Research Output
1 - 10 of 20
Publication
Influence of dc Pulsed Atmospheric Pressure Plasma Jet Processing Conditions on Polymer Activation
2011-08-23, Dowling, Denis P., O'Neill, Feidhlim T., Langlais, Simon J., Law, Victor J.
Plasma treatments are widely used to activate polymer surfaces prior to adhesive bonding. This study investigates the influence of plasma treatment conditions on the surface activation of a range of polymers using the PlasmaTreat (Open Air) system. In this study the effect of dc pulse plasma cycle time, compressed air flow rate and the plasma jet nozzle to substrate distance on the plasma discharge was examined. The influence that the dc pulse plasma cycle time parameter has on the activation of polypropylene, polystyrene and polycarbonate was also investigated. The level of polymer surface activation was evaluated based on the change in water contact angle after plasma treatment. The polymer surface properties were also monitored using AFM and XPS measurements. The heating effect of the plasma was monitored using both infrared thermographic camera and thermocouple measurements. Plasma diagnostics measurements were obtained using the photo-diode and optical emission spectroscopy techniques. From this study it was concluded that for the PlasmaTreat system the level of plasma activation was closely correlated with the dc pulsed plasma cycle time, which is a measure of the plasma intensity. For example, the more intense plasma obtained with shorter cycle times gave higher levels of polymer activation. The optimized pulsed plasma cycle times were found to be specific for a given polymer type and related to their thermal properties. The pulsed cycle times were also found to correlate with both the substrate and plasma gas temperatures.
Publication
Speckle photography : mixed domain fractional Fourier motion detection
2006-01-01, Patten, Robert, Hennelly, Bryan M., Kelly, Damien P., O'Neill, Feidhlim T., Liu, Ying, Sheridan, John T.
A reflection-based optical implementation of two simultaneous scale-invariant fractional Fourier transforms (FRTs) is used to develop a novel compact speckle photographic system. The system allows the independent determination of both surface tilting and in-plane translational motion from two sequential mixed domain images captured using a single camera
Publication
Temporal analysis of grating formation in photopolymer using the nonlocal polymerization-driven diffusion model
2005-09-05, Kelly, John V., Gleeson, M. R., Close, Ciara E., O'Neill, Feidhlim T., Sheridan, John T., Gallego, Sergi, Neipp, Cristian
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.
Publication
Generalized model of photopolymer behavior for use in optimized holographic data storage scheduling algorithms
2006-10-10, Kelly, John V., Gleeson, M. R., Close, Ciara E., O'Neill, Feidhlim T., Sheridan, John T.
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 data storage : optimized scheduling using the nonlocal polymerization-driven diffusion model
2004-08-01, Sheridan, John T., O'Neill, Feidhlim T., Kelly, John V.
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.
Publication
Effects of absorption and inhibition during grating formation in photopolymer materials
2006-10-01, Gleeson, M. R., Kelly, John V., Close, Ciara E., O'Neill, Feidhlim T., Sheridan, John T.
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.
Publication
Adjusted intensity nonlocal diffusion model of photopolymer grating formation
2002-04-01, Lawrence, Justin R., O'Neill, Feidhlim T., Sheridan, John T.
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.
Publication
Generalized Yamaguchi correlation factor for coherent quadratic phase speckle metrology systems with an aperture
2006-12-01, Kelly, Damien P., Ward, Jennifer E., Gopinathan, Unnikrishnan, Hennelly, Bryan M., O'Neill, Feidhlim T., Sheridan, John T.
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.
Publication
Non-local polymerization driven diffusion based model : general dependence of the polymerization rate to the exposure intensity
2003-08-11, Neipp, Cristian, Beléndez, A., Sheridan, John T., Kelly, John V., O'Neill, Feidhlim T., Gallego, Sergi, Ortuño, M., Pascual, I.
The nonlocal diffusion model proposed by Sheridan and coworkers has provided a useful interpretation of the nature of grating
formation inside photopolymer materials. This model accounts for some important experimental facts, such as the cut-off of diffraction efficiency for high spatial frequencies. In this article we examine the predictions of the model in the case of a general dependence of the polymerisation rate with respect to the intensity pattern. The effects of this dependence on the
different harmonic components of the polymerisation concentration will be investigated. The influence of the visibility on the different harmonic components will also be studied. These effects are compared to the effects of varying RD and σD.
Publication
Thickness variation of self-processing acrylamide-based photopolymer and reflection holography
2001-04, O'Neill, Feidhlim T., Lawrence, Justin R., Sheridan, John T.
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.