Now showing 1 - 10 of 20
  • 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.
  • Publication
    Holographic grating evolution in photopolymer materials
    A generalized non-local polymerization driven diffusion (NPDD) model is presented, including the effects of absorption and inhibition. Experimentally obtained growth curves are fit using a four-harmonic numerical fitting algorithm and key material parameters are extracted.
  • Publication
    Extended model of the photoinitiation mechanisms in photopolymer materials
    (American Institute of Physics, 2009-11) ; ; ;
    In order to further improve photopolymer materials for applications such as data storage, a deeper understanding of the photochemical mechanisms which are present during the formation of holographic gratings has become ever more crucial. This is especially true of the photoinitiation processes, since holographic data storage requires multiple sequential short exposures. Previously, models describing the temporal variation in the photosensitizer (dye)concentration as a function of exposure have been presented and applied to two different types of photosensitizer, i.e., Methylene Blue and Erythrosine B, in a polyvinyl alcohol/acrylamide based photopolymer. These models include the effects of photosensitizer recovery and bleaching under certain limiting conditions. In this paper, based on a detailed study of the photochemical reactions, the previous models are further developed to more physically represent these effects. This enables a more accurate description of the time varying dye absorption, recovery, and bleaching, and therefore of the generation of primary radicals in photopolymers containing such dyes.
    Scopus© Citations 31  543
  • Publication
    The approximate model for holographic grating formation in photopolymers
    (Optical Society of America, 2006-10-10) ; ; ;
    Nonlocal Polymerisation Driven Diffusion model describes grating formation in photopolymer materials and gives valuable insight into the processes taking place during formation. For weak exposures, NPDD reduces to a simple approximate model describing polymer concentration
  • Publication
    Monomer diffusion rates in photopolymer material: Part I. Low spatial frequency holographic gratings: reply
    (Optical Society of America, 2012-03) ; ;
    In [1,2] an error (by a factor of 1000) in the diffusion rate of monomer in a photopolymer material used by the authors of [3], is presented. In [3] no errors are identified in our analysis and our physical evidence is not addressed. It is implied that our model and our results are disproven by the results in the papers referenced in [3]. In fact these papers do not provide any such quantitative evidence. The observations made regarding the significance of the authors’ contributions, in particular the validity of their model and the practical importance of their material are also discussed.
    Scopus© Citations 4  608
  • 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  381
  • Publication
    Nonlocal photopolymerization kinetics including multiple termination mechanisms and dark reactions. Part II. Experimental validation
    (Optical Society of America, 2009-08-19) ; ; ;
    In the first of this series of papers [J. Opt. Soc. Am. B 26, 1736 (2009)], a new kinetic model, which includes most of the major photochemical and nonlocal photopolymerization driven diffusion effects, was proposed. Predictions made using the model were presented, and the numerical convergence of these simulations were examined when retaining higher-concentration harmonics. The validity and generality of the model is examined by applying it to fit experimental data for two different types of photopolymer material appearing in the literature. The first of these photopolymer materials involves an acrylamide monomer in a polyvinylalcohol matrix. The second is a more complex photopolymer in an epoxy resin matrix. Using the new model, key material parameters are extracted by numerically fitting experimentally obtained diffraction efficiency growth curves. The growth curves used include data captured both during exposure and post-exposure, allowing examination and analysis of "dark reactions".
      541Scopus© Citations 76
  • Publication
    Examination of the photoinitiation processes in photopolymer materials
    (American Institute of Physics, 2008-09) ; ; ;
    Holographic data storage requires multiple sequential short exposures. However, the complete exposure schedule may not necessarily occur over a short time interval. Therefore, knowledge of the temporally varying absorptive effects of photopolymer materials becomes an important factor. In this paper, the time varying absorptive effects of an acrylamide/polyvinylalcohol photopolymer material are examined. These effects are divided into three main photochemical processes, which following identification, are theoretically and experimentally examined. These processes are (i) photon absorption, (ii) photosensitizer recovery, and (iii) photosensitizer bleaching.
    Scopus© Citations 42  609
  • 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.
      471Scopus© Citations 17
  • Publication
    Monomer diffusion rates in photopolymer material : Part II High-frequency gratings and bulk diffusion
    (Optical Society of America, 2011-04-01) ; ; ;
    Photosensitive polymers are of practical importance, and mass transport within such materials plays a critical role in their behavior. Building on the work in Part I [J. Opt. Soc. Am. B doc. ID 136413 (posted 5 January 2011, in press)], the diffusion constants of a number of materials (i.e., acrylamide, polyacrylamide, water, propanol, and acetone) within a photosensitive layer are measured. A combination of optical and physical chemistry techniques is applied under different conditions. Determining the rates of diffusion is beneficial as it: (i) indicates material stability over time and (ii) supports material characterization, modeling, and performance optimization
      948Scopus© Citations 30