Holographic thin films, spatial light modulators, and optical associative memories based on bacteriorhodopsin

The diffraction efficiency and nonlinear transmission properties of chemically enhanced thin films of bacteriorhodopsin are analyzed by using absorption spectroscopy, the Kramers-Kronig transformation, coupled wave theory, and a simplified kinetic model of the bacteriorhodopsin photocycle. Photoconversion of bR to a 50:50 mixture of bR and M generates a large change in refractive index that is proportional to the bacteriorhodopsin concentration and is greatest in regions where the difference in absorption coefficients is smallest. The predicted diffraction efficiencies are dominated by large phase components in regions of minimal bR and M absorption. The maximum diffraction efficiency (11) for a 2.5 OD, 150 micrometers thick film occurs at readout wavelengths between 620 nm - 700 nm. These films also exhibit significant nonlinearity in transmissivity at low laser intensities and could find potential use in spatial filtering applications. A real time optical associative memory based on holographic thin films of bacteriorhodopsin is also discussed.

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