## 2 Experimental Setup  
Mechanical treated surfaces of gas-dynamic seals and reference samples made of silicon carbide-based ceramic material were irradiated in a pulsed-periodic mode. The diameter of these gas-dynamic seals of the compressor rotor of a gas-turbine engine was 90 mm. An ultraviolet laser LCS-DTL-374 QT (Laser-export. Co. Ltd., Moscow, Russia) with the wavelength of 355 nm was used. The maximum average power was 90 mW, while the pulse energy was 50 \(\upmu\)J, with a duration of a single pulse of less than 10 ns. The laser was incorporated into the CLWS-200 circular laser writing station [41; 42], which included movable mechanics and an optical control system consisting of a 40\(\times\) magnification microlens, rotating mirrors, an aperture, and an additional lens. The computer systems integrated in the control station ensured the samples movement in the angular direction with a resolution of about 0.25 angular seconds and the optical head movement in the radial direction with a resolution of approximately 0.6 nanometers.  
The CLWS-200 circular laser writing station (Institute of Automation and Electrometry SB RAS, Novosibirsk, Russia) was mounted on a granite table equipped with an anti-vibration system that was installed on a metal base. This protection system was intended to diminish the influence of vibrations on the precision characteristics of the components of the system. The granite base plate was equipped with a slot in which the rotation drive spindle group was located. This group had three supports for adjusting its horizontal position. A motor rotated the spindle that represented a gas-lubricated aerostatic bearing. The control system of the recording head was designated for ensuring the specified size of the laser spot on the specimen surface during the treatment process. The main task of the system was to maintain a constant distance between the objective lens (equivalent lens) and the sample plane and to ensure a specified (zero) offset at the defocusing sensor. Figure 1 illustrates a scheme and Figure 2 presents a photo of the laser writing station with an UV nanosecond laser.  
The results of exposure of the focused UV laser beam on the ceramic material were verified using a Zygo NewView 7300 (Zygo Corporation, Middlefield, OH, USA) optical profilometer. The universal three-dimensional surface structure analyzer provided a graphical representation and a high-resolution numerical analysis for accurate determination of the surface structure of the tested parts using MetroPro software. This device used scanning white light interferometry to display and perform non-contact measurements of the microstructure and to determine the surface topography by means of visible-wavelength light in three dimensions.  
The tribological properties of the obtained structures were investigated using the TRB-SE tribometer (CSM Instruments, Peseux, Switzerland), shown in Figure 3. The tribometer can measure a friction force of up to 10 N according to ASTM G99 standard. The LVDT sensor resolution was 0.02 \(\upmu\)m. To measure the necessary parameters of the sample, a \"ball-on-disk\" test scheme was used. This scheme implied pressing the ball against a flat surface. The sample surfaces were examined by a scanning electron microscope (SEM), Supra-25 (Carl Zeiss, Jena, Germany).  
Figure 1: Schematic representation of the CLWS-200 laser writing station.  
Figure 2: Photo of the CLWS-200 laser writing station with an LCS-DTL-374 QT ultraviolet laser.