Abstract:The patterning of an acrylamide-based photopolymer surface by holographic recording is studied. The patterns are induced by light alone and no post-processing is required. Periodic surface modulation is observed in addition to a volume phase grating. An investigation has been carried out using white light interferometry into the dependence of the amplitude of the photoinduced surface relief modulation on the spatial frequency, intensity of recording and sample thickness. The observed dependencies indicate that the diffusion of material during the holographic recording plays a major role in surface relief formation. The possibility for inscription of surface relief patterns opens the door to at least two new applications for this photopolymer: fabrication of diffractive optical elements and biosensors.
A novel composition for a low-toxicity, water-soluble, holographic photopolymer capable of recording bright reflection gratings with diffraction efficiency of up to 50% is reported. The unique combination of two chemical components, namely, a chain transfer agent and a free radical scavenger, is reported to enhance the holographic recording ability of a diacetone acrylamide (DA)-based photopolymer in reflection mode by 3-fold. Characterization of the dependence of diffraction efficiency of the reflection gratings on spatial frequency, recording intensity, exposure energy, and recording wavelength has been carried out for the new low-toxicity material. The use of UV postexposure as a method of improving the stability of the photopolymer-based reflection holograms is reported. The ability of the modified DA photopolymer to record bright Denisyuk holograms which are viewable in different lighting conditions is demonstrated.
There is an increasing need for environmentally friendly holographic recording materials which can be produced in bulk with little risk to the health of workers in manufacturing. This is why the development of non-toxic photopolymer materials is crucial, and has attracted attention in recent years. Composition and preliminary characterization of a new non-toxic photopolymer material are presented. It operates well at a range of spatial frequencies, and achieves diffraction efficiencies and refractive index modulation comparable to the known acrylamide-based photopolymers.
The composition of the low toxicity, environmentally-compatible Diacetone Acrylamide photopolymer has been modified with the inclusion of different additives. The addition of glycerol to the photopolymer composition is described. Results show that the incorporation of glycerol results in a uniform maximum refractive index modulation for recording intensities in the range of 1-20mW/cm 2 . This may be attributed to glycerol's nature as a plasticizer, which allows for faster diffusion of un-reacted monomer within the grating during holographic recording. An optimum recording intensity of 0.5mW/cm 2 is observed for exposure energies of 20-60mW/cm 2 . The modified photopolymer achieves a refractive index modulation of 2.2x10 -3 , with diffraction efficiencies up to 90% in 100µm layers. Glycerol has also shown to reduce the rate of photobleaching of the diacetone acrylamide photopolymer. This is possibly due to more prevalent inhibition effects caused by increased oxygenation of the photopolymer layers. The stability of the photopolymer samples is also improved with the addition of glycerol.
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