Highly Transparent Structural Colors with Iridescent Sheen via Burst-Mode Laser Processing

The growing demand for structural coloration methods that simultaneously exhibit an iridescent sheen effect and a base color on transparent substrates calls for a single-step fabrication procedure capable of periodic and localized modulation of thin-film structure. In this work, a composite thin-film structure consisting of aluminum nitride-aluminum (AlN-Al)-soda-lime glass substrate is designed, deposited, and subsequently processed using burst-mode femtosecond laser. By systematically varying the number of sub-pulses, the pulse-to-pulse distance, and the average laser power while maintaining a fixed single-sub-pulse energy (1 μJ), the precise control over thermal accumulation and surface protrusion morphology is achieved, resulting in a series of highly transparent structural colors with iridescent sheen effects. Reflectance spectra, transmittance data, confocal microscopy, scanning electron microscopy and coupled energy dispersive spectrometer analyses, and the finite-difference time-domain simulations reveal that the observed color variation originates from laser-induced air gaps between the Al and AlN layers, rather than from compositional changes, and that the resulting periodic surface protrusion structures govern the iridescent sheen effect. The proposed method enables large-scale patterning while preserving high transmittance, as demonstrated by the desired hue, saturation, and iridescent sheen. This burst-mode laser processing strategy offers a material- and production line-compatible route for realizing coupled interference- and diffraction-based structural colors, with promising applications in decorative purposes with anti-counterfeiting or encryption purposes, where both angle-independent base color and angle-dependent iridescent sheen effect are required.