1：Experimental Design and Method Selection:

The study uses ultrashort laser pulses to induce periodic surface patterns on metallic surfaces, acting as diffraction gratings to generate structural colours. The influence of defects in the ripples structure on the colourising effects is investigated.

2：Sample Selection and Data Sources:

Stainless steel surfaces are used as samples. The surface topology is studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM).

3：List of Experimental Equipment and Materials:

Diode-pumped Yb:KYW thin-disc femtosecond laser (JenLas D2.fs, Jenoptik), scanning electron microscopy (SEM, Zeiss EVO MA 15), atomic force microscopy (AFM, Nanoscope 5, Bruker Corp.), white light source SCHOTT KL 1500 electronic, spectrometer (Ocean Optics, USB2000+), photo camera (Panasonic, DMC-G70KA Lumix G).

4：fs, Jenoptik), scanning electron microscopy (SEM, Zeiss EVO MA 15), atomic force microscopy (AFM, Nanoscope 5, Bruker Corp.), white light source SCHOTT KL 1500 electronic, spectrometer (Ocean Optics, USB2000+), photo camera (Panasonic, DMC-G70KA Lumix G). Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: Laser processing is performed to create ripples on the stainless steel surface. The optical properties of the LIPSS covering the samples are analysed using a setup that enables observation of the structural colours revealed after illuminating the surface with white light.

5：Data Analysis Methods:

The periodicity of the patterns is analysed by means of two-dimensional fast Fourier transformation (2D-FFT). The optical properties are quantified by optical spectroscopy.