but shows higher results in RIE process; TAFH exceeds the performance of photoresist AZ4562 in resistance to RIE, and significantly exceeds it in liquid (alkaline and acid) etching; thermal stability TAFH exceeds SU-8 and AZ4562.

The development of specialized non-destructive methods for monitoring of microstructured optical elements is necessary for introduction of diffractive, micro-optical and conformal optical elements into production. However, a wide variety of such elements, as well as their production technologies, set many tasks in the implementation of process control both at the final and at the intermediate stages of the formation of a multilevel and binary phase element. All this requires the use of various expensive equipment, each of which individually does not allow solving the whole range of tasks. Multichannel scanning measuring system that implementing spectroscopic and diffraction testing methods was developed at IAE SB RAS. The device includes four measuring channels allowing to measure the following parameters and characteristics: transmission function of half-tone masks in zeroth order or as sum of all diffraction orders; thickness of transparent films covered on substrate (by the spectroscopic method in reflection); measurement of the zero-order intensity of diffraction structures, both in transmission and in reflection in range of wavelengths from 200 nm to 1100 nm; measurement of the diffraction efficiency of the first and zero orders of diffraction in reflected light (including for structures made in optically transparent materials) for monitoring the parameters of the formed relief of multilevel elements.

Silver Halide emulsions have been considered one of the most energetic sensitive materials for holographic applications, due to a high energy sensitivity and wide spectral sensitivity. Based on these characteristics and the appearance of Ultrahigh resolution silver halide emulsions, have been performed Silver Halide Sentitized Gelatin (SHSG) holograms, it is high-sensitivity recording grattings, performed with laser wavelengths anywhere within the visible spectrum and high diffraction efficiencies, getting the final hologram with properties similar to a Dichromated Gelatin (DCG) hologram. This simplifies the manufacturing of high-quality, large-format Holographic Optical Elements (HOE’s). In this communication we studied several development processes of Silver halide emulsions, more concretely we analyze the influence of a combination of different developer agents, from a single one up to 4 developer agents, based on ascorbic acid developer agent. We studied the influence of the developer combinations and its effects on the transmission spectra for a wide exposure range by use of 9 μm thickness films of ultrafine grain emulsion BB640, exposed to single collimated beams using a red He-Ne laser (wavelength 632.8 nm) with Denisyuk configuration obtaining a spatial frequency of 4990 l/mm recorded on the emulsion, with an energetic sensitivity of 100 μJ/cm2. The experimental results show that an optimized solution (pH and development time) of ascorbic acid as the only developer agent could be the best solution to get high efficiency reflection diffraction gratings (up to 90%) and up to 70 nm of bandwidth.

The two-dimensional non-separable linear canonical transform (2D-NS-LCT) can model a wide range of paraxial optical systems. Digital algorithms to calculate the 2D-NS-LCTs are of great interested in both light propagation modeling and digital signal processing. We have previously reported that the transform of a 2D image with rectangular sampling grid generally results in a parallelogram output sampling grid, thus complicating further calculations. One possible solution is to use interpolation techniques. However, it usually leads to poor calculation speed and reduced accuracy. To alleviate this problem, we previously proposed a unitary algorithm by choosing an advantageous sampling rate related to the system parameters. In this paper, a fast algorithm is further proposed based on a novel matrix decomposition, which can significantly improve the efficiency of the numerical approximations.