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Holographic recording of 2D photonic crystals in photosensitized PMMA

Volume phase holography is used for the recording of refractive index patterns with the symmetry of a photonic crystal. As a recording material solid plates of PMMA, containing up to 10 wt% of residual monomer MMA doped with the photo-initiators either Titanocendichloride or DMPA have been used. In both cases the mechanism for the formation of the desired refractive index pattern is the photo-induced residual polymerisation. The recording of the more-dimensional patterns has been performed via 2 different ways. First a consecutive method was applied: While the first pattern is developing the sample is turned by an arbitrary angle and a second volume phase grating with a different lattice-constant was recorded. For the second single-step method we used a 3-beam holographic set-up. Simulations showed different 2-dimensional light-intensity patterns depending on the orientation and the polarisation of the wave-vectors of the 3 interfering beams. Using the photo-induced residual polymerisation we were able to transfer these light-patterns into refractive-index patterns. After recording the sample is developed and fixed by a thermal treatment. The obtained 2-dimensional crystals are characterised using a goniometer with 2 rotary stages by the evaluation of the diffraction patterns. The different diffracted orders may be indexed according to their (h,k) Miller's indices. For the single-step method we were able to verify experimentally the simulated photonic structures.