Now showing 1 - 10 of 20
  • 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.
      391Scopus© Citations 17
  • Publication
    Paraxial speckle-based metrology systems with an aperture
    Digital speckle photography can be used in the analysis of surface motion in combination with an optical linear canonical transform (LCT). Previously [D. P. Kelly et al. Appl. Opt. 44, 2720 (2005)] it has been shown that optical fractional Fourier transforms (OFRTs) can be used to vary the range and sensitivity of speckle-based metrology systems, allowing the measurement of both the magnitude and direction of tilting (rotation) and translation motion simultaneously, provided that the motion is captured in two separate OFRT domains. This requires two bulk optical systems. We extend the OFRT analysis to more general LCT systems with a single limiting aperture. The effect of a limiting aperture in LCT systems is examined in more detail by deriving a generalized Yamaguchi correlation factor. We demonstrate the benefits of using an LCT approach to metrology design. Using this technique, we show that by varying the curvature of the illuminating field, we can effectively change the output domain. From a practical perspective this means that estimation of the motion of a target can be achieved by using one bulk optical system and different illuminating conditions. Experimental results are provided to support our theoretical analysis.
      413Scopus© Citations 22
  • Publication
    Resonances and patterns within the kINPen-MED atmospheric pressure plasma jet
    The kINPen MED atmospheric pressure plasma jet is now undergoing clinical studies that are designed to investigate its suitability as a device for use in plasma medicine treatments. This paper describes dimensionless studies of the synchronizing oscillatory gas flow through the nozzle followed by electro-acoustic measurements coupled with the discharge photo emission. The plasma jet operates in the burst mode of 2.5 KHz (duty cycle = 50%), within a neutral argon Strouhal number of 0.14 to 0.09 and Reynolds number of 3570 to 5370. In this mode the jet acts like a plasma actuator with an anisotropic far field noise pattern that is composed of radiated noise centered at 17.5 kHz; +20 dB, and the expanding visible plasma plume and cooled gas recombine along the jet axial flow (1-2 kHz peak that diminishes at a rate of -1.7 dB.kHz-1).
  • Publication
    Generalized Yamaguchi correlation factor for coherent quadratic phase speckle metrology systems with an aperture
    In speckle-based metrology systems, a finite range of possible motion or deformation can be measured. When coherent imaging systems with a single limiting aperture are used in speckle metrology, the observed decorrelation effects that ultimately define this range are described by the well-known Yamaguchi correlation factor. We extend this result to all coherent quadratic phase paraxial optical systems with a single aperture and provide experimental results to support our theoretical conclusions.
      398Scopus© Citations 13
  • 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
    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
    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.
      469Scopus© Citations 45
  • Publication
    Evaluation of the sensitivity of electro-acousic measurements for process monitoring and control of an atmospheric pressure plasma jet system
    The development of non-invasive process diagnostic techniques for the control of atmospheric plasmas is a critical issue for the wider adoption of this technology. This paper evaluates the use of a frequency-domain deconvolution of an electro-acoustic emission as a means to monitor and control the plasma formed using an atmospheric pressure plasma jet (APPJ) system. The air plasma system investigated was formed using a PlasmaTreat™ OpenAir applicator. Change in the electro-acoustic signal with changes in substrate type (ceramic, steel, polymer). APPJ nozzle to substrate distance and substrate feature size were monitored. The decoding of the electro-acoustic emission yields three sub dataset that are described three separate emission mechanisms. The three emissions are associated with: the power supply fundamental drive frequency and its harmonics; the APPJ nozzle longitudinal mode acoustic emission and its odd overtones, and the acoustic surface reflection that is produced by the impedance mismatch between the discharge and the surface. Incorporating this knowledge into a LabVIEW a program facilitated the continuous deconvolution of the electro-acoustic data. This enabled the use of specific frequency band test limits to control the process the APPJ treatment process which is sensitive to both plasma processing conditions and substrate type and features. PAC Codes: 52.40.Hf, 52.70.-m, 52.77.Fv, 43.60.Vx
      576Scopus© Citations 12
  • 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.
      326Scopus© Citations 33
  • 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.
      307Scopus© Citations 103