20 December 2004 Chiral and nanostructured optical materials
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Porous thin films of TiO2 exhibit interesting and useful optical properties when the glancing angle deposition (GLAD) technique is used to impart controlled structural variations on the nanometer scale. Specifically, helically structured thin films possess optical properties sensitive to the polarization state of incoming light, including selective reflection of circular polarizations and optical rotation of the vibration ellipse of light as it passes through the film. By adjusting the deposition parameters, the helical structures can be transformed into vertically aligned columns with nanometer diameter variations. These films possess a continuously varying refractive index along the substrate normal. This index profile can be tailored so that it varies sinusoidally along the substrate normal to form a rugate interference filter. With the addition of a constant index layer of thickness equal to the sine period located in the center of the film, a narrow bandpass appears within the filter’s larger reflectance band.
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Matthew M. Hawkeye, Andy C. van Popta, Jeremy C. Sit, Michael J. Brett, "Chiral and nanostructured optical materials", Proc. SPIE 5577, Photonics North 2004: Optical Components and Devices, (20 December 2004); doi: 10.1117/12.567559; https://doi.org/10.1117/12.567559

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