Tuning structural coloration through evanescent wave absorption at microscale concave interfaces

14 March 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Here, structural color generated by total internal reflection (TIR) interference at microscale concave interfaces is tuned via evanescent wave absorption by dyes. Using quantitative angle-resolved spectral analysis combined with ray tracing simulation, it is demonstrated that the multibounce TIR trajectories enhance the efficiency of dye absorption and usefulness in modulating the reflected colors. Depending on the absorbance spectrum of the dye used, and the amount of dye coated at the TIR interface, the angle-dependent reflected colors can be predictably altered. The use of a near-infrared absorbing dye allows for the combination of overt color-shifting iridescent effects under illumination with visible wavelengths and covert optical-motion effects under near-infrared. This work, which explores an innovative approach for controlling the reflective properties of iridescent structurally colored materials, may be of interest both for fundamental research and for applications such as sensors, coatings, and security.

Keywords

structural color
total internal reflection
evanescent wave
iridescent
microstructure

Supplementary materials

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SI
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Methods, SI figures
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Video S1
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Video S1. A sample of circular patterned microstructures made by greyscale lithography with airbushed IR-813 toluenesulfonate in the center illuminated under visible room lighting to show the iridescence and invisibility of the near-IR absorbing dye. Scale bar is 5 mm.
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Video S2
Description
Video S2. A sample of circular patterned microstructures made by greyscale lithography with airbrushed IR-813 toluenesulfonate in the center illuminated under a near-IR flashlight to show the dimmed reflectance in the center and iridescence in the regions not coated by the dye. Scale bar is 5 mm.
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