The storage of volume holographic reflection gratings in low-toxicity photopolymers represents a challenge at present since they can be used in many important applications such as biosensors and holographic optical elements. In this context, an acrylate-based photopolymer developed in our research group was employed to study the recording of unslanted holographic reflection gratings at high spatial frequencies. The optimal preparation conditions of the photopolymer layers were determinated. The diffraction efficiencies are measured in both recording and curing stage and a comparative study of these values was realized. In addition, a theoretical study using Kogelnik’s coupled wave theory was carried out with the aim of understanding the diffraction efficiency behaviour of both processes. In this work, a maximum diffraction efficiency of 14.1% was reached after a curing process in 150 µm layers at a recording wavelength of 488 nm. This value represents a good result compared to that reported in the literature and opens the way to reflection mode holography research using low-toxicity material.
Holographic gratings stored in low-toxicity photopolymer, Biophotopol, have been analyzed to achieve stable and efficient holograms. A curing process allows the hologram stabilization, but at the same time, it could produce a diffraction efficiency (DE) reduction. Here, a detailed low-cost LED curing protocol is shown to stabilize over time 1205 l/mm transmission holograms, and at the same time, a 33% DE increment (with respect non-curing holograms) have been demonstrated. Finally, to obtain a better understanding of DE change, a theoretical fit of our experimental result, based on Kogelnik's coupled wave theory was carried out and discussed.
The recording of volume holographic reflection gratings in eco-friendly photopolymers represents a challenge at present since they can be used in many important applications such as holographic optical elements and biosensors. In this sense, the aim of this work has been fabricated reflection gratings in the symmetrical experimental in "Biophotopol" and to study the dependence of diffraction efficiency on physical thickness, recording intensity and exposure energy. An increase in diffraction efficiency was observed when the photopolymer films were cured with a LED lamp to improve the stability of the reflection holograms. The maximums diffraction efficiencies around 30 % were obtained for reflection gratings with a spatial frequency of 4888 lines/mm. The index modulation and optical thickness were obtained by fitting procedure through Kogelnik's coupled wave theory. Experimental and theoretical results have been interpreted to modify the photopolymer formulation and exposure conditions in order to increase the diffraction efficiencies.
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