This PDF file contains the front matter associated with SPIE Proceedings Volume 11367, including the title page, copyright information, table of contents, and author and conference committee lists.

A photofunctionalisable hydrogel based on copolymers of a nitroveratryl chloroformate derivative with acrylamide has been developed that permits the uncaging of amine groups on exposure to patterns of light at 405 nm using a watersoluble thioxanthone sensitizer. Hydrogel films of 3, 35 and 100 μm thickness were fabricated to use as leaky waveguide and grating sensors. The smallest feature sizes produced in 35 and 100 μm thick films were 21.6 and 43.2 μm respectively, limited by the depth of field of the digital projector. It was found that essentially complete deprotection could be obtained in ~2 minutes. The two thicker hydrogel films were used to create amplitude and phase gratings, while the thinnest film was used as a leaky waveguide to investigate the porosity of the films and monitor immobilization of protein using a PEG linker. The amplitude grating formed by reacting the uncaged amines with fluorescein isothiocyanate was shown to act as a pH sensor with resolution 0.0325 pH units. Protein immobilization using glutaraldehyde as a linker to create a phase grating was attempted, which gave a strong signal with glutaraldehyde but no subsequent signal with BSA. Investigation with a thin film acting as a leaky waveguide showed that glutaraldehyde significantly reduces the porosity of the film to high molecular mass species. Finally, leaky waveguiding was used to monitor protein immobilization using an amine-reactive PEG linker, showing that selective immobilization occurred in the exposed regions of the film without affecting the sensitivity of the film to bulk index changes.

Optical diffusers have uses in laser applications and machine vision. Typical fabrication at a commercial level requires master production and the stamping/copying of individual elements at scale. This expensive, indirect process inhibits custom diffusers at reasonable cost. Previously the authors published a novel, direct, single beam method of recording customizable and controllable volume holographic diffusers by manipulating laser speckle and recording the pattern in photopolymer. This method allows for beam-shaping to produce diffusion patterns of various sizes and shapes. In this work, the direct method of recording controllable holographic diffusers is refined to improve diffuser performance (i.e., a decrease in zero order strength) for a simple diffuser. This is achieved through optimising the recording conditions (exposure energy, power and layer thickness) for a given photopolymer formulation. Significant improvement in the diffuser efficiency is observed through the optimisation process for a particular speckle size, resulting in a five-fold decrease in the remaining zero order. Kogelnik Coupled Wave Theory (KCWT) is explored as a first step towards developing an appropriate model for the behaviour of holographic elements recorded with interference patterns formed through stochastic processes, such as speckle patterns.

To observe three dimensional (3D) in vivo imaging of thick samples in real time, a compact and robust optical sectioning microscope system is required. Recently, we employed static light sheet microscopy (LSM) in which light sheet was generated by a cylindrical lens and objective lens to obtain optically sectioned 3D images. Due to the illumination arm and detection arm are orthogonal to each other in LSM, the photo-bleaching effect of imaging can be reduced and increases the scanning rate so that long-term observation can be achieved. However, the multiple optics in the illumination arm of LSM is too bulky. To overcome this problem, in this work, we show a volume holographic technique can be used to reduce the bulky size of the illumination arm of LSM. Here, we report on design, development, and implementation of holographic light sheet microscope (HLSM) system for in vivo imaging of the biological sample. A VHG corresponding to the wavefront of a cylindrical lens and an objective lens is recorded by superposing it with a reference plane wave into phenanthrenquinone poly (methyl-methacrylate) (PQ-PMMA) photopolymer. Implementation of VHG in LSM makes its smaller and more portable. In order to show the performance of our HLSM, we utilized live Caenorhabditis elegans (C. elegans). Its transparent body allows direct observation of subcellular dynamics with fluorescence-tags. We observed Germline-specific green fluorescent protein (GFP)-labeled embryos and oocytes inside the live C. elegans. As a comparison to bright field microscopy, our HLSM system has inherent optical sectioning ability which helps us in acquiring fine image of the live biologic samples with high contrast. Our method has multiple advantages, including low cost, compact size, easy to implement, and wavelength tunable which makes it suitable for direct implementation in the regular commercial microscope for designing new light sheet microscopic geometries.

The biggest challenge on the path towards high-dimensional imaging is obtaining spatial and spectral information of a volumetric sample in real-time. Advances in this field are of vital importance for biology, material sciences, and medical applications. For example, cancer is one of the leading causes of death in the world, thus gaining a mechanistic understanding of cancer cell processes will significantly impact therapies targeting cancer metastasis pathways. Revealing the entire process with its surrounding environment will require real-time imaging systems that will open the way for better understanding of cancer onset and tissue morphology. This talk will introduce real-time volume holographic imaging systems, which are based on multiplexed volume holographic (MVH) gratings acting as spatial-spectral filters used in conventional optical imaging systems. This allows the acquisition of spatial images with spectral selectivity but without scanning in both transverse and longitudinal directions. In addition, light sheet fluorescent microscopy (LSFM) has recently been utilized to recover 3D images of biological samples. Through pupil engineering, a compact LSFM imaging system will be presented to provide fine optical sectioning capability in more compact fashion. Experimental results of in vivo images of biological samples (e.g. C. elegans) will be demonstrated via our LSFM.

The development and optimization of photopolymers in which time-stable holographic grating can be stored when the material is immersed in an aqueous medium represent a challenge at present. In this sense, the aim of this work was the fabrication of unslanted transmission gratings in a hydrogel matrix which incorporates in its molecular structure a monomer (2-Methacryloyloxyethyl phosphorylcholine) that can act as an anti-fouling agent. The dependence of the diffraction efficiency on the thickness of the hydrogel matrix and the stability of the transmission gratings immersed in water were also studied. An increment in the diffraction efficiency up to 47 % was observed after a washing stage. After two days immersed in water, the holograms showed high stability even though the diffraction efficiency decreased to 37%. The optical parameters were obtained by fitting procedure through Kogelnik’s coupled wave theory.

Holographic recording materials can be utilised in the fabrication of microstructures for use as sensors [1,2]. In order to achieve this the holographic recording material/structure has to be functionalized by incorporation of a chemical component providing sensitivity to a specific analyte/stimuli. We introduce the different approaches to photosensitive material/photonic structure functionalization and present experimental results of fabrication of two examples of sensing devices: for selective detection of sodium and potassium ions and temperature indicator with controlled reversibility. The first example reported here compares the performance of a surface relief grating (SRG) fabricated by holographic lithography in an acrylamide photopolymer and a volume holographic grating (VHG) recorded in a water resistant novel cellulose based photopolymer. The surface relief gratings were modified by incorporation of either dibenzo-18-crown-6 (DC) or tetraethyl 4-tert-butylcalix[4]arene (TBC) as chelating agents [3]. DC coated layers show a selective response to K+ over Na+, whereas for TBC there is a dominant response for Na+ over K+. The sensors respond to Potassium and Sodium metal ions within the physiological ranges. Normal levels of Na+ in human serum lie in the range 135-148 mmol/L and the normal K+ level is 3.5-5.0 mmol/L. The response of the SRG sensor to Sodium is compared to the response of a VHG recorded in a cellulose based novel material functionalized by incorporation of TBC. The advantages and challenges of each of these two approaches to material/structure functionalization are analysed. The second example is a volume phase hologram, recorded in a low-toxicity thermally sensitive photopolymer Poly(N-isopropylacrylamide). Both transmission and reflection holograms were studied by exposing them to temperature ranging within 8-60 oC. It was observed that the reversibility of the hologram response to temperatures above the polymer Lower Critical Solution Temperature (32 oC) can be controlled, thus these devices can be used as elevated temperature indicators. References [1] A. K. Yetisen, et al, Chem. Rev. 114, 10654–10696 (2014). [2] D. Cody, et al, Appl. Opt, 57, No. 22, pp. E173-E183 (2018). [3] Sabad-E Gul, et al, Sensors, 19 No 5, p 1026 (2019).

Recently, a new class of holographic recording materials based on photopolymerisable glass has been developed using the sol-gel technology. Photopolymerisable sol-gel materials have demonstrated excellent capability for volume holography due to their good optical quality and high dynamic range. Other advantages include high thermal and chemical stability, good dimensional stability and robustness because of their rigid matrix. However, the preparation period of non-tacky, dry layers suitable for holographic recording depends on both the sol-gel composition and the sample thickness, and varies from 5 to 21 days. Such a long gelation time is a bottleneck for mass production and this problem needs to be addressed to move the photopolymerisable glass to the next development stage allowing creation of real-world products. This work presents a new photopolymerisable sol-gel glass capable of producing fully dried films using considerably reduced processing time (45 min at 100 °C).The new holographic sol-gel fulfils the required standards of high dynamic range (up to 0.003), high spatial resolution (currently achieved 5600 lines/mm), low scattering, good mechanical and dimensional stability that are necessary for volume holography. Moreover, for the first time the diffraction efficiency of transmission gratings and the spectral response of reflection gratings recorded in holographic sol-gel material under exposure to water have been characterised and their stability have been observed. This provides further perspectives for utilisation of the novel photopolymerisable glass for applications where stability of the photonic structure and its non-sensitivity to ambient conditions change are crucial.

In present work we perform analysis of the recorded Bragg gratings on the PTR glass. The analysis includes rigorous couple wave theory and Kogelnik’s theory. Rigorous coupled wave analysis of the recorded gratings includes up to 11 waves. This analysis allows us to retrieve the phase and the amplitude of the Fourier coefficients of a 1-D grating. Which in turns allow to reconstruct the profile of the grating inside the glass volume. Reconstructed profiles of the refractive index inside the gratings explained by the photo-thermo-induced crystallization mechanism.

Materials research in holography has attracted significant interest and is aiming at facilitating the development of light-weight, cost effective optical devices. Among the most researched materials, photopolymers are playing an indispensable role due to many advantages they offer such as their self-processing nature, high spectral sensitivity and relatively inexpensive mass production cost; hence they are extensively studied to make possible the applications of holographic technology such as holographic interferometry [1], holographic solar concentrators [2], holographic data storage [3] and holographic sensors [4]. Additionally photopolymers can be easily functionalised utilising different methods; one approach, previously proven to be successful, is to dope the host polymer with nanoparticles (NP’s) [4].

We demonstrate for the first time the use of nanodiamond in constructing holographic nanoparticle-polymer composite transmission gratings with large saturated refractive index modulation amplitudes at both optical and slow-neutron wavelengths, resulting in efficient control of light and slow-neutron beams. This is so because nanodiamond possesses a high refractive index at optical wavelengths and large coherent and small incoherent scattering cross sections with low absorption at slow-neutron wavelengths. In the first part of the work we describe the synthesis of nanodiamond, the preparation of photopolymerizable nanodiamond-polymer composite films, the construction of transmission gratings in nanodiamond-polymer composite films and light optical diffraction experiments. Experiments of slow-neutron diffraction from such gratings will be described in the second part.

In the second part of our presentations we discuss the results of diffraction experiments from nanodiamond-polymer composite gratings performed with slow neutrons, i.e., at wavelengths longer than a nanometer. One goal of our investigations is to develop flexible, handy, low cost neutron diffractive optical elements (gratings) which can be tailored to serve as mirrors, two-port beamsplitters, multiport beamsplitters, polarizing beamsplitters or even can be assembled to form an interferometer. Basically three adjustable multiplicative parameters are decisive for the performance, i.e., the reflectivity or diffraction efficiency, of such gratings: the wavelength of the neutrons, the thickness and the neutron scattering density modulation of the grating. While the _rst is solely determined by the application one has in mind, the second parameter can be adjusted during the production process of the sample or by tilting the grating about an axis parallel to the grating vector, thus increasing the effective thickness. The third parameter, however, can only be tuned via the production process of the gratings but offers an enormous flexibility due to a variety of nanoparticles and the polymeric host materials at hand. For neutrons the important criteria are to design gratings having high coherent scattering length density modulation while avoiding incoherent scattering and absorption at the same time. For interferometric purposes an ideal grating will have high reflectivity and low angular selectivity. Here, we show first results obtained with nanodiamond-polymer composite gratings and outline potential ways to improvements.

Augmented reality is still in its infancy and is projected to grow substantially over the next few years. Grating-based waveguides are now established as the key enabling display technology for merging the physical and digital worlds in implementations as diverse as near eye displays, auto HUDs and large-scale retail displays. Despite significant design effort, delivering wide field-of-view (FoV) color, daylight-compatible brightness and ultra-compact glasses-like form factors at an acceptable price remain major development hurdles for consumer AR displays. The form factor challenge is only partially met using thin waveguides; current picture generation units, comprising the microdisplay beam splitter and projection optics, are increasingly seen as too bulky to satisfy the aesthetic requirements of consumer eyewear, while traditional input, fold and output grating architectures occupy too much waveguide real estate. Brightness and power consumption are compromised by losses of typically 95% incurred in coupling light from a picoprojector into a waveguide. DigiLens is prototyping a compact wide angle, full-color laser-illuminated consumer AR waveguide based on its Integrated Dual Axis (IDA) waveguide architecture which uses Digilens’s proprietary Switchable Bragg Grating (SBG) technology. An IDA waveguide multiplexes beam expansion and extraction gratings using a high index modulation holographic LC-photopolymer material system optimized for wide angle multiplex grating applications. A 50-degree diagonal FoV, full-color, low-cost IDA waveguide lens was demonstrated at the Consumer Electronics Show (CES) in Las Vegas (January 2020). As shown in Figure 1, DigiLens’s current waveguide display range includes helmet (25° diagonal), smart glass (30° diagonal) and head-worn (50° diagonal) color waveguide displays.

This work aims to optimise the sol-gel material for use in a holographic concentrator. After chemical optimisation, characterisation of the material’s performance in different regimes of thickness, spatial frequency and recording wavelength are carried out in order to design optimal devices for different solar concentrating roles. An innovative approach to the recording process is introduced in order to account for the range of spatial frequencies involved in a light concentrating optical element such as a holographic lens. A spatial light modulator is utilised to spatially vary the intensity of the recording beams in order to account for the frequency dependent optimum recording intensity. Holographic lenses recorded in this fashion in both photopolymer and sol-gel is compared. Solar cell efficiency with and without the holographic lenses is compared. The lenses are prepared with a specific device role for use with or without solar tracking systems. The efficiency of these systems and the degradation to the device due to solar UV radiation is considered, both are compared for systems based on photopolymer and sol-gel systems.

Diffractive Optical Elements (DOEs) utilize diffraction at sub-micron features to re-direct and control light. Volume phase holographic materials, such as photopolymer, are advantageous for use in fabricating optical elements because the diffraction efficiency can approach 100%, the whole element can be recorded in one exposure and high diffraction and slant angles are possible. Self-developing photopolymers also facilitate mass manufacture. Holographic gratings have been developed for numerous applications including spectroscopy, solar concentration, and monochrome LEDs, however, the inherent angular and wavelength selectivity of the volume phase hologram generally restricts applications to laser systems and sources with narrow spectral ranges. Multiplexing more than one grating into a single photopolymer layer can extend the range, however, unwanted additional gratings are frequently recorded. In this paper, we discuss laminating multiple photopolymer HOEs together as a method for increasing the wavelength and angular working range of devices. This involves combining HOEs designed to produce the desired output beam for different angular and/or spectral input beams. Stacking of photopolymer layers has previously been demonstrated to increase the angular range of gratings and recently the authors produced a compound HOE with significantly broadened wavelength and angular selectivity curves by laminating two HOEs recorded sequentially at a single wavelength. However, such solutions are not easily translated to more complex elements such as lenses where the spatial frequency and grating slant angles are varying. This paper discusses laminating together two photopolymer layers sensitized for different recording wavelengths for the purpose of holographically recording a compound-element volume-HOE lens for use with a broadband LED. The angular and wavelength selectivity are characterized and the challenges and advantages of the different approaches are discussed and compared.

This presentation is devoted to methods of multiplex volume Bragg diffraction gratings production. One of last developed and most promising volume photosensitive material of a such gratings is a photo-thermo-refractive glass. Low photosensitivity and high cost of suitable lasers for this material is a huge disadvantage. This makes traditional interference method of Brag gratins production difficult to implement. Thus a new method or a new vision of previous methods of a Bragg grating production required. A scheme of optical replication of easy-to-earn relief-phase grating into volume medium is considered. A mathematical modelling of interference field forming in volume medium during this process and attained diffraction efficiency of Bragg grating is performed. Experimental research at pulsed and CW lasers setups were carried out and achieved samples of multiplex Bragg grating described. A method of vibration-independent and low-sensitivity-material-suitable optical replication for production of multiplex volume Bragg gratings is described.

The effect of the concentration of chiral compound on 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. It was found that smectic-C liquid crystals containing small amounts of chiral compound showed a large photorefractivity even though they did not exhibit ferroelectricity. The large photorefractivity of the chiral smectic-C phase was attributed to an apearance of the flexoelectric effect.

The creation of self-trapping waveguides within a photopolymer material and the resultant permanent self-written waveguides (SWW) has been investigated for their propagation properties. We look at two light beams as they converge on the photopolymer and interact with the material to produce two separate waveguides fabricated within the material. Here we study these self-written waveguides and investigate their coupling as they propagate within the PVA/AA and combine to form a single SWW within the material. The angle of insertion is interrogated to identify the best angle to produce the SWW coupling effect. The single coupled SWW that is produced, is measured for coherence and attenuation so as to characterize the coupled waveguide.

Organic-inorganic hybrid polymers based on ureasils have found application as waveguides in luminescent solar concentrators and visible light communications. The mechanical properties, and thus processability of ureasils, has previously been qualitatively linked to the chemical structure, but has not yet been studied in detail. In this study, a series of low molecular weight ureasil polymers has been synthesised, and the correlation between the chemical structure and the optical and mechanical properties investigated. A wide-range of techniques are employed to investigate this relationship, including steady-state photoluminescence and Fourier-transform infrared spectroscopy, 4-point flexural testing, and uniaxial tensile testing.

We report on light induced reversible structuring of azobenzene containing polymer films under dynamic changes of the local distribution of the electrical field in the irradiating interference pattern. This is achieved utilizing a homemade setup which consists of three parts: a two-beam interference lithography for topography structuring, an atomic force microscope for in-situ recording (during irradiation) of surface morphology and a diffraction efficiency setup which enables to obtain information about the birefringence grating development simultaneously. Introducing a phase delay between the two interfering beams results in a shift of the whole interference pattern along the sample plane and subsequent change in topographical grating. In this way one can reversibly structure the surface topography in a controlled way and quite fast. On the other hand, this allows to erase the surface grating by just performing half period shift. Combining this method with a single beam exposure creates a very efficient way of completely erasing the birefringence and surface grating.

A new photopolymer system for holographic recording is presented. It exploits the free-radical ring opening polymerization of a cyclic allylic sulfide monomer, 7-methylene-1,5-dithiacyclooctan-3-yl acetate (MDTOA). Such a system allows for the transferring of the sinusoidal holographic pattern with great fidelity, independently on the rigidity of the host matrix. For this purpose, experiments were carried out in a cellulose acetate butyrate (CAB-531-1, Eastman) matrix, using Irgacure 784® as photoinitiating system. The films show excellent optical properties in terms of uniformity and transparency (complete bleaching). The measured diffraction efficiency curves indicate that the written pattern is nearly ideal and it well matches with the theoretical curves computed according to the Kogelnik model. The stability during time of the gratings is monitored and a decrease of efficiency is evident. This means that the formed polymer chains tend to countermigrate smoothing the refractive index modulation. The formation of a crosslinked network is therefore mandatory to obtain stable gratings.

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 instantly 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 substrate and protected on the other side by a cover film. The 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. However for certain applications it is desirable to remove the substrate before or after recording. This will allow the user to make full use of the high flexibility of the photopolymer layer, for example if it comes to curved surfaces that have to be covered. Also more complex stack geometries can be realized in which the photopolymer layer could be embedded in optically well designed cavities or mechanically demanding setups. To facilitate this, we developed Bayfol® HX film grades in which the substrate has a lower adhesion to the photopolymer layer compared to the protective cover film. Therefor the substrate can be removed first in contrast to existing Bayfol® HX film grades which only allow to remove the protective cover film. On the other hand the adhesion of the protective cover film can also be well controlled, so that it can be specifically selected according to the needs of the surface to which the photopolymer layer has to be transferred to. In this paper we demonstrate versatile application processes making use of these transfer grades of Bayfol® HX films with respect to adhesion design, integration in complex stacks and application on curved surfaces.

In interference linear optical displacement sensors, precise position information is provided by the pair of quadrature sine and cosine signals while measuring scales moves along each other. One of these scales is a transmission diffraction grating that combines beam splitter function with phase retardation element. Precalculated parameters of that gratings based not only on diffraction efficiency analysis but phase relations in orders as well, helps to stabilize quadrature signals in the displacement sensor. This paper set the optimization condition in terms of phase shifts of light in diffraction orders influencing phase imbalance. To simulate the conversions of optical radiation by diffraction gratings, a rigorous coupled waves analysis was used. The phase imbalance of the obtained quadrature signals is estimated depending on the uncertainties of influencing parameters.

Dichromated gelatin is a photosensitive material that has been used to make volume holographic elements for over 50 years. The film is an ideal material for many applications in volume holography, such as display technologies and photovoltaic systems. The material has high transparency, low scatter, high index modulation capacity, and has bandwidth broadening processes that can be controlled to extend the angular and spectral bandwidth beyond conventional films. The film is suitable for high-volume production since it is inexpensive and can be manufactured using roll-to-roll techniques. The film consists of gelatin interspersed with light-sensitive ammonium dichromate. After exposing with an interference pattern of light, the film selectively bonds in regions with bright fringes. A hologram is formed after a series of chemical baths removes unbonded chromate from the film and forms a modulation in the index of refraction. Unfortunately, the material has a reputation for inconsistency that has driven many researchers and engineers away from using the material more extensively. While many have commented that it is critical to control the environmental humidity and temperature conditions to achieve consistent hologram formation, little work has been done to systematically address the problem or report findings in literature. In this paper we use data taken from hundreds of hologram samples to quantify the “inconsistency” by measuring the variation in diffraction efficiency and Bragg wavelength. We use a partially controlled facility in which the humidity is controlled during the film drying process, but not in any other stage of the process. We show a strong correlation between drying humidity and repeatability and show that 55-65% drying humidity is optimal. Drying the film at 65% humidity compared to 25% improves the repeatability in both Bragg wavelength and diffraction efficiency by nearly 10X.

We report the trapping of dielectric micro-particles of CaCO₃ via dielectrophoretic forces on the surface of Fe doped LiNbO₃ (LN:Fe) crystal with recorded volume holographic grating which provides quasi-periodic space-charge electric field distribution on the crystal surface. The non-diffracting Bessel beam approach was used for optical induction of holographic grating by 20÷40 mW power Bessel beam at 532 nm wavelength in photorefractive Y-cut LN:Fe crystal providing the Bessel lattice periodicity of ~40 m and hologram size on the crystal surface of 4 mm. This approach provides the induction of high contrast 2D periodic distribution of electric field on the crystal surface and high quality 2D patterning of microparticles. The particles are trapped on the crystal surface in the areas of refractive index maxima of the Bessel lattice. The physical model was developed to explain the experimental results. The photovoltaic approach of trapping and manipulation of micro- and nanoparticles is promising for applications in photonics, integrated optics and biotechnology.

We demonstrate a grating recording method using an excimer KrF UV laser for batch imprinting of distributed feedback (DFB) fiber lasers (FL) with complex profiles and high grating strength (up to K<4 cm^-1) for underwater acoustic sensing applications. The specially developed FPGA-controlled stepping algorithm allows for the recording of long (up to 52mm) DFB laser structures with step error compensation, chirping and apodisation for the FL side-lobe suppression at arbitrarily high exposures. Batch recording involving simultaneous exposure of a number of fibers placed in the recording zone, to achieve time and cost reduction during manufacturing is demonstrated. A number of different gratings in a passive fiber as well as DFB FL in Er-doped active fiber have been fabricated and studied. Further ways to improve the recording process are proposed.

Photosensitive materials and optical information processing technologies based on holographic and photonic techniques are suffering a huge improvement. Furthermore Spatial Light Modulators (SLMs) based on LCoS microdisplays (PALCoS) open new possibilities to modulate the wavefront of a light beam. The improving of the models of the photopolymers as optical recording material together with the modelling of PALCoS, high resolution reflective devices, make possible the generation and recording of Diffractive Optical Elements (DOE) on the photosensitive materials. This DOEs have many important applications in photonics, communications of optical information processing. Working with a setup based on a LCoS display as a master, we can store complex DOEs. We used in this work PVA/AA based on acrylamide with coverplating and index matching system to avoid the influence of the thickness variation on the transmitted light in the material. With the 3-Dimensional diffusion model we can predict the DOE properties before recording and optimize the recording time and the exposure dose. Experimental data is compared with the simulation results to evaluate the accuracy of our model to reproduce the recording of any kind of complex DOE onto a photopolymer. This allows us to choose the appropriate characteristics for the material depending on the application and evaluate the influence of different parameters involved in the DOE generation. In this work we evaluate the simulation of the recording of optical vortexes, axicons, fork gratings and diffractive lenses comparing with the results using our experimental set-up.

We present a study of the diffraction efficiencies of polarization holographic gratings recorded in thin films of the azopolymer PAZO (poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt]). Two series of layers have been prepared using two different solvents – distilled water and methanol. The gratings are inscribed by two plain waves with orthogonal circular polarizations (left and right circular) from a He-Cd gas laser (442 nm) at recording angle 20°, corresponding to grating period 1.3 μm. Higher diffraction efficiency is obtained for the thin film samples spin-coated from the methanol solution for thicknesses below 600 nm. Diffraction efficiency higher than 27% was achieved, as well as surface relief height more than 500 nm.

We explore and discuss the process of PVA/AA fabrication and the doping of the material with a photosensitive dye creating a photosensitive polymer. The dye used is Erythrosine B (EB), which is sensitive to wavelength of λ = 532nm. We expose the photopolymer with the donor wavelength and initiate the self-writing waveguide (SWW) process and polymerization, creating a single homogenous SWW. We investigate the progress of the SWW as it propagates within the photopolymer and map its change in refractive index relative to its surroundings. When the SWW has been completed we then use a multi-mode Y-Coupler to combine two wavelengths λ = 532nm and λ = 625nm. These two light-waves are injected into the SWW via a Y-Coupler test bed. When the combined light-waves beam exits the photo-sensitive polymer it is directed into another MM fiber. Here it is then measured by an optical analyser that investigates the combined optical wavelengths for interference, coherence, wavelength differential group delay (WDRG), non-linear effects and optical loss. We examine the light-waves for modal interference and birefringence and calculate the combined optical power. The optical insertion testing is now revered and a single wavelength is used. The light-wave enters the MM fiber and then the SWW. It then exists and enters the Y-Coupler. Here the wavelength is captured and the coherence testing is undertaken and the optical properties of the wavelength are analysed and a comparison is carried out to investigate the coherence of the light-wave under test.

Spectral methods for the detection and analysis of ionizing radiation sources are widely used in many fields of science and technology. Ecology, geology and mineralogy, metallurgy and the chemical industry, the oil industry and medicine - this is not the whole list of areas where the gamma-ray spectrometer acts as an independent software and hardware tool. Scintillation spectrometers are used to monitor the radiation environment, to search for sources of ionizing radiation, tomography and much more. However, this method is based on the use of vacuum photoelectronic multipliers (PMTs), which complicates the use of devices in the field. This article presents an analysis of gamma-ray scintillation spectrometers built on the basis of silicon photoelectronic multipliers (SiPM). The fields of application of field gamma spectrometers are considered and the basic requirements that the devices must meet to ensure the successful solution of the tasks are determined. The basic principles of the development of field scintillation gamma spectrometers that take into account the processes and transformations of the optical range radiation inside the detector are described. Moreover, the article describes personal experience in the development of an experimental sample of a field gamma spectrometer based on SiPM. In this article, the use of field device refers to any use outside of laboratory conditions.

In this paper, we propose a frequency expanded method based on non-interferometric phase retrieval which can retrieve complex multi-level phase image by using only 1 times Nyquist frequency. Our proposed method utilizes the property of frequency spectrum periodicity and is the unique method with non-interferometry due to the intensity detection directly on the Fourier domain. For a regular phase image, same spacial frequency means same spectrum width. We choose a rectangular window with the same spacial frequency to the phase image and consider normalized Fourier intensity distribution of the rectangular window as the envelope of that of the phase image. After normalizing the spectrum of the phase image, we can expand its Fourier frequency with 1 times Nyquist size to other higher order frequency positions. Therefore, we can generate high-order frequencies artificially from low-order frequency which help us to retrieve phase image accurately and quickly.

Negative-electron-affinity GaAs-based photocathodes have already found widespread application in modern night vision detectors and vacuum electron sources. Considering the importance of surface micro-area analysis for cathode preparation, a new ultrahigh vacuum interconnection system for photocathode preparation and characterization was developed, wherein the scanning focused X-ray imaging positioning technique combined with the X-ray induced secondary electron image was applied to characterize the surface components in the specified micro region of semiconductor photocathodes. With the aid of the advanced characterization technique, the surface components of micro regions of interest for GaAs cathode samples after cleaning and Cs-O activation were analyzed. The experimental results show that the GaAs cathode samples would be subjected to secondary contamination from the metal sheet of sample holder, accompanied by a small amount of sodium and cesium. The subsequent heat treatment and Cs-O activation can hardly remove the sodium contamination, which can affect the arsenic desorption during heat treatment, hinder the Cs-O adsorption in the activation process, and finally reduce the photoemission performance of the activated cathode. Through the application of the X-ray induced secondary electron image, the optimal cleaning method for GaAs cathode was investigated. This surface characterization technique is of practical value to improving analysis accuracy and optimizing the cathode preparation process.