## 4 Discussion
The best effect was achieved by sanding the sample with 800-grit sandpaper using a manual two-disc grinder and polisher--Saphir 330, ATM GmbH (Blieskastel, Germany), a German product--and then etching with a mixture of concentrated (65%) hydrochloric and nitric acid in a volume ratio of 3:1, and subsequently darkening the sample surface with graphite or alcohol-based black ink from a common permanent marker. The sample prepared in this way was subject to much less deformation during the laser texturing process. With appropriately selected laser parameters, the problem of deformation was almost completely eliminated. Darkening the surface also prevented spark formation. The visual difference between the remelting effect of the prepared and untreated surfaces can be observed in Figure 8, where only the upper part of the sample was ground, etched, and blackened, while the lower part remained unchanged. The figure shows how the final effect of applying the laser beam on the surface layer of the sample changes during a single sequence without changing the other parameters. The remelting process for this sample started from the lower left corner and ended in the upper right corner. Laser parameters were set as follows: power 2500 W, frequency 3 Hz, and focus 1.5 mm. Microscopic observation confirmed that the surface preparation makes a crucial difference in dimple formation. Figure 9 shows pictures of the raw AISI 316L surface subjected to laser texturing, while Figure 10 presents magnifications of the ground, etched, and darken  
Figure 8: Comparison of the texturing effect of the etched and blackened surface (upper part of the sample) and the unpretreated surface (lower part of the sample). The unpretreated steel surface subjected to laser beam modifications developed stretched, overlapping dimples with funnel-like shapes of material ejected during the ablation. Funnel-like, shaped dimple edges all followed the blowing direction of the shielding gas. It could be assumed that the stainless steel was melted, pushed out of the melt zone created by the laser beam, and moved by a steady blast of blown argon. The specific shape of dimple edges must have an impact on many physical properties, especially heat exchange and liquid flow parameters which could formulate another interesting research topic for further study. However, since the shape is mostly irregular and not repeatable, this phenomena cannot be taken into consideration as a modification technique. Also, strong pattern damage caused by sparkle formation can be observed, especially in Figure 9a,b. Some local burns can be observed at the bottom of each dimple. On the other end of the sample, dimples created on the pre-treated surface look much more regular. The obtained pattern should be possible to recreate. No burns or sparkles were observed during the texturing process. Setting the focus parameter to 1.5 mm resulted in obtaining a dimple diameter of 1.48 mm. Dimples overlap evenly. Similar shapes of the dimples were obtained by [PERSON] et al. [10], who also used Nd:YAG laser and compared its effectiveness in titanium texturing to a CO\({}_{2}\) laser. Scientists concluded that the processing assisted by the Nd:YAG laser was more suitable to modify the surface layer of titanium samples. They also found out that less splashes and more regular features were obtained using Nd:YAG rather than a CO\({}_{2}\) laser. However, the researchers emphasized that more research and further studies were needed. Samples prepared this way could be taken into consideration for further study. More analysis and measurements, including surface roughness tests, will be performed in the future. Since it was already discovered and described in many literature positions,  
Figure 10: Etched and blackened AISI 316L surface subjected to laser texturing of 2500 W laser beam power with pulse focus of 0.5 mm and frequency of 3 Hz: (**a**) 10\(\times\) magnification by ZEISS; (**b**) 50\(\times\) magnification by Olympus; and (**c**) 100\(\times\) magnification by Olympus.