Volume Hologram Recording with Photopolymerization System

Dependence of the Rate of Photopolymerization on Holographic Properties

Abstract

The holographic properties of photopolymerizable composition sensitive to visible laser were investigated in relation with the rate of photopolymerization. The photopolymerizable layer consists of four components: multifunctional acrylate monomer, methacrylate monomer, organic peroxide (3, 3', 4, 4'-tetra (t-butylperoxycarbonyl) benzophenone) and sensitizing dye (3, 3'-carbonyl bis [7-(diethylamino) coumarin]). Photopolymerization profile was measured by IR spectroscopy for photopolymer film exposed to the 488nm light. The rate of photopolymerization was controlled by changing the irradiation intensity of 488nm light. Diffraction efficiency of the hologram recorded by the photopolymer was decreased with increasing thelaser intensity. The diffraction efficiency was also decreased with increasing the rate of photopolymerization. The increase of the rate of photopolymerization brings about a dense polymer network structure, accompanying an increase of the glass transition temperature. Therefore, the diffusion of monomers from the relatively unexposed areas into the exposed areas was limited. Consequently, the sample will retain a small modulation in index of refraction.