Holographic storage in sensitized polymethyl methacrylate blocks

The storage properties of thick PMMA-blocks, sensitized for =514 nm and containing residual monomer, are investigated by making use of holographic methods. The fundamental refractive index grating amplitude shows a characteristic development in a two-beam holographic experiment. A remarkable self-development of the light induced refractive index change is observed just as considerable higher harmonic amplitudes (strong nonlinear response). The recording-sensitivity is small in comparison to that of other storage materials and adversely affected by appreciable holographic scattering. The behavior of the samples during long storage times is investigated and the possibility of thermal fixing and superposition of holograms is shown. The interpretation of the observed properties and the behavior in the holographic experiments suggests a model of the microscopic processes: storage is essentially performed by light induced polymerisation of residual monomer.