Comparison of structural colors achieved by laser induced periodic surface structures and direct laser interference patterningWednesday (24.06.2020) 13:13 - 13:16 Room 1
Usually, surfaces can be given a predefined coloration by applying a pigment to modify the surface absorbance and reflectance at given wavelengths. Even though this method is widely used, the long term stability of the color quality depends strongly on the pigment sensitivity to external physical and chemical influences, such as UV radiation, interaction with chemicals, mechanical damage or heat. An alternative approach is providing the surface a structural coloration through modification of the surface topography so that it interacts with the incoming light producing optical effects, such as diffraction, interference, or scattering. In this case, the achieved structural color is dependent on the viewing angle, as observed in many natural cases, for example in the multiple sized structure of morpho butterfly wings. The structural coloration stability depends mainly on the mechanical properties of the material. One of the many applications for structural coloration is engraving products with holographic features to prevent piracy and counterfeiting. Laser based methods are commonly used to fabricate these holographic features due to their upscaling potential. Among these, laser induced periodic surface structuring (LIPSS) and two-beams direct laser interference patterning (DLIP) are able to engrave hundreds of grooves with pitch sizes on the micro and sub-micro scale with a single laser pulse, making them attractive for industrial processing. In the case of LIPSS, the resulting grooves form a quasi-periodic array with an effective spatial period close to the used laser wavelength. The LIPSS trenches are aligned perpendicular to the radiation polarization due to the excitation of surface plasmon polaritons. In contrast, DLIP allows the formation of a periodic arrangement of grooves not only on metals but also on ceramics, polymers and glasses, with a well-defined spatial period and with the flexibility to change easily their orientation and spatial period. In this contribution, LIPSS and DLIP methods are used to generate structural colors on metallic surfaces and their structural coloration quality is quantified by using spectroscopic methods as well as imaging optics. Combining the characterization methods, the optimum laser process parameters, such as fluence and pulse-to-pulse overlap, are evaluated. Moreover, the LIPSS and DLIP potential to achieve intense structural colors are quantitatively compared.
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