Topography Tuning for Plasmonic Color Enhancement via Picosecond Laser Bursts

The tuning of 3D topographical features on silver for the production of plasmonic colors is reported. The topography is produced by applying closely time-spaced laser bursts. Using laser bursts increases the Chroma of the colors produced by up to 100% compared to the nonburst coloring method. By adjusting the energy distribution of the laser pulses in a burst, while maintaining the total burst energy constant, significantly different color palettes and topographical structures are produced. Scanning electron microscope analysis of the surfaces produced reveals the creation of three distinct sets of laser-induced periodic-like surface structures (LIPSS): low spatial frequency LIPSS (LSFL), high spatial frequency LIPSS (HSFL), and large LIPSS that have a period about 7x that of the laser wavelength. Two-temperature model simulations of silver irradiated by a laser burst show a significant increase in the electron-phonon coupling which is mainly responsible for the creation of LIPSS. Finite-difference time-domain simulations of a model of the surface, consisting of nanoparticles arranged on a sinusoidal-modulated surface of varying amplitude (0 to 150 nm) and period (200 and 1000 nm), elucidate the importance of the HSFL and LSFL structures for color formation, including the increase in Chroma (saturation) observed experimentally.