7 December 1992 OPTOGELs: optically active xerogels
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Using the sol-gel process, we synthesized zirconia/silica matrices doped with different organic dyes (rhodamine 640, ...). These samples were used to perform optical Kerr effect experiments with sequences of ultrashort light pulses (100 fs, 620 nm, 1 (mu) J focused on 50 micrometers diameter) to induce refractive index changes. A permanent birefringence around 7 X 10-5 was obtained. By changing the direction of the polarization of the excitation pulses, we were able to locally control the directions of the neutral axes. We thus demonstrated the possibility of using this media as an all optical memory matrix and such doped xerogels will subsequently be referred to as OPTOGELS. We interpret our results as the possibility of locally controlling the orientation of the doping molecules encaged in the solid host matrix. The memory effect is probably due to links of hydrogen bond type between the organic molecules and the pore surface which prevent thermal reorientation. The electric field of the optical excitation pulses exerts a torque on the molecules. If this torque is greater than the energy linking the molecules to the pore surface, the molecules are temporarily released and aligned in the direction of the pulse polarization. Based on this interpretation, we have developed a model to explain the evolution of the birefringence as a function of the number of excitation pulses.
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Michael Canva, Patrick M. Georges, Alain Brun, Frederic Chaput, Francois Devreux, and Jean-Pierre Boilot "OPTOGELs: optically active xerogels", Proc. SPIE 1758, Sol-Gel Optics II, (7 December 1992); doi: 10.1117/12.132045; https://doi.org/10.1117/12.132045

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