In the global market, the exterior appearance of products plays a big role. Companies put a lot of attention and effort for decorating their products in order to distinguish them from other competitors. The most common technologies that are used to control the aesthetical appearance of surfaces are based on inks, like inkjet printing, pad printing or screen-printing. Alternatively, laser surface processing methods can also provide specific surface modifications that can be of advantage in decorative applications.
In this work, we present the four-beam Direct Laser Interference Patterning(DLIP) technology for enabling colorful surface decoration without any ink. This technology is based on the ablation of the irradiated material using an interference pattern. The conventional laser marking process utilizes a single focused Gaussian laser beam to ablate directly the material. Thus, the marked motives can be of high resolution (spot size – few tens of µm) but always consist of only a single color (e.g. black, white or grey) depending on structured material and process parameters. In contrast, the four-beam DLIP exploits the interference of four symmetrically distributed beams to produce the periodical intensity pattern within the focused Gaussian spot. This leads to a 2D diffraction grating formation in each single pixel. The decorative motive consisting of such pixels with gratings disperse the incident white light into its components (rainbow color) resulting in colorful appearance. The exclusive ability of this technology to change the grating period on the fly during the processing gives the possibility to mark images with various diffractive colors.
As testing material, a standard stainless steel was selected. The treated surfaces are analyzed with confocal and scanning electron microscopy. The effect of the laser processing parameters on the diffraction efficiency are analyzed using optical spectrometry. Also, the different processing strategies capable to transform the digital image to the real colorful motive on the material are described. Finally, various motives fabricated with four-beam DLIP and consisting of various colors are demonstrated.