Tailoring Multibounce Reflection Interference with Microscale Refractive Interfaces

Developing approaches to tailor iridescence generated by microscale structures is essential for applications ranging from sensors to security materials. Here, we achieve tunable iridescence by combining microscale refractory interfaces with concave microstructures to generate multibounce reflection interference. By incorporating designed refractory interfaces, we demonstrate the ability to control the distribution of illumination angles entering the structured cavity thereby modulating the resulting color and reflection efficiency. Experimental analysis of Janus droplets combined with ray tracing simulations highlight how refractory elements modify the optical paths of multibounce reflections and alter the angle-dependent coloration. Additionally, we investigate the incorporation of axion lenses that refract and focus light onto the microstructure to increase reflection efficiency while maintaining color saturation. The integration of refractory interfaces with reflective microstructure cavities provides customizable routes to tailor the structural coloration and reflection performance of multibounce reflection interference, advancing the design of high-performance optical materials.