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.