Tuning Coloration through Evanescent Wave Absorption at Microscale Concave Interfaces

Reflected coloration can be generated in microtextured materials via multipath total internal reflection interference. Here, the reflected iridescent coloration is tuned through the dye absorption of the evanescent wave that is generated at the optical interface upon total internal reflection. Using quantitative angle-resolved spectral analysis combined with a ray tracing simulation, it is demonstrated that the multibounce total internal reflection trajectories enhance the efficiency of dye absorption and the usefulness in modulating the reflected colors. Depending on the absorbance spectrum of the dye used and the amount of dye coated on the optical 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 wavelengths. This work, which explores an innovative approach for controlling the reflective properties of iridescent, structurally colored materials, has relevance both for fundamental research and for applications such as sensors, coatings, and security.