## 4 Results and Discussions
### The Scattering Microstructure and the Simulation of Its Making
One disadvantage is the greater complexity and lower repeatability of the resulting microstructures. The structural elements formed as a result of processing with a laser influence can be considered as macroelements. In the case described, such structures are Gaussian-shaped craters. The effect of forming LIPSSs and roughness structures with a femtosecond laser on both normal and inclined surfaces is known [12]. Subsequent femtosecond post-processing  
Figure 4: Additional periodic structure (roughness in the form of LIPSS) formed between craters (R), atomic force microscopy: (**a**) the surface height, (**b**) the amplitude error data for more clear mapping of thin structure elements. Figure 3: Optimally modelled surface with a complex two-periodic structure which can be formed by two passes of a femtosecond laser and used for simulation. is presumably capable of forming additional roughness or LIPS microstructures on the surfaces of the mentioned macroelements. Such a complex microstructure inside the crater can be formed due to the distribution of pulse power on the surface, different from the power distribution according to the normal Gaussian distribution, as well as due to complex thermal processes occurring during the formation of the crater, which lead to the formation of chaotic (Figure 5), LIPSSs or so-called coffee rings structures [11]. Also, the formation of such structures can be performed using a femtosecond laser. Moreover, the formation of microstructures can be additionally carried out by targeted post-processing of the surface of previously formed macrostructures. However, this post-processing can lead to damage to the existing macrostructure through its fusion, when forming a microstructure on the surface of macrostructural elements, in the case of low-melting-point materials processing. Therefore, the most important condition for the effective implementation of the processing technology is the defining processing technologies and modes because the wrong treatment regime may lead to high heat flux into the part and cause its melting and deformation [32,33]. Therefore, the formation of such structures can be effectively performed using a femtosecond laser, since femtosecond-scale pulses provide processing at a low overall heat flux. The precision accuracy and absolute repeatability of individual relief elements are not required to achieve better scattering. This allows us to recognize the effect of uncontrolled or partially controlled formation of microstructures as useful in terms of cost and speed of formation of a complex two-period structure on a reflective surface. In the context of the widespread struggle to improve quality and reduce the cost of production processes [34], this is especially important. A fully controlled process of obtaining a two-periodic structure by mutual displacement of the laser emitter and the surface being processed makes it possible to obtain a microstructure with specified characteristics, whereas the error is determined by the equipment characteristics. This process is characterized by the possibility of obtaining the most homogeneous microstructure and high repeatability. Thus, a partially controlled process for obtaining a microstructure is simpler but does not guarantee that the surface will give a scattering pattern in accordance with the calculated one. However, a fully controlled  
Figure 5: Formation of chaotic microstructures at the bottom of craters when laser energy is distributed along the radius of the beam in accordance with the Gaussian normal distribution law. Formed irregularities on the crater floor (**a**). The process of formation of irregularities at the bottom of the crater due to increased heating of the wall of the formed crater (**b**). process is more complex and places greater demands on the equipment used, but the practical result will be as close as possible to the theoretically obtained one.