Now showing 1 - 10 of 20
  • 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
    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
    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.
      394Scopus© Citations 59
  • 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.
      294Scopus© Citations 99
  • Publication
    Nonlocal photopolymerization kinetics including multiple termination mechanisms and dark reactions. Part I. Modeling
    (Optical Society of America, 2009-09-01) ;
    The photochemical processes present during free-radical-based holographic grating formation are examined. A kinetic model is presented, which includes, in a more nearly complete and physically realistic way, most of the major photochemical and nonlocal photopolymerization-driven diffusion effects. These effects include: (i) nonsteady-state kinetics (ii) spatially and temporally nonlocal polymer chain growth (iii) time varying photon absorption (iv) diffusion controlled viscosity effects (v) multiple termination mechanisms, and (vi) inhibition. The convergence of the predictions of the resulting model is then examined. Comparisons with experimental results are carried out in Part II of this series of papers [J. Opt. Soc. Am. B 26, 1746 (2009)].
      529Scopus© Citations 99
  • 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.
      546Scopus© Citations 42
  • 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.
      462Scopus© Citations 31
  • 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.
      392Scopus© Citations 17