Tuning structural coloration through evanescent wave absorption at microscale concave interfaces

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.