Now showing 1 - 10 of 12
  • 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
    Temporal response and first order volume changes during grating formation in photopolymers
    We examine the evolution of the refractive index modulation when recording gratings in an acrylamide based photopolymer. A nonlocal diffusion model is used to predict theoretically the grating evolution. The model has been developed to account for both nonlocal spatial and temporal effects in the medium, which can be attributed to polymer chain growth. Previously it was assumed that the temporal effect of chain growth could be neglected. However, temporal effects due to chain growth and monomer diffusion are shown to be significant, particularly over short recording periods where dark field amplification is observed. The diffusion model is solved using a finite-difference technique to predict the evolution of the monomer and polymer concentrations throughout grating recording. Using independently measured refractive index values for each component of the recording medium, the Lorentz-Lorenz relation is used to determine the corresponding refractive index modulation. The corresponding diffraction efficiency is then determined using rigorous coupled wave analysis. The diffraction efficiency curves are presented for gratings recorded using short exposure times, monitored in real time, both during and after recording. The effect of volume shrinkage of polymer on grating evolution is also examined. Both the nonlocal temporal response of the material and monomer diffusion are shown to influence refractive index modulation postexposure.
      332Scopus© Citations 33
  • 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.
      296Scopus© Citations 99
  • Publication
    Modeling the photochemical effects present during holographic grating formation in photopolymer materials
    The development of a theoretical model of the processes present during the formation of a holographic grating in photopolymer materials is crucial in enabling further development of holographic applications. To achieve this, it is necessary to understand the photochemical and photophysical processes involved and to isolate their effects, enabling each to be modeled accurately. While photopolymer materials are practical materials for use as holographic recording media, understanding the recording mechanisms will allow their limitations for certain processes to be overcome. In this paper we report generalizations of the nonlocal polymer driven diffusion (NPDD) model to include the effects of photosensitive dye absorption and the inhibition effects.
      397Scopus© Citations 59
  • 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
    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
    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.
  • Publication
    Monomer diffusion rates in photopolymer material. Part I. Low spatial frequency holographic gratings
    (Optical Society of America, 2011-03-01) ; ;
    For photopolymers, knowing the rate of diffusion of the active monomer is important when modeling the material evolution during recording in order to understand and optimize their performance. Unfortunately, a confusingly wide range of values have been reported in the literature. Re-examining these results, experiments are carried out for both coverplated (sealed) and uncoverplated material layers and the measurements are analyzed using appropriate models. In this way, a more detailed analysis of the diffraction processes taking place for large-period gratings is provided. These results, combined with those in Part II, provide unambiguous evidence that the monomer diffusion rate in a commonly used acrylamide polyvinyl alcohol-based material is of the order of 10−10 cm2=s. This value closely agrees with the predictions of the nonlocal polymerization-driven diffusion model.
      386Scopus© Citations 49
  • 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.
      343Scopus© Citations 70
  • 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
      898Scopus© Citations 28