Selective glass surface modification with picosecond laser pulses for spatially resolved gloss reduction

Today, gloss and other properties describing the reflectance of a surface are important in a wide range of applications, e.g., for displays of mobile phones and laptops. Influencing the visual appearance and therewith the quality of an object, an inadequate gloss can lead to rejection of an item. Hence, these properties have to be precisely adapted to each application. Specifically, gloss reduction of spatially limited areas is quite challenging using common techniques such as chemical etching: Etch masks are required to prohibit the modification of the surrounding surface. This is sophisticated, expensive, and comparatively inflexible. Unlike with mask based processes, laser micromachining results in a very flexible tool for the modification of optical properties of selected surface areas. Furthermore, by using ultrashort laser pulses, the surface structuring is precise; it causes minimal thermal damage outside the micromachined area and shows a maximum degree of flexibility in terms of the geometry of the fabricated structures. Our approach aims for the selective adjustment of the specular gloss level of glass surfaces by applying picosecond laser pulses at a wavelength of 1064 nm. The size and the morphology, as well as the density and the order of the structures, have been tailored in our work. Besides, a detailed investigation of the structures generated by picosecond pulses by means of an optical microscope and atomic force microscope (AFM) is presented. Based on the findings of the AFM-measurements, simplified surface structures were modeled using SolidWorks and the corresponding laser beam reflection was simulated using Zemax. Finally, a numerical model of the specular gloss of laser modified surfaces was implemented, and it was compared with the experimental results. As a result, the novel method of laser based gloss reduction provided a defined adjustment of the specular gloss between 30 and 150 GU. This paper will discuss not only advantages but also specific limitations concerning the laser based method.