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Based on a literature review, it was concluded that Laser-induced Periodic Surface Structures (LIPSS) on polymers are produced when applying laser sources operating either in the ultraviolet wavelength and nanosecond pulse duration, or radiation of wavelengths ranging from 265nm to 1045nm and pulse durations in the femtosecond regime. LIPSS were not reported when using picosecond laser sources. The purpose of this paper is to study whether (and if so which) LIPSS form on polymers when picosecond pulsed laser source is applied. Low Spatial Frequency LIPSS (LSFL) and High Spatial Frequency LIPSS (HSFL) have been obtained on polycarbonate and on polystyrene when applying picosecond laser pulses at a wavelength of 343nm on single spots and on processed lines. When using a wavelength of 515nm, LSFL and HSFL have been produced only on polycarbonate, but also led to porosity of the structured area.
DOI: 10.2961/jlmn.2018.02.0010
Keywords: laser-induced periodic surface structures (LIPSS); low spatial frequency LIPSS (LSFL); high spatial frequency LIPSS (LSFL); Polycarbonate (PC); Polystyrene (PS); picosecond laser source
1. Introduction
Laser induced Periodic Surface Structures (LIPSS) are regular nanoscale structures which develop on top of surfaces when processed with a linear or circular polarized laser beam in a narrow range of fluence levels close to the ablation threshold [1]. LIPSS have been observed on a wide range of materials, such as metals [2-5], semiconductors [2,6-10], dielectrics [2,11-13], ceramics [14] and polymers [15-22]. LIPSS were found first on semiconductors by Birnbaum [6] in 1965. His discovery led to an extensive research on this universal phenomenon [23]. LIPSS come in a wide range of shapes, e.g. ripples [23], pillars [24], grooves and cones [25]. Most researched LIPSS are low spatial frequency LIPSS (LSFL) which are ripples with a distinct orientation, either parallel or perpendicular to the laser polarization (depending on the material) and a spatial periodicity Л close to the laser wavelength 1 [23]. In the early 2000s, when commercial ultra-short pulsed laser sources entered the market, LIPSS with a periodicity Л much smaller than the laser wavelength 1 have been observed (Л<<1). These LIPSS are referred to as High spatial frequency LIPSS (HSFL) [23]. The properties of these structures (the spatial period and amplitude) are controlled by several laser parameters including the laser wavelength, the type of...