Results from the investigation of the diffusion processes in a dry acrylamide-based photopolymer system are presented. The investigation is carried out in the context of experimental work on optimization of the high spatial frequency response of the photopolymer. Tracing the transmission holographic grating dynamics at short times of exposure is utilized to measure diffusion coefficients. The results reveal that two different diffusion processes contribute with opposite sign to the refractive index modulation responsible for the diffraction grating build up.Monomer diffusion from dark to bright fringe areas increases the refractive index modulation. It is characterized with diffusion constant D 0 =1.6.10 -7 cm 2 /s. A second diffusion process takes place during the recording. It decreases the refractive index modulation and we ascribe it to diffusion of short chain polymer molecules and/or radicals from bright to dark fringe areas. The estimated diffusion coefficient for this process is D 0 = 6.35.10 -10 cm 2 /s. The presence of the second process could be responsible for poor high spatial frequency response of the investigated photopolymer 2 system. Comparison with the diffusion in photopolymer systems known for their good response at high spatial frequencies shows that both investigated diffusion processes measured here occur in a much faster time scale.
A reflection hologram for visual indication of environmental humidity has been studied. The hologram is recorded in a self-developing photopolymer and changes color when exposed to a change in humidity and is fully reversible. The range of color change, reversibility, and the response time of the hologram have been studied in a controlled humidity environment. Fully reversible holograms with response times from few seconds to tens of minutes have been designed. Extremely sensitive bright visual humidity indicators, capable of dramatic color change within a few seconds of breathing on them are demonstrated.
The humidity and temperature responses of a reflection hologram recorded in a selfprocessing photopolymer layer have been characterised by measurement of the position of the maximum intensity in the spectral response of the hologram. It has been demonstrated that such a hologram can be used for indication of the relative humidity (RH) in a specific temperature range. The operational range and reversibility of the holograms have been characterised in a controlled humidity and temperature environment. The humidity studies were carried out in the range from 10 to 80% RH and the temperature range under study was 15 -50 ºC.
Recommended Citation Raghavendra, R. et al. (2008) Raman spectroscopy for the characterization of the polymerization rate in an acrylamide-based photopolymer. Applied Optics, Vol. 47, no. 2, pp. 206-212. doi:10.1364 corresponding to carbon-carbon double bond of methylenebisacrylamide using Raman spectroscopy. To study the dependence of the polymerization rate on intensity and to find the dependence parameter, the polymerization rate constant was measured at different intensities.A comparison with a commercially available photopolymer shows that the polymerization rate in this photopolymer is much faster.
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