High efficiency panchromatic photopolymer recording material for holographic data storage systems

Studies carried out to gauge the potential of a metal-ion doped panchromatic photopolymer recording material for application in real-time holographic data storage is presented. The photopolymer films are spin coated on glass plates to ensure better surface uniformity. Volume holographic transmission gratings with peak diffraction efficiency of 80% could be stored in the photopolymer films of 100 μm thickness. An efficiency of 70% is achievable even for gratings recorded with exposure energy as low as 10 mJ/cm². A checkerboard pattern data page recorded in the photopolymer film using a defocused 4-f recording geometry could be reconstructed with good image quality. The experimental results illustrate the competency of the developed photopolymer for holographic data storage applications.     

Holographic lens recorded on photopolymers: fabrication and study of the image quality

In recent years, holographic optical elements have been introduced in different applications such as high-density data storage, interconnections, spatial and temporal filters and three-dimensional displays. Simultaneously, more sensitive, efficient and durable holographic materials have been developed. Thus it is necessary to analyze the characteristics of these elements in the holographic materials developed. In this paper a method to obtain holographic lenses in a photopolymer is presented. In order to obtain, reconstruct and analyze these lenses, an optical device was designed. Once the holographic lenses are obtained, the device allows us to capture the images provided by these lenses. The imaging quality of these lenses was evaluated by means of the modulation transfer function (MTF) and the contrast. Lenses of different focal lengths were recorded. The holographic lenses obtained had high diffraction efficiency and temporal stability. Moreover, the resolution was greater than that of other lenses with the same diaphragm number.     

Monomer diffusion in sustainable photopolymers for diffractive optics applications

Photopolymers have many applications in optics. However, one of the main drawbacks of these materials is the high toxicity of their components. One of the most widely studied photopolymers is polyvinyl-alcohol/acrylamide, and the carcinogenic potential of acrylamide is well known. In this paper we propose a new sustainable photopolymer as a substitute for acrylamide based photopolymers in the manufacture of diffractive optical elements. Diffraction efficiencies of around 40% were achieved for planar gratings. Monomer diffusion inside this new material was calculated directly for different compositions. Significant differences with acrylamide materials were found.     

Thin-film luminescent concentrators for integrated devices: a cookbook

A luminescent concentrator (LC) is a nonimaging optical device used for collecting light energy. As a result of its unique properties, a LC also offers the possibility of separating different portions of the spectrum and concentrating them at the same time. Hence, LC's can be applied to a whole range of problems requiring the collection, manipulation, and distribution or measurement of light. Further-more, as described in our previous research, thin-film LC elements can be deposited directly over sensor and processing electronics in the form of integrated LC devices. As an aid to further research, the materials and technology required to fabricate these thin-film LC elements through the use of an ultraviolet-curable photopolymer are documented in detail.     

Fast response of the diffraction efficiency in photopolymer prepared by sol–gel process

New photopolymers were designed and prepared using the functionalized triethoxysilane via sol–gel process. They were based on organic–inorganic hybrid materials containing photopolymerizable monomers, photoinitiator, and photosensitizer that is sensitive to the visible light wavelength. The photopolymerization of the diffused monomer in the polymer binder was studied by virtue of infrared spectroscopy. The holographic gratings were successfully fabricated in these sol–gel processed photopolymer samples by conventional optical interference method. We also investigated the effect of sol–gel processed binder on the rate of diffraction behavior. The dynamic behavior of the sol–gel processed photopolymer (SG-PP) was compared with that of the photopolymer (Cell-PP) with the cellulose ester binder.     

Reliability Study of Holographic Optical Elements Made with DuPont Photopolymer

We report reliability-test results of transmission-type holographic optical elements (HOE's) made with the DuPont photopolymer HRF-600. The reliability tests performed include 6000 cycles of liquid-to-liquid thermal-shock cycling (-55 degrees C-125 degrees C), 2200 cycles of air-to-air thermal cycling (-55 degrees C-125 degrees C), 1500 h of humidity testing (85 degrees C and a relative humidity of 85%), and 675 h of burn-in testing at 125 degrees C. A total of 210 holograms was tested, with 532 data points collected for diffraction-efficiency measurements. The results show that the average efficiency change after these tests is in the range of -4% to 0% and the standard deviation is only ~10%.     

Holographic scattering in SiO2 nanoparticle-dispersed photopolymer films

We describe an experimental study of holographic (coherent) scattering due to parasitic noise gratings recorded in SiO2 nanoparticle-dispersed photopolymer films. Dependences of film thickness and nanoparticle concentration on holographic scattering losses are evaluated. It is shown that the geometric feature of the holographic scattering pattern in the two-beam recording setup can be explained by the Ewald sphere construction. It is found that holographic scattering becomes noticeable when a film with nanoparticle concentrations higher than 10 vol.% is thicker than 100 microm. The significance of holographic scattering in the characterization of a volume grating recorded in a thick (>100 microm) nanoparticle-dispersed photopolymer film is also discussed.     

Single-point diamond turning and replication of visible and near-infrared diffractive optical elements

High-fidelity diffractive surfaces have been generated with single-point diamond-turning techniques. A key to the success of this technique is the ability to shape the diamond tool tip to provide the optimum phase-relief profile, given manufacturing constraints. Replication technology is used to transfer the phase-relief surface into a thin epoxy or photopolymer layer on a glass substrate. Diffraction efficiency results for a wide range of zone widths are presented to provide the reader with a baseline of expected performance for replicated visible and near-infrared diffractive optical elements. In addition, a new method for analyzing diffractive surface structures is presented. The ray-trace algorithm quickly provides accurate results of predicted diffraction efficiency for arbitrary zone profiles, which is extremely valuable in predicting manufacturing errors.     

Thermal embossing of mid-infrared diffractive optical elements by use of a self-processing photopolymer master

Surface-relief transmissive diffractive elements were fabricated by embossing. The master was made by lithography with a self-developing photopolymer. The highly cross-linked structure exhibited by the polymer has made possible the direct replication by thermal embossing of polyethylene substrates. Fabricated elements are meant to work with mid-infrared radiation. The influence of some process variables, related to the performance of the diffractive elements, is analyzed.     

Characterization of photopolymerization by a holographic technique applied to a scattering hydrogel

A holographic technique, which consists of writing a phase grating onto a photopolymer layer and recording the time evolution of its diffraction efficiency, is presented for a scattering hydrogel. The influence of photopolymer thickness and writing laser intensity is investigated. Writing parameters that yield maximum diffraction efficiency are determined. A thickness greater than 1/3 of the scattering length results in the diffusion of light in the sample, leading to a decreased diffraction efficiency of the grating. This behavior can be explained by a combination of chemical diffusion and optical scattering. Finally, a calibration of diffraction efficiency with respect to a gel and sol fraction is presented.     

Holographic edge-illuminated polymer Bragg gratings for dense wavelength division optical filters at 1550 nm

We discuss the use of holographic photopolymer materials for use as dense wavelength division multiplexing filters in the C-band of the optical communication spectrum. An edge-illuminated hologram configuration is described that effectively extends the grating length to achieve narrow band filters operating near 1550 nm in photopolymers that are 100-200-microm thick. This configuration enables the formation of apodized and cascaded filter systems. Rouard's method is used to examine the properties of both apodization and cascaded gratings and indicates the potential for narrow spectral bandwidths (< 0.2 nm) and high side-lobe suppression (<-- 30 dB). Initial experimental results with a commercially available photopolymer are provided that verify narrowband spectral-transmittance properties (< 0.6 nm) and the ability to apodize the index profile. The primary limitation of the design is the absorption of existing photopolymer materials. Optimizing the polymer chemistry for filter design at 1550 nm may solve this problem.     

Investigation on the panchromaticity of silver-doped poly(vinyl alcohol)/acrylamide photopolymer

An investigation on the panchromaticity of a silver-doped poly(vinyl alcohol)/acrylamide photopolymer system is presented in this paper. Frequency-doubled Nd:YAG (532 nm) and Ar? (488 nm) lasers were used for the characterization of the films. Previous studies using an He-Ne laser (632.8 nm) showed that plane-wave transmission grating with a high diffraction efficiency of 75% could be stored in the optimized film. From the present study, it was noted that transmission gratings with 70% diffraction efficiency could be recorded using Ar? and Nd:YAG lasers, thereby elucidating the possibility of using the developed photopolymer system as a competent panchromatic recording medium.     

Electrochromic and optical study of atmospheric pressure chemical vapour deposition MoO3-Cr2O3 films

Electrochromism (EC) is a phenomenon in which materials are able to change their optical properties in a reversible and persistent way under the action of a voltage pulse. The studied MoO3-Cr2O3 films are obtained by atmospheric pressure CVD. Mixing MoO3 films with Cr2O3 is expected to enhance optical transparency and to modulate electrochromic properties of MoO3 films. In the present work, the study is focused on the morphological, structural and optical properties of MoO3-Cr2O3 films as a function of annealing temperatures. Raman spectroscopy and optical spectrophotometry are used for the film characterization. The mixed oxide films obtained on ordinary glass substrates show transmittance values in the range of 70-80%. Surface morphology is analyzed by SEM and AFM methods. The microanalysis of MoO3-Cr2O3 films reveals uniform distribution of the elements, which is a sign of homogeneous structure.     

Copying low spatial frequency diffraction gratings in photopolymer as phase holograms

Abstract

Photopolymers are studied as holographic recording materials for recording computer-generated phase holograms. The recording was performed using a holographic copying process, in which the master is produced by means of a high resolution graphic device. To our knowledge it is the first time a photopolymer has been used to obtain copies with this technique. As it does not work in real time, it is possible to store the diffractive optical element for a long time because the dye is finished during exposition and no wet processing is needed after exposition. The photopolymer used in these experiments was composed of acrylamide and triethanolamine as the co-initiator, photo-initiated with a dye, yellow eoxine. Components were supported by a film of poly-(vinylalcohol) (PVA). The resulting thickness of the film was 70 & plusmn; 5 μm, symmetrical and asymmetrical diffraction gratings were obtained as phase holograms by index and thickness modulation, monitored with an electron microscope, and the low spatial frequency response of the photopolymer was studied. Diffraction efficiency achieved for copied gratings was about 30%. With this study we get a complete characterization of the photopolymer for the full range of the typical spatial frequencies that can be recorded with the high resolution graphic device used.     

Effect of zeolite nanoparticles on the optical properties of diacetone acrylamide-based photopolymer

The effect of zeolite nanoparticles with BEA type framework structure on the optical properties of a diacetone acrylamide (DA)-based holographic photopolymer has been investigated. Both types of zeolite nanocrystals, as synthesized (BEA) and silver containing (BEA-Ag), are used for doping the DA photopolymer. Doping of the DA photopolymer with BEA zeolites results in an 11% decrease of the average refractive index of the nanocomposite layer, while the inclusion of BEA-Ag nanoparticles decreases the average refractive index by 3% only. This observation is in good agreement with the fact that the contrast in refractive index between the host photopolymer and nanoparticles is expected to be much lower for the BEA nanoparticles containing Ag in their pores. Doping of the DA photopolymer with pure BEA zeolite nanoparticles results in a significant increase in refractive index modulation due to holographic recording, Δn, of up to 91% at a concentration of 2 wt.% compared to un-doped layers. For the BEA-Ag zeolites, a maximum increase in Δn of up to 17% at a concentration of 0.5 wt.% is observed. The increase in Δn is attributed to the difference in n between the host photopolymer and nanoparticles and the redistribution of the nanoparticles during holographic recording. It is demonstrated that the DA photopolymer is compatible as a host material for the porous BEA nanoparticles. This is due to the large size of the DA monomer molecules, which restricts monomer migration into the zeolite pores and thus the pores of the Ag-free BEA nanoparticles remain empty, making them suitable for application in holographic sensors.     

Optical discrepancy in the mosaic texture of NOA65 photopolymer transfer printed using phase-separated PS/PMMA surface structures treated with cyclohexane

In this paper, we studied the physical and optical properties of the mosaic-textured surface of NOA65 photopolymer transfer printed indirectly using thin layers of phase-separated PS/PMMA blend. The immiscible, phase-separated PS/PMMA blend was spin-coated onto a glass surface and treated with cyclohexane to form the mosaic texture, then the texture was used to transfer print onto UV-curable NOA65 photopolymer with PDMS used as an indirect transfer bridge. The PS/PMMA membrane had three phase-separated sub-thin layer structures: the top PS-rich layer, the interlayer PS/PMMA blend, and the underlying PMMA-rich layer. Using a selective solvent (cyclohexane), the PS phase of the membrane surface was dissolved to form the mosaic structure. By transfer printing the mosaic structures of different textures indirectly onto NOA65, three varieties of surface structure were formed: Non-continuous mosaic textures, smooth surfaces with many interior indentations, and more obvious mosaic structures. The NOA65 photopolymer not only has favorable elasticity, rendering it rollable and malleable, but our experimental observations also revealed that as there are samples with 60% PS and samples with 40% PMMA, transfer printing onto the more evenly distributed mosaic texture on the NOA65 surface enabled it to have self-cleaning effects, such as hydrophobicity and not easily attracting dust (the so-called lotus effect) as well as possessing high optical transmittance, and low reflectance with minimal HAZE value (HAZE value often is expressed as clarity). These features can be applied to many common optical components such as screens or glass display cabinets.     

Three-dimensional optical data storage in a fluorescent dye-doped photopolymer

We propose a new, to our knowledge, monolithic multilayer optical storage medium in which data may be stored through the diffusional redistribution of fluorescent molecules within a polymer host. The active portion of the medium consists of a photopolymer doped with a fluorescent dye that is polymerized at the focal point of a high-numerical-aperture lens. We believe that as fluorescent molecules bond to the polymer matrix they become more highly concentrated in the polymerized regions, resulting in the modulated data pattern. Since data readout is based on detection of fluorescence rather than index modulation as in other photopolymer-based memories, the problems of media shrinkage and optical scatter are of less concern. An intensity threshold observed in the recording response of this material due to the presence of inhibitor molecules in the photopolymer allows for the three-dimensional confinement of recorded bits and therefore multilayer recording. The nonlinear recording characteristics of this material were investigated through a simple model of photopolymerization and diffusion and verified experimentally. Both single-layer and multilayer recordings were demonstrated.     

Narrow-bandwidth holographic reflection filters with photopolymer films

Narrow-bandwidth holographic reflection filters are demonstrated that use volume gratings in 100-mum-thick photopolymer films. A full width at half-maximum of 0.09 nm can be achieved with ~35% peak reflectance near the 900-nm region. Detailed fabrication procedures and filter performances are described.     

Investigation of the substrate effect for Zr doped ZnO thin film deposition by thermionic vacuum arc technique

ZnO is a fundamental wide band gap semiconductor. Especially, doped elements change the optical properties of the ZnO thin film, drastically. Doped ZnO semiconductor is a promising materials for the transparent conductive oxide layer. Especially, Zr doped ZnO is a potential material for the high performance TCO. In this paper, ZnO semiconductors were doped with Zr element and microstructural, surface and optical properties of the Zr doped ZnO thin films were investigated. Zr doped ZnO thin films were deposited thermionic vacuum arc (TVA) technique. TVA is a rapid and high vacuum deposition method. A glass, polyethylene terephthalate and Si wafer (111) were used as a substrate material. Zr doped ZnO thin films deposited by TVA technique and their substrate effect investigated. As a results, deposited thin films has a high transparency. The crystal orientation of the films are in polycrystal formation. Especially, substrate crystal orientation strongly change the crystal formation of the films. Substrate crystal structure can change the optical band gap, microstructural properties and deposited layer formation. According to the atomic force microscopy and field emission scanning electron microscopy measurements, all deposited layer shows homogeneous, compact and low roughness. The band values of the deposited thin film were approximately found as to be 3.1–3.4 eV. According to the results, Zr elements created more optical defect and shifted to the band gap value towards to blue region.     

CuNiSi溅射薄膜热性能与溅射靶材中稀土元素加入量之间关系的研究

应用光热辐射和光学速反射的方法了靶材中Ｌａ系混合稀土元素加入量对ＣｕＮｉＳｉ溅射薄膜热性能的影响。靶材中Ｌａ系混合稀土元素的加入引起被溅射薄膜热行为的差异,随着靶材料中Ｌａ系稀土元素加入量的提高,被溅射的ＣｕＮｉＳｉ薄膜的热扩散系数α也增加。