The performance of a holographic product for commercial applications depends uniquely on the properties of the material and the skills of the manufacturer to best use and optimize these properties in the design stage and during the various manufacturing steps. The design of the HOE should take into account divers changes in the material that are caused by the process, such as swelling or shrinking of the holographic film, since these determine the spectral characteristics of the HOE. Often the changes are intentionally induced to achieve certain hologram properties, such as wavelength shift of the range of operation, the dependence of the diffraction efficiency on the reconstruction angle, or the desire to influence specific diffraction orders. We report here the results from the evaluation of the holographic properties of HOE in dichromated gelatin. These effects lead to the establishment of force fields and material diffusion throughout the depth of the holographic layer and create a gradient of the mean index of refraction that produces a shift in the angular spectrum. Experimental result for holograms fabricated in DCG and carboxylic polyvinyl alcohol are present and discussed. We report on the development and completion of a facility for continuous layer deposition on plastic substrate, hologram exposure and development.

The thick layered dichromated gelatin synthesis is described and the properties of this light-sensitive material are considered. The schemes of axial speckle-shift hologram and axial 1D hologram are presented. The result of the experiments on recording these types of holograms are discussed. The experiments have confirmed the possibility of multiplexing speckle-shift holograms by shifting the light- sensitive material on the distance equal to the size of the speckle of the reference wave. The experiment has shown that in the case when speckle-shift holograms are multiplexed in a thick-layered gelatin their lifetime decreases as the number of holograms increases. In the case of multiplexing of 1D holograms this decrease of the lifetime is not so pronounced.

THe hologram multiplexing method for the 3D data storage with speckle reference wave is considered. It permits to multiplex holograms by shifting of the speckle wave on the value equal to the its correlation radius. The limit of the number of information units presented by this type of holographics storage exceeds the same value for the spectral or angular multiplexed holograms. However, the system noises reduce it to the regular value. Two different experimental set-ups were tested for the holograms recording: with incident beams and with included beams. It occurred that the number of information units that can be stored in unit volume is larger in the case when both beams possess speckle structures, however the signal-to-noise ratio is also larger in this case, so the spatial modulation of the object beam does not improve the information capacity. Holograms recording was carried out using volume photosensitive medium: newly developed self processing dichromated gelatin of 0.5 mm thickness, and it was compared with the recording in DuPont photopolymer of 100 micron thickness and Fe:LiNbO₃ crystal of 2 mm thickness. The method seems to be very suitable for the laser-disk-memory devices.

In this paper the applications of a photopolymerizable holographic recording material are discussed. The holographic recording characteristics of the photopolymer include very high diffraction efficiency in transmission mode and relatively low exposure energy, typically tens of milliJoules. The recording material has a resolution of 3000 lines/mm and there is not distortion of slanted gratings. This allows high inter-beam angles in transmission recording and makes the material particularly suitable for the holographic recording of diffractive optical elements. The implications of the resolution limit and other material properties for DOE fabrication are discussed in some detail and results for the recording of on- and off-axis focusing and beam splitting diffractive optical elements are presented. One of the most significant advantages of this material is that it is self-developing. As well as making ordinary transmission holography and DOE recording more convenient, this makes the material particularly useful for both live fringe and double exposure holographic interferometry. Live fringes can be viewed as soon as any stress is applied to the object. This material's unique self-developing properties also mean that the growth of the diffraction efficiency of a holographically recorded DOE can be monitored as it is being recorded. This type of on-line control is extremely useful in DOE fabrication particularly when controlling the ratio of beam splitters.

We study the effect of the addition of a crosslinking agent in a photopolymerizable matrix for real time holography. The optimization of the concentration of this component has been realized attending to the holographic parameters like energetic sensitivity and diffraction efficiency. Diffraction efficiencies near to 80 percent have been obtained with energetic exposures of 12 mJ/cm².

Processing of color silver halide holographic materials is still the subject of laboratory studies rather then established technology. Therefore any new approaches to the problem would extend the understanding of the process. the article describes the chemical processing of color holograms recorded on PFG-03C plates that is supposed to be more adequate compared to formerly known ones. The processing employs the experience accumulated during years of work with Russian PE-2, PFG-03 and -03M emulsions and is the application of well known solution physical development to the case of color hologram recording. Once such color hologram is recorded, its optimal reconstruction conditions should be determined for proper color revision. This can be done through the analysis of the angular-spectral selectivity of the hologram.

We report an experimental investigation of recording of slanted fringe holograms in DuPont HRF-800X071-20 photopolymer film under pulse exposure. An initially weak polymerization ability was improved significantly by using incoherent preillumination. The line shape and position of spectral absorbance curves are discussed for a wide range of slant angles.

This paper discusses material behaviors of holographic materials in terms of mechanical, thermomechanical properties and their effects on optical efficiency. Experiments were carried out to characterize coefficient of thermal expansion, stress strain curves, and dynamic mechanical behaviors of photopolymers. It has been found that in-plane deformation of photopolymer has a minimum effect on the diffraction efficiency while out-of-plane deformation can significantly contribute to the diffraction efficiency of holographic optical elements.

In this paper, we report the reliability test results of transmission-type holographic optical elements made with DuPont photopolymer HRF-600. The reliability tests performed in this study include 6000 cycles of liquid-to-liquid thermal shock cycling, 2200 cycles of air-to-air thermal cycling, 1500 hours of humidity test, and 675 hours of burn- in test at 125 degrees C. A total of 210 holograms was tested, with 532 data points collected for efficiency measurements. The results show that the average efficiency change after these tests is negligible and that the standard deviation is only approximately 10 percent.

Automotive holographic head-up display (HUD) systems employing DuPont holographic photopolymer films are presented. Holographic materials for automotive application are exposed to severe environmental conditions and are required high performance. This paper describes the improvement of DuPont photopolymer films for the automotive use, critical technical issues such as optical design, external color and stray light. The holographic HUD combiner embedded in a windshield of an automobile has peculiar problems called external color. Diffraction light from holographic combiner makes its external color tone stimulative. We have introduced RGB three color recording and color simulation in order to improve the external color. A moderate external color tone was realized by the optimization in terms of wavelengths and diffraction efficiencies of the combiner hologram. The stray light called flare arises from a reflection by glass surface of windshield. We have developed two techniques to avoid the flare. First is a diffuser type trap beam guard hologram which reduces the intensity of the flare. Second is the optimization of the design of hologram so that the incident direction of flare is lower than the horizon line. As an example of automotive display a stand-alone type holographic HUD system attached on the dashboard of an automobile is demonstrated, which provides useful driving information such as route guidance. The display has a very simple optical system that consists of only a holographic combiner and a vacuum fluorescent display. Its thin body is only 35 mm high and does not obstruct driver's view. The display gives high contrast and wide image.

Using holographic methods to fabricate antireflection coatings is attractive because arbitrarily small reflectivities may be achieved at a single wavelength with a simple photographic process. In this paper, we discuss the theoretical aspects of these holograms and the technical aspects of fabricating them. We present numerical simulations that predict the spectral response of the coating as a function of the bandwidth of the recording source and the thickness and modulation of the emulsion. These results are confirmed with spectrophotometer measurements of actual coatings. Recording holographic antireflection coatings requires a single collimated light source. The hologram-air interface is sued to create the second wave; this allows the coating to automatically correct for variation in the surface of the hologram. However, this method requires a post recording coating procedure to produce a diffracted wave with the correct phase shift. After the hologram is recorded and processed, a thin layer of SiO₂ or MgF₂ is applied to the hologram to adjust the phase shift between the diffracted wave and the surface reflection. Additionally this coating procedure enhances the durability of the coating and, if MgF₂ is used, lowers the refractive index modulation required for complete cancellation of the surface reflection.

Holographic reflectors with high brightness and excellent environmental stability have been produced using DuPont holographic films. The center wavelength, color bandwidth and viewing cone are defined for the optimal viewing performance. Measurement methods used to quantify holographically enhanced reflective LCD performance are presented. The test results show that holographic reflectors based on the DuPont OmniDex film experienced less than 1 percent brightness degradation under 70 degrees and 95 percent relative humidity for 200 hours, with no measurable color shift. Two examples of how this technology can be extended to enhance color LCDs are also presented.

Dichromated gelatin (DCG) is a commonly used material for recording holographic optical elements. DCG has good optical properties as for example low scattering and high resolution. A photochemical effect causes a change of the refractive index after exposure and development of the DCG- layer. An important parameter for the holographic properties of the DCG-layer, e.g. maximum attainable modulation of the refractive index and swelling of the layer after development, is the concentration of dichromate in the DCG- layer. A further advantage of DCG is the attainable high modulation of the refractive index. In this paper we present experimental results, which give the maximum modulation of the refractive index and the swelling of the DCG-layer as a function of the concentration of dichromate. The results are obtained by analyzing volume phase gratings. The 'coupled wave theory' of Kogelnik gives a formal connection between the modulation of the refractive index and the diffraction efficiency of volume phase gratings. The latter is determined by analyzing the dependance of the diffraction efficiency on reconstruction angle. The exposure energy was varied to attain the maximum modulation of the refractive index for every dichromate concentration. The angular deviation of the Bragg-angle compared with the recording parameters yields the swelling of the DCG-layer. The diffraction gratings were recorded with a holographic copying process. the knowledge of these dependencies is necessary to facilitate optimization of the DCG-layer for different applications of holographic optical elements.

Dichromated poly(acrylic acid) (DCPAA) films with dimethyl formamide (DMF) have ben sued to photofabricate surface relief gratings. The formation of those gratings depends on the self-development time in darkness subsequent to the illumination at a wavelength of 442 nm and is obtained without any chemical treatment or wet processing. The modulation depth of those holographic surface relief gratings and the spatial frequency response of the thin DCPAA-DMF films have been chosen to characterize that self- developing photopolymer system. Those holographic characteristics are presented in this paper.

The quantum efficiency and molar absorption coefficients of dyes are the responsible for holographic efficiency and sensitivity in a photopolymeric holographic recording material. These parameters have been obtained by fitting the experimental transmittance curves as function of time. For this using the mechanism of photo initiation an analytical expression for the transmitted intensity in a photopolymerizable holographic material has been proposed, obtaining good agreement between theory and experience.

A novel method for the characterization of the processing of both absorption and phase holograms was proposed. Differently from the previous models, the square root of the diffraction efficiency of the processed hologram was directly related to the amplitude of the optical density modulation obtained at the development step. This characteristic is a good indicator of the degree of nonlinearity of the hologram processing. While the Lin functions of phase hologram re similar to those of absorption holograms, the shape of the proposed function is completely different. Optical density and diffraction efficiency of holograms recorded in Agfa-Gevaert 8E75HD plates and processed with AAC developer and a solvent bleach without fixation step were measured and used for the demonstration of the method.

We present measurements of complex refractive index changes of new azo dye doped PMMA system, using the so-called Z-scan technique. the photomodulation of the refractive index and absorption coefficients is studied both in steady-state and transient excitation regimes. The saturation intensity in AZD3-PMMA compound is also measured and corresponding corrections are made in obtained Z-scan data. The excitation and relaxation dynamics of the holographic recording are compared with above results. This comparison shows, that the complex refractive index variation (delta) n in AZD3-PMMA is resulted by combination of different excitation modes. However, the (delta) n does not change the sign upon continued exposition. This confirms that the non-monotone growth of holographic diffraction efficiency in this compound is resulted by dynamic saturation of holographic gratings.

A third generation replication machine has been developed to allow mass production of high quality holograms using DuPont holographic recording films. Improved coupling methods of film to the flat-plate masters are described. The operating features and production capabilities of this machine are discussed. An example of a reflection holographic optical element produced using this machine and associated processing equipment are given.

We apply the multilayer rigorous coupled wave theory to analyze reflection gratings in a photorefractive material of an arbitrary thickness. In particular, we study the effect of varying the overall material length over a few thousand grating wavelengths, and also study the effect of layer detuning on reflection grating formation. Furthermore, convergence of the numerical method is rigorously analyzed.

We discussed the kinetics of the photorefractive fundamental space-charge field with phase-modulation at large modulation depth of the interference pattern. When no external field is applied, the influence of large modulation on the corrected modulation function must be considered at low phase- modulation frequency and at small diffusion field. For the drifted case, the corrected modulation function will increase with increase of the external applied field.

During studying anti-humidity of dichromated-gelatin holograms by taking off strongly adsorbing humidity groups of gelatin, the phenomenon that both the amino groups and carboxyl groups of gelatin did participate in chelations with Cr is observed.

The paper presents an analysis of hologram parameters required to obtain highly selective holographic spectral filers, both reflective and transmissive. For two particular cases of spectral filters recorded and operating at the wavelengths of 488 nm and 633 nm grating parameters were analyzed as functions of the recording geometry. The spectral selectivity as a function of layer thickness was also calculated for such holograms. An overview of thick holographic materials suitable for recording of spectral selectors is presented. Experimental results on spectral filters recorded in DuPont photopolymer are discussed.

Measurements are presented for the photorefractive grating recording under pulsed excitation in the crystal of CdTe doped by Fe. The crystal under study is characterized by high electron mobility in comparison with typical value.THe photorefractive parameters of the crystal such as gain factor, Debye screening length, effective density of charge traps as well as effective electro-optic constant have been measured on the basis of gain/grating spacing, gain/crystal rotation angle at different recording beam polarizations, and gain/intensity at different crystal orientations dependencies. The electron-hole competition influence on the crystal photorefractive performance is discussed. The fast photorefractive effect was shown to occur under pulsed excitation maximum gain factor, (Gamma) , being equal to approximately 0.3 cm^-1 without any external electric field. Different self-action effects accompany two-beam coupling are discussed. These are two photon absorption, free carrier generation, self-action of laser beams. The photorefractive effect was separated in its pure form from the various nonlinear optical phenomena.

The performance of a recently developed nonlinear optics epoxy-based polymer with covalently attached dye molecules is investigated. Large refractive nonlinearity is observed. The refractive index nonlinear coefficient and relaxation time were measured using a degenerate two beam coupling scheme with a frequency doubled Nd³⁺:YAG laser. We have used a thin polymer film for dynamic holography recording. Peculiarities of self diffraction at the holograms are discussed for both dynamic and stationary hologram recording. The possibility to write and erase phase gratings reversibly by ns-pulses and store information for hours are demonstrated. An analysis of possible mechanisms for the refractive index nonlinear behavior is presented. The results vividly manifest the possibility of the polymer to be used as reversible medium for information storage. Besides, the polymer structure in question exhibits both ns and quasi-stationary response together with simplicity of fabrication and low prices which have wide prospects for different applications in the field of optical data processing.

Two methods were proposed for protection of holograms against optical copying and against the reconstruction of the model for holographic record. The first method is suitable for the production of master-holograms. It deals with the introduction of different phase inhomogeneities in the object beam with two-exposure technique. Thus a complicated fringe pattern is formed on/before the surface of the object of holographic record. The second method deals with the creation of the parts of the photosensitive media of volume holograms, which thickness differs from the thickness of the rest hologram. These parts have another color than the rest hologram, but in laser light they look black. The procedure of the creation of these marks is concerned with dry process of the OmniDex photopolymers and allows to apply such security marks continuously during the replication of holograms with DuPont's machine.

The present paper is concerned with investigations of image formation properties of As₄₀S₂₀Se₄₀ thin layers. Spectral dependence of the refraction index n of variously treated samples was estimated from optical transmission in the spectral region 400-2500 nm. The n energy dependence of variously treated samples was fitted by the Wemple- DiDomenico dispersion relationship and used to estimate the single-oscillator model parameters. It was found, that exposure, as well as annealing leads to the increase in n values over the all investigated spectral region. Changes of the parameters of the single-oscillator model induced by treatment are discussed on the base of photo- and thermally- induced structural changes, which were directly confirmed by Raman scattering measurements. Such photoinduced structural changes provide good etching selectivity of As₄₀S₂₀Se₄₀ layers in nonaqueous amine based solvents. The best obtained sensitivity values consisted of approximately 40 cm²/J. Surface relief patterns that were fabricated have good surface quality.Diffraction efficiency values of holographic diffraction gratings obtained on the base of As₄₀S₂₀Se₄₀ layers consisted of 60-70 percent.