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.
The aim of this paper is to discuss the benefits as well as the limitations of utilizing photopolymer materials in the design of holograms that are responsive to changes in their environment, such as changes in the concentration of a specific substance, temperature, and pressure. Three different case studies are presented, including both surface and volume phase holograms, in order to demonstrate the flexibility in the approach of utilizing holographic photopolymers for the design of sensors and interactive optical devices. First, a functionalized surface relief hologram is demonstrated to operate as an optical sensor for the detection of metal ions in water. The sensitivity and selectivity of the sensor are investigated. The second example demonstrates a volume transmission hologram recorded in a temperature-sensitive photopolymer and the memory effects of its exposure to elevated temperature. Finally, a pressure-sensitive reflection hologram that changes color under application of pressure is characterized, and its potential application in document authentication is described.
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