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

Area of Science:

• Materials Science and Engineering
• Optics and Photonics
• Nanotechnology

Background:

• Increasing demand for structural coloration techniques that produce both base color and iridescent sheen on transparent substrates.
• Need for efficient, single-step fabrication methods for periodic and localized modulation of thin-film structures.

Purpose of the Study:

• To design, deposit, and process a composite thin-film structure for tunable structural coloration.
• To achieve precise control over thermal accumulation and surface morphology using burst-mode femtosecond laser processing.
• To create transparent structural colors with iridescent sheen effects on soda-lime glass substrates.

Main Methods:

• Fabrication of an aluminum nitride-aluminum (AlN-Al) thin film on a soda-lime glass substrate.
• Processing using burst-mode femtosecond laser, varying sub-pulse number, pulse-to-pulse distance, and average power.
• Characterization using reflectance spectra, transmittance data, microscopy (confocal, SEM), energy-dispersive spectrometry, and finite-difference time-domain (FDTD) simulations.

Main Results:

• Systematic variation of laser parameters achieved precise control over thermal accumulation and surface protrusion morphology.
• Observed color variation attributed to laser-induced air gaps between Al and AlN layers, not compositional changes.
• Periodic surface protrusion structures were identified as the governing factor for the iridescent sheen effect.

Conclusions:

• The burst-mode femtosecond laser processing enables large-scale patterning of structural colors with high transmittance.
• The method produces coupled interference- and diffraction-based structural colors with angle-independent base color and angle-dependent iridescent sheen.
• Promising applications in decorative elements, anti-counterfeiting, and encryption requiring combined visual effects.