Fig. 3: Comparison of reflection behavior of flat cholesteric films and densely packed CSRs on black background. | Light: Science & Applications

Fig. 3: Comparison of reflection behavior of flat cholesteric films and densely packed CSRs on black background.

From: Unclonable human-invisible machine vision markers leveraging the omnidirectional chiral Bragg diffraction of cholesteric spherical reflectors

Fig. 3

Three flat films of polymerized cholesteric liquid crystal (a) with vertical helix, with red, green and blue retroreflection color, respectively, are compared to three samples with close-packed CSRs (b) in cured NOA160 glue, with near-IR, green and blue retroreflection, respectively. The red and green films and the near-IR CSRs have right-handed helix while the blue film and the green and blue CSRs have left-handed helix. Three white-light illumination and full-color imaging configurations are compared, as illustrated in the schematics on the left; top: diffuse outdoor illumination around noon on a cloudy day; middle: collimated light along a direction mirroring the imaging direction, the mirror plane containing the sample normal; bottom: collimated light parallel to the imaging direction. For each configuration, five imaging angles α are compared, without polarizer and through right- and left-handed circular polarizer, respectively

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