## 4 Results and Discussions  
### The Scattering Microstructure and the Simulation of Its Making  
Computer modeling of the process of surface microstructure formation was performed in the COMSOL Multiphysics(r) version 6.2 environment. Surface shaping, in this study, was carried out due to the temperature effect of the laser beam on the material being processed; \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Material**} & **Average** & **Speed,** & **Pulse Duration,** & **Repetition** & **Step,** \\  & **Power, [W]** & **[m/s]** & **[fs]** & **Rate, [kHz]** & **[\(\upmu\)m]** \\ \hline SET 1 & 0.5 & 0.7 & 266 & 500 & 20 \\ SET 2 & 0.5 & 0.9 & 266 & 500 & 20 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Laser parameters. Figure 1: Formation of a two-period structure: Formation of a single crater in the case of energy distribution along the radius of the beam in accordance with the Gaussian normal distribution law (**a–c**). Formation of a series of craters at equal distances, in one pass, along the coordinate of the processing direction (**a–f**). Formation of a series of craters at equal distance l1 during the second pass of the laser beam along the line of processing, with a craters shift of distance l2 relative to the initial coordinate of the first pass’s first crater (**g–k**). The resulting two-periodic structure (**m**). which are formed by successive laser pulses. We have practically obtained a surface with this microrelief. The formation of such a structure is quite well managed. The same distance can be achieved (Figure 1f pos. \(l_{1}\); Figure 2 pos. \(l_{1}\)) by uniform mutual displacement of the laser emitter and the object being processed along the coordinate of the processing direction. The following figures (Figure 2 pos. S and Figure 3 pos. S) show the envelope S of the projection of the section of the plane (A-A) directed perpendicular to the surface of the sample and along the line of formed craters after the first processing. The designation 1 in the figure Figure 2 pos. \(l_{1}\) represent the same distance as in the (Figure 1f pos. \(l_{1}\)). A two-periodic structure can be obtained by mutual displacement of the laser emitter and the object being processed along the coordinate of the processing direction after completion of the pass at a given offset distance (Figure 3 pos. \(l_{2}\)). In this case, the subsequent pass forms an additional similar mono-periodic structure (Figure 1g). This structure, superimposed on the relief obtained after the first pass along the coordinate of the processing direction, forms a complex two-periodic surface microstructure (Figure 1, position (m)). A two-periodic structure can also be created by alternately (\(l1\to l2\to l1\to l2\to...\)) changing the value of the mutual displacement after each subsequent pulse. The following figures (Figure 3 pos. S) show the section (A-A) along the processing path after two passes with mutual starting displacement (Figure 1i pos \(l_{2}\); Figure 3 pos \(l_{2}\)). At present, this microrelief has practically not been obtained, and is being studied theoretically for its reflective and scattering properties, using computer models. Figure 2: Surfaces with a complex mono-periodic structure, formed by a femtosecond laser while saving the LIPSS of the base surface (**a**) by using laser parameters of SET 1; (**b**) by using laser parameters of SET 2, which are shown in Table 1.  
Also, the process of obtaining a complex periodic structure can be partially controlled. In this case, the complex scattering structure consists of equidistant craters with a complexly structured surface of the walls and bottom, different from the smooth Gaussian shape (Figure 4 pos. R). Structures obtained by the two-wave mixing method can be considered as an example of a partially controlled process to form a complex periodic structure [31]. The advantages of this method are undoubtedly in terms of the technology and speed of the surface structuring.