Modeling the photochemical effects present during holographic grating formation in photopolymer materials

Abstract

The development of a theoretical model of the processes present during the formation of a holographic grating in photopolymer materials is crucial in enabling further development of holographic applications. To achieve this, it is necessary to understand the photochemical and photophysical processes involved and to isolate their effects, enabling each to be modeled accurately. While photopolymer materials are practical materials for use as holographic recording media, understanding the recording mechanisms will allow their limitations for certain processes to be overcome. In this paper we report generalizations of the nonlocal polymer driven diffusion ͑NPDD͒ model to include the effects of photosensitive dye absorption and the inhibition effects.

Extended model of the photoinitiation mechanisms in photopolymer materials

“…Since the primary radicals are generated in pairs, [2][3][4][5][6][7][8]16 the rate equation governing ͓ED͔ can be presented in the same fashion,…”

“…͑b͒ The second reaction involves the free radical undergoing dye bleaching. [1][2][3][4][5][6][7]15,17 This occurs when the dye radical, see Eq. ͑4͒, abstracts the proton which the ED radical cation released at an earlier stage, see Eq.…”

“…The excited singlet state can return to its ground state by radiationless energy transfer to another molecule such as triethanolamine, which acts as an electron donor ͑ED͒, and by the emission of a photon by fluorescence. 1,2,[4][5][6][7]12 We assume that these processes take place at an overall rate of recovery, r 1 . The resulting singlet state dye can also undergo intersystem crossing into the more stable and longer-lived triplet state, 1 …”

“…͑a͒ The first is the initiation of the polymerization process in the presence of monomer, [1][2][3][4][5][6][7] ED…”

“…[1][2][3][4] The resulting models attempt to take account of the effects of ͑i͒ the photon absorption, ͑ii͒ the regeneration or recovery of absorptive photosensitizer, and ͑iii͒ photosensitizer bleaching. In this paper, the photoinitiation mechanisms involved during holographic recording in a polyvinyl alcohol/acrylamide ͑PVA/AA͒ based photopolymer [5][6][7][8][9][10][11] is studied. The aim is to precisely predict the number of photons that are absorbed by the photosensitizer, which result in the generation of primary radicals, ED · ͑or R · ͒.…”