Now showing 1 - 10 of 10
  • Publication
    Recording beam modulation during grating formation
    Holography has been of increasing interest in recent years, with developments in many areas such as data storage and metrology. Photopolymer materials provide potentially good materials for holographic recording, as they are inexpensive and self-processing. Many experiments have been reported in the literature that describe the diffraction efficiency and angular selectivity of such materials. The majority of these reports discuss the performance of the holographic optical element after the recording stage. It has been observed, however, that sometimes, during exposure, the transmitted recording beam intensities vary with time. A simple phenomenological model is proposed to explain the beam modulation, which incorporates the growth of the phase grating, time-varying absorption effects, the mechanical motion of the plate, the growth of a lossy absorption grating during the recording process, and the effects of nonideal beam ratios.
      475Scopus© Citations 17
  • Publication
    Holographic data storage : optimized scheduling using the nonlocal polymerization-driven diffusion model
    (Optical Society of America, 2004-08-01) ; ;
    The choice of an exposure schedule that maximizes the uniformity and capacity of a holographic recording medium is of critical importance in ensuring the optimum performance of any potential holographic data storage scheme. We propose a methodology to identify an optimum exposure schedule for photopolymer materials governed by the nonlocal polymerization-driven diffusion model. Using this model, the relationship between the material properties (nonlocality and nonlinearity), the recording conditions and the schedule are clarified. In this way, we provide a first-order comparison of the behavior of particular classes of photopolymer materials for use as holographic storage media. We demonstrate, using the nonlocal polymerization-driven diffusion model, that the exposure schedule is independent of the number of gratings to be recorded and that the optimum schedule may necessitate leaving unpolymerized monomer at the end of the recording process.
    Scopus© Citations 47  334
  • Publication
    Thickness variation of self-processing acrylamide-based photopolymer and reflection holography
    (Society of Photo-Optical Instrumentation Engineers, 2001-04) ; ;
    There are many types of holographic recording material. The acrylamide-based recording material examined here has one significant advantage: it is self-processing. This simplifies the recording process and enables holographic interferometry to be carried out without the need for complex realignment procedures. However, the effect that the polymerization process has on the grating thickness must be examined. This question is fundamental to the material’s use in holographic optical elements, as thickness variations affect the replay conditions of the produced elements. This paper presents a study of this thickness variation and reports for the first time the production of reflection holographic gratings in this material.
    Scopus© Citations 46  546
  • Publication
    Effects of absorption and inhibition during grating formation in photopolymer materials
    Photopolymer materials are practical materials for use as holographic recording media, as they are inexpensive and self-processing (dry processed). Understanding the photochemical mechanisms present during recording in these materials is crucial to enable further development. One such mechanism is the existence of an inhibition period at the start of grating growth during which the formation of polymer chains is suppressed. Some previous studies have indicated possible explanations for this effect and approximate models have been proposed to explain the observed behavior. We examine in detail the kinetic behavior involved within the photopolymer material during recording to obtain a clearer picture of the photochemical processes present. Experiments are reported and carried out with the specific aim of understanding these processes. The results support our description of the inhibition process in an acrylamide-based photopolymer and can be used to predict behavior under certain conditions.
    Scopus© Citations 70  418
  • Publication
    Material kinetics during fabrication of holographic gratings in acrylamide-based photopolymer
    We describe holographic grating formation in Acrylamide-based photopolymer material using the NonLocal Diffusion Driven model & discuss radical suppression leading to an inhibition period before grating growth. Diffusion effects of monomer & polymer are discussed.
      328
  • Publication
    Comparison of holographic photopolymer materials by use of analytic nonlocal diffusion models
    (Optical Society of America, 2002-02-01) ; ;
    The one-dimensional diffusion equation governing holographic grating formation in photopolymers, which includes both nonlocal material response and generalized dependence of the rate of polymerization on the illuminating intensity, has been previously solved under the two-harmonic expansion assumption. The resulting analytic expressions for the monomer and polymer concentrations have been derived and their ranges of validity tested in comparison with the more accurate numerical four-harmonic case. We used these analytic expressions to carry out a study of experimental results presented in the literature over a 30-year period. Automatic fitting of the data with these formulas allows material parameters, including the nonlocal chain-length variance σ, to be estimated. In this way, (i) a quantitative comparison of different materials can be made, and (ii) a standard form of experimental result presentation is proposed to facilitate such a procedure.
      417Scopus© Citations 60
  • Publication
    Adjusted intensity nonlocal diffusion model of photopolymer grating formation
    (Optical Society of America, 2002-04-01) ; ;
    Diffusion-based models of grating formation in photopolymers have been proposed in which the rate of monomer polymerization (removal) is directly proportional to the illuminating intensity inside the medium. However, based on photochemical considerations, the rate of polymerization is proportional in the steady state to the square root of the interference intensity. Recently it was shown that, by introducing a nonlocal response function into the one-dimensional diffusion equation that governs holographic grating formation in photopolymers, one can deduce both high-frequency and low-frequency cutoffs in the spatial-frequency response of photopolymer materials. Here the first-order nonlocal coupled diffusion equations are derived for the case of a general relationship between the rate of polymerization and the exposing intensity. Assuming a twoharmonic monomer expansion, the resultant analytic solutions are then used to fit experimental growth curves for gratings fabricated with different spatial frequencies. Various material parameters, including monomer diffusion constant D and nonlocal variance s, are estimated.
    Scopus© Citations 90  462
  • Publication
    Holographic photopolymer materials : nonlocal polymerization-driven diffusion under nonideal kinetic conditions
    The kinetics of photosensitive polymer holographic recording materials are examined assuming a material that exhibits nonideal kinetic behavior. Previously, a linear relationship between monomer concentration and polymerization was assumed when deriving the nonlocal polymer-driven diffusion (NPDD) model. This is consistent with ideal kinetic conditions in which chain termination is governed by a bimolecular process. However, these models have been reported to disagree with experimental results. In a limiting case of nonideal kinetics it is assumed that primary termination is dominant. In this case the NPDD model must be modified to incorporate a quadratic relationship between the monomer concentration and the polymerization rate. By use of a multiharmonic expansion method of solution the predictions of ideal (bimolecular or linear) and nonideal (primary or quadratic) kinetic models are compared. By using these models we carried out numerical fits to experimental growth curves of gratings recorded in an acrylamide-based cross-linked photopolymer system. Superior fits are achieved by use of the primary termination model. Physical parameters such as the diffusion constant are extracted and compared with results previously reported in the literature.
    Scopus© Citations 105  362
  • Publication
    Temporal analysis of grating formation in photopolymer using the nonlocal polymerization-driven diffusion model
    The nonlocal polymerization-driven diffusion model (NPDD) has been shown to predict high spatial frequency cut-off in photopolymers and to accurately predict higher order grating components. We propose an extension to the NPDD model to account for the temporal response associated with polymer chain growth. An exponential response function is proposed to describe transient effects during the polymerization process. The extended model is then solved using a finite element technique and the nature of grating evolution examined in the case when illumination is stopped prior to the saturation of the grating recording process. Based on independently determined refractive index measurements we determine the temporal evolution of the refractive index modulation and the resulting diffraction efficiency using rigorous coupled wave theory. Material parameters are then extracted based on fits to experimental data for nonlinear and both ideal and non-ideal kinetic models.
    Scopus© Citations 100  384
  • Publication
    Generalized model of photopolymer behavior for use in optimized holographic data storage scheduling algorithms
    A generalized model of photo-polymerization in free radical chainforming polymers has been developed. Applying this model to data storage, optimized scheduling algorithms are developed for the multiplexing of multiple data pages of uniform diffraction efficiency.
      318