Femtosecond laser modification of plasmonic color and diffuse reflectance of semicontinuous aluminum film-insulator-metal mirror structures

Plasmonic nanostructures can efficiently absorb and scatter light, and thus exhibit vibrant colors. Colors originate from the excitation of plasmon resonances – collective oscillations of free electrons in metallic nanoparticles. Semicontinuous metal films (SMF) are a special type of disordered plasmonic structures that can be mass-produced in a rather inexpensive physical vapor deposition process. SMFs are comprised of random in their nature nano-island structures of various sizes and shapes resonating at different wavelengths. When irradiated with high-intensity laser radiation, the nanostructures can be locally modified. Spatially local restructuring originates from highly localized SMF absorption of light in hotspots, regions of a high local electric field. Thus, the optical response of the film can be altered in a spectrally selective manner. Hence, locally different colors are obtained. In this work, we demonstrate the generation of structural plasmonic colors through femtosecond laser-induced modification of thin semicontinuous aluminum films deposited on an aluminum mirror coated with an isolator layer. The structures show vivid colors in reflection. The effects of laser parameters on final color are explored. In addition, we report laser-induced control of diffuse reflectance of aluminum SMF structures. Self-passivation effect of aluminum results in the long-term stability of generated colors.