# Surface Plasmon Polariton Triggered Generation of 1D-Low Spatial Frequency LIPSS on Fused Silica
## 1 Introduction  
Over the last few decades, Laser-Induced Periodic Surface Structures (LIPSS) have gained increasing attention due to the common availability of ultrashort pulsed laser sources. Additionally, intensified research has been raised by their widely diversified potential applications in wettability [1; 2; 3], tribology [4; 5; 6], cell cultivation [7; 8; 9] or anti-reflection coating [10]. These self-assembled structures were firstly reported by [PERSON] in 1965 after irradiation of a semiconductor with a polarized laser [11]. They typically arise on solid materials upon polarized laser irradiation with the fluence being near the materials' ablation threshold [12; 13; 1]. LIPSS have been shown on all material classes such as conductors [1; 2; 14], semiconductors [5; 11; 12] and dielectrics [12; 15; 16]. Please note, due to the availability of free charge carriers, texturing conductors and semiconductors with LIPSS is significantly simpler than structuring dielectrics. Two types of LIPSS are generally distinguished in the literature by the relation between the applied laser wavelength \(\lambda\) and their spatial periodicity \(\Lambda\), namely Low Spatial Frequency LIPSS (LSFL) and High Spatial Frequency LIPSS (HSFL). While LSFL reveal a periodicity close to \(\lambda\), HSFL have a periodicity significantly smaller than \(\lambda\)[12; 15; 17]. The origin of LSFL is described by [PERSON] et al. [18] as the interaction of the electromagnetic field of the laser and a surface scattered wave generated by the incident laser light. This surface scattered wave that forms the basis of the so-called efficacy factor theory was later associated with Surface Plasmon Polaritons (SPP) [19]. The generation of surface plasmon polaritons is used in several publications with respect to a better LIPSS understanding [17; 20; 21; 22; 23]. SPP are formed, e.g., on a metal-dielectric interface with ambientair acting like a dielectric with positive permittivity (\(\epsilon>0\)) and metals having a negative permittivity (\(\epsilon<0\)) [21; 22; 24; 25]. For the generation of LSFL on a dielectric material such as glass in ambient air with positive permittivity, however, the conditions for SPP excitation are not fulfilled. Yet, for these materials, LIPSS can also be generated due to the excitation of free charge carriers in the dielectric material by ultrashort pulsed laser irradiation, turning the dielectric surface into a metallic state [17; 20; 21; 22]. This excitation mechanism is related to multiphoton and avalanche ionization processes [26]. While the majority of scientific studies of LSFL on dielectric materials are based on punctual structures [12; 15; 27; 28], i.e., LSFL are generated on a single spot only, for industrial applications, the generation of one- and two-dimensional LSFL is mandatory by scanning the laser. For metals [1; 2; 3; 4; 14; 29; 30] and semiconductors [5; 31; 32; 33], this has been shown in several publications because of the convenience in generating LSFL on these materials with free charged carriers (\(\epsilon<0\)). For dielectric materials, e.g., fused silica, the authors recently have shown the transfer from punctual laser irradiation into the dynamic range, i.e., moving the laser spot over the sample [16]. However, these so-called one-Dimensional LSFL (1D-LSFL) reveal periodicities larger than the wavelength of the applied laser and an orientation parallel to the polarization of the laser under normal irradiation, and neither conform with the established SPP theory. This supra-wavelength (\(\Lambda_{LSFL}>\lambda\)) type of LIPSS has been reported in several publications for punctual laser irradiation of dielectrics [34; 35; 36] with their generation being attributed to hydrodynamic instabilities within a convection roll-driven formation [34]. Beside these supra-wavelength structures, the common way LSFL are shown on fused silica for punctual irradiation is \(\Lambda_{LSFL}<\lambda\) and still being parallel to the polarization of the laser [12; 15; 28; 36].