高效率复合同轴全息透镜的研制

提出一种复合同轴全息透镜的设计制作方法。该设计方法采用两片离轴全息透镜复合,按使用情况在布喇格条件下进行消像差设计。制作的全息透镜具有衍射效率高和像差小的特点,适合任意给定再现波长的窄带光场合。实验研制了一个全息透镜,其再现衍射效率达到63% 。     

Silver halide sensitized gelatin holograms in Slavich PFG-01 red-sensitive emulsion

Abstract

Silver halide sensitized gelatin (SHSG) is an interesting technique for the production of holographic optical elements. It combines the high sensitivity of photographic emulsions with the well-known low scattering and high diffraction efficiency corresponding to dichromated gelatin. In this paper we describe SHSG holograms recorded on Slavich PFG-01 emulsions. We will show that real high diffraction efficiencies can be obtained (as high as 93% allowing for reflections) when using this material for recording phase transmission holograms. The influence of the bleach bath temperature and a hardening bath in the processing was studied and the procedure was optimized for these two parameters. Our investigations reveal that PFG-01 emulsion is not only a substitute for Agfa material, but also offers better results, at a moment in which Agfa has stopped its production of holographic material.     

Non-hydroscopic vanilla doped dichromated gelatin holographic material

Dichromate gelatins are well-known holographic materials. By doping this material with synthetic vanilla a change in the spectral response from regular dichromate gelatin is observed as an increase in optical density. This mixture presents an unusual high humidity resistance. It was possible to record holographic diffraction gratings using an argon ion laser (λ=488 nm). These gratings exhibit good diffraction efficiency in transmission, on the order of 60% at Bragg angle, with more than 1700 lines/mm spatial resolution. The material development process consists simply of dipping it into using a solution of water and isopropyl alcohol. A hypothesis on the hydroscopic response of this new photosensitive material is also presented.     

Stabilization of volume gratings recorded in polyvinyl alcohol-acrylamide photopolymers with diffraction efficiencies higher than 90%

Abstract

Obtaining holographic volume gratings with high diffraction efficiencies that can be used under white light has been a serious problem for the polyvinyl alcohol-acrylamide-based photopolymers developed by other researchers. In this paper we propose to eliminate the residual monomer in order to stabilize the holographic gratings. The residual dye and residual monomer are the main problems in achieving high diffraction efficiencies stable under white light. In order to polymerize the residual monomer we illuminate the gratings with coherent green light and incoherent white light and we heat the grating at 80°C for different times. We also study the conservation of gratings dried in critical conditions of humidity and temperature. After stabilization the diffraction efficiencies achieved were clearly higher than 90%.     

Formation of anisotropic diffraction gratings in a polymer-dispersed liquid crystal by polarization modulation using a spatial light modulator

Anisotropic diffraction gratings based on a holographic polymer-dispersed liquid crystal (HPDLC) are realized by interferometric exposure using a spatial light modulator (SLM). The SLM is used in the HPDLC grating formation for anisotropic holographic recordings of two-dimensional polarization states for an incident light beam. The diffraction efficiency for P-polarization and the distinctive ratio of diffraction efficiency in P-polarization to that in S-polarization increases with the signal level applied to the SLM. The resulting volume gratings exhibit diffraction efficiency of more than 60% and a distinctive ratio of diffraction over 100. The microscopic origin of the anisotropic property is investigated by an optical polarizing microscope. The novel characteristics of the anisotropic diffraction properties of HPDLC are applied to an image reconstruction technique.     

Holographic sensor for water in solvents

The diffraction color of a gelatin holographic diffraction grating changed as a function of the water activity when immersed in a "wet" hydrophobic liquid. Quantification of the absorption maximum of the diffracted light showed that it was related, after calibration, to either the water content or the water activity of the solvent. The holographic diffraction grating measured water contents of hydrocarbon solvents at sensitivities comparable to that of the Karl Fischer coulometric titrator and over a wide range of water contents. A grating immersed in xylene revealed a visible color change when the water content was increased from 47 to 120 ppm. Conversely, the holographic grating responded to ethanol in water in the range 0-1% (w/w). The inexpensiveness and simplicity of silver halide holographic reflection gratings, combined with their relatively high sensitivity, suggests that these devices might find widespread application as immersible water activity sensors for hydrophobic liquids.     

Silver Halide (Sensitized) Gelatin in Agfa-Gevaert Plates: The Optimized Procedure

Abstract

Silver halide sensitized gelatin (SHSG) is one of the most promising techniques for the fabrication of transmission holographic optical elements, achieving relatively high sensitivity of photographic material with the low scattering and high light stability of dichromated gelatin. In this paper we present the optimized procedure in Agfa-Gevaert plates. Diffraction gratings with a diffraction efficiency up to 80% and a noise level of less than 1% are obtained with a sensitivity 10³ times better than dichromated gelatin.     

Deformed-Helix Ferroelectric Liquid-Crystal Spatial Light Modulator that Demonstrates High Diffraction Efficiency and 370-Line Pairs/mm Resolution.

New liquid-crystal media and photoconductor materials are being utilized in spatial light modulators to increase their resolution, diffraction efficiency, speed, and sensitivity. A prototypical device developed for real-time holography applications has shown an 8% diffraction efficiency from a holographic grating with a spatial frequency of 370 line pairs/mm (lp/mm). At 18 lp/mm the device has demonstrated a 31% diffraction efficiency with a 600-mus hologram write time using 400-nJ/cm(2) write beams.     

Trithiocarbonate-mediated free-radical photopolymerization: improved uniformity in hologram recording

A holographic material based on a photopolymerizable nematic acrylate was improved by the addition of the trithiocarbonate, EtO2CCH2SC(S)SCH2CO2Et, increasing uniformity and reproducibility in the formation of electrically switchable holographic gratings. Diffraction efficiencies as high as 34%, the thin-grating theoretical maximum, were achieved at large (10-14 microm) grating spacings. Improved diffraction efficiency was seen over a range of grating spacings (0.35-10 microm). The exposure window for grating formation was increased by an order of magnitude, resulting in much improved reproducibility.     

Polarization of holographic grating diffraction. I. General theory

The full polarization property of volume holographic grating diffraction is investigated theoretically. With a simple volume grating model, the diffracted fields and Mueller matrices are first derived from Maxwell's equations by using the Green's function algorithms. The formalism is derived for the general case that the diffraction beam and the grating wave vector are not in the plane of incidence, where s waves and p waves are not decoupled. The derived photon-momentum relations determine the Bragg angle selectivity. The parameters of diffraction strength related to the hologram-writing process and material are defined and are not necessarily small in general. The diffracted-beam profiles are analytically calculated by using the known grating shape function. This theory has provided a fundamental understanding of the polarization phenomena of a real holographic diffraction grating device. The derived algorithm would provide a simulation-analysis tool for the engineering design of real holographic beam combiner/splitter devices.     

Implementation of a spatially multiplexed pixelated three-dimensional display by use of a holographic optical element array

A pixelated holographic stereogram is proposed and experimentally studied for the emulation of a spatially multiplexed composite three-dimensional (3-D) pixel display. With this approach, pixelated holograms are utilized to compose spatially multiplexed images. Each composite pixel in the holographic optical element array has a diffraction pattern that scatters light into predefined spatial directions. Under reconstruction, each pixel generates different intensities along a range of viewing angles. When the composite holographic pixel array is assembled, it has the capability to deliver 3-D effects. The technique, together with a novel recording scheme that is designed to synthesize a computerized 3-D display system based on this concept, is described in some detail.     

Efficient holographic recording in novel azo-containing polymer

We report on periodic structures inscribed through holographic recording by both intensity light patterns and polarization patterns in novel azo-containing polymer poly[oxyethylene({6-[4-(biphenyl-4-azo)phenoxy]hexyl}imino) ethylene-carbonylimino(2-methyl-1,3-phenylene)iminocarbonyl] abbreviated as A-TDI. The kinetic of grating recording and diffraction efficiency of recorded gratings using polarized cw Ar⁺ laser light have been measured for s–s, p–p and s–p polarization configurations. The translation grating technique applied during the light self-diffraction process allowed for investigations of phase and amplitude gratings contributions to light diffraction in the studied polymer. Full reversibility of polarization (s–p) grating recording and observation of a half-period structure development during optical erasure process makes this material a good candidate for further studies as a potential material for dynamic holography purposes.     

全息警戒系统的研制

利用全息技术，研制了成旋转全息圆盘，并与微机结合，开发出了一种体积小、性能高的室内警戒系统。使用不可见激光束垂直投射到旋转全息圆盘上，产生复数衍射光束向不同方向传播。人或物体上的反射散乱光经全息圆盘收集，菲涅尔透镜聚集，通过光电转换器送入微机处理判别，在约１０平方米的警戒区域内，能够快速监测出入的存在及其移动情况。     

Effect of dopant composition ratio on nonvolatile holographic recording in LiNbO3:Cu:Ce crystals

The effect of dopant composition ratio on nonvolatile holographic recording in LiNbO3:Cu:Ce crystals is investigated experimentally. The results show that the dopant composition ratio affects the recording sensitivity and fixed diffraction efficiency by altering the UV light absorption characteristics of the crystals during nonvolatile, holographic recording. Increasing the dopant composition ratio of Cu and Ce leads to an increase in the absorption of UV light and further to an increase in the recording sensitivity and fixed diffraction efficiency. The UV light absorption characteristics of LiNbO3:Cu:Ce crystals and their roles in nonvolatile holographic recording are theoretically analyzed. The theoretical results are consistent with those of the experiments.     

Holographic patterning of luminescent photopolymer nanocomposites

Volume phase gratings in the photopolymerisable composites, containing luminescent nanoparticles have been fabricated for the first time. Nanoparticles of LaPO₄, doped by Ce³⁺ and Tb³⁺ ions (the trade name is REN-X-green) with high luminescence quantum yield were used as a luminescent inorganic additive. The holographic gratings in such materials are formed as a result of the diffusion distribution of the nanoparticles during exposure of photopolymerisable composites to interference pattern. The influence of the pre-polymer formulation and the holographic patterning parameters on the grating formation is comprehensively investigated. The use of the optimised pre-polymer syrup containing two monomers with sufficiently different polymerisation rates allows fabrication of gratings with diffraction efficiency up to 80% at low optical losses (< 5%) (20 μm film thickness). To obtain maximum diffraction efficiency the intensity and the period of the interference pattern were optimised for each formulation. In addition maximum diffraction efficiency was achieved with the nanocomposites containing 30–32 wt.% of nanoparticles. On the other hand the highest possible modulation of the nanoparticles' concentration was obtained for the concentration of about 20 wt.%. In this case maximum ordering of the nanoparticles in the polymer matrix is achieved. The photoluminescence of the nanoparticles within the homogeneous polymer film and within the grating has been measured. The example application of the photopolymerisable composite containing luminescence inorganic nanoparticles in holographic security technology has been demonstrated.     

Optimization of a thick polyvinyl alcohol-acrylamide photopolymer for data storage using a combination of angular and peristrophic holographic multiplexing

The capability of polyvinyl alcohol-acrylamide photopolymer materials to obtain angularly multiplexed holographic gratings has been demonstrated [Appl. Phys. B 76, 851 (2003)]. A combination of two multiplexing methods--peristrophic and angular multiplexing--is used to record 60 holograms. An exposure schedule method is used to optimize the capability of the photopolymerizable holographic material and obtain holograms with a higher, more uniform diffraction efficiency. In addition, because of this exposure schedule method, the entire dynamic range (M#) of the material will be exploited, obtaining values of approximately M# approximately 9 in layers approximately 800 microm thick.     

Determination of threshold exposure and intensity for recording holograms in thick green-sensitive acrylamide-based photopolymer

For optical data storage applications, it is essential to determine the lowest intensity (also known as threshold intensity) below or at which no data page or grating can be recorded in the photosensitive material, as this in turn determines the data capacity of the material. Here, experiments were carried out to determine the threshold intensity below which the formation of a simple hologram--a holographic diffraction grating in a green-sensitized acrylamide-based photopolymer--is not possible. Two main parameters of the recording layers--dye concentration and thickness--were varied to study the influence of the density of the generated free radicals on the holographic properties of these layers. It was observed that a minimum concentration per unit volume of free radicals is required for efficient cross-linking of the created polymer chains and for recording a hologram. The threshold intensity below which no hologram can be recorded in the Erythrosin B sensitized layers with absorbance less than 0.16 was 50 μW/cm(2). The real-time diffraction efficiency was analyzed in the early stage of recording. It was determined that the minimum intensity required to obtain diffraction efficiency of 1% was 90 μW/cm(2), and the minimum required exposure was 8 mJ/cm(2). It was also determined that there is an optimum dye concentration of 1.5 × 10(-7) mol/L for effective recording above which no increase in the sensitivity of the layers is observed.     

Improvement of sensitivity and refractive-index changes in LiNbO3:Ce:Cu crystals with UV light

A nonvolatile recording scheme is proposed using LiNbO₃:Ce:Cu crystals and modulated UV light to record gratings simultaneously in two centres and using red light to bleach the grating in the shallow centre to realize persistent photorefractive holographic storage. Compared with the normal UV-sensitized nonvolatile holographic system, the amplitude of refractive-index changes is greatly increased and the recording sensitivity is significantly enhanced by recording with UV light in the LiNbO₃:Ce:Cu crystals. Based on jointly solving the two-centre material equations and the coupled-wave equations, temporal evolutions of the photorefractive grating and the diffraction efficiency are effectively described and numerically analysed. Roles of doping levels and recording-beam intensity are discussed in detail. Theoretical results confirm and predict experimental results.     

Real-time and postprocessing holographic effects in dichromated pullulan

Experimental results concerning both real-time and postprocessing (after-development) behavior of a novel photosensitive material, dichromate-sensitized pullulan (DCP), are investigated. The exposure mechanism and possibilities for controlling holographic grating properties are discussed. We have shown that it is possible to maximize the diffraction efficiency of interference gratings after development by controlling diffraction efficiency in real time. Stronger real-time effects of DCP compared with those of dichromated gelatin are achieved.     

Polarization holographic high-density optical data storage in bacteriorhodopsin film

Optical films containing the genetic variant bacteriorhodopsin BR-D96N were experimentally studied in view of their properties as media for holographic storage. Different polarization recording schemes were tested and compared. The influence of the polarization states of the recording and readout waves on the retrieved diffractive image's intensity and its signal-to-noise ratio were analyzed. The experimental results showed that, compared with the other tested polarization relations during holographic recording, the discrimination between the polarization states of diffracted and scattered light is optimized with orthogonal circular polarization of the recording beams, and thus a high signal-to-noise ratio and a high diffraction efficiency are obtained. Using a He-Ne laser (633 nm, 3 mW) for recording and readout, a spatial light modulator as a data input element, and a 2D-CCD sensor for data capture in a Fourier transform holographic setup, a storage density of 2 x 10(8) bits/cm2 was obtained on a 60 x 42 microm2 area in the BR-D96N film. The readout of encoded binary data was possible with a zero-error rate at the tested storage density.