The optical limiting properties of a thin film (~150 microm) of chemically enhanced bacteriorhodopsin under cw laser illumination is investigated. The effective nonlinearity n(2) of the film is measured with the z-scan method. Anomalous absorption at different wavelengths as a function of illumination intensity is observed.
The wavelength-dependent refractive index of a bacteriorhodopsin thin film is measured by the use of a modified critical-angle technique. The effect of the host bovine skin gelatin on the refractive index is analyzed. The measured data on the thin film can be useful for system applications. The methods and procedures are generally applicable to any optically absorbing thin films.
An optically addressed spatial light modulator based on a thin film of chemically enhanced bacteriorhodopsin is demonstrated. Incoherent-to-coherent light conversion is achieved by exploitation of both the large shift in absorption maxima accompanying the bR-M phototransformation and the extended M-intermediate lifetime resulting from the chemical enhancement of the protein at high pH. The device exhibits a linear dynamic range of 120:1 at 514 nm and a resolution of-100 line pairs/mm.
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