How to Tailor Structural Colors for Extended Visibility and White Light Generation Employing Direct Laser Interference Patterning

The appearance of a surface can be controlled by creating periodic microstructures designed to diffract light and produce structural colors. Nevertheless, since structural coloration is based on diffraction, the produced colors have a strong dependence on the viewing angle and absence of coloration takes place while tilting the samples. In this work direct laser interference patterning is used to firstly provide transparent polymer sheets a structural coloration with a high-range observation angle, and secondly to demonstrate the combination of structural colors, producing a white coloring effect. The employed approaches are based on the fabrication of micro-gratings with multiple periods in the same structured area and on the engineering of the diffraction orders of the diffraction spectrum. The patterned surfaces are characterized by confocal microscopy and angular spectrometry in reflection mode. The morphological characterization shows homogeneous surface patterns, while the spectral results demonstrate that combining four spatial periods on a single patterned surface, a white appearance is obtained over an angular observation range higher than 30 degrees. The experimental results are supported by theoretical predictions by means of generalized formulas based on the diffraction of light.