## 3 Results
there are two distinct broad Raman lines with frequency shifts of maximums of 1320 and 1580 cm\({}^{-1}\), typical for sp\({}^{2}\)-carbon. Figure 7c shows the dependence of Raman peak intensity of the HP-HT nanodiamond on \(x\) coordinate. The HP-HT nanodiamond Raman peak intensity is mirror-symmetric about \(x=0\) in the first approximation. Figure 8a shows a three-dimensional (3D) image of a blackened line segment obtained while using the atomic force microscope. It can be seen that the blackened area is a notch, on both sides of which, there are parallel formations in the form of a ridge, raised above the average level of the film surface. The depth of the notch and the height of the shaft are about 150 and 100 nm, respectively (see Figure 8b). Figure 8: (**a**) Three-dimensional (3D) image of a blackened line segment obtained using AFM; and, (**b**) the blackened line section profile. Figure 7: (**a**) Dependence of differential optical transmittance of the HP-HT nanodiamond film on \(x\) coordinate; (**b**) The Raman spectra of the HP-HT nanodiamond film points located on the \(x\)-axis perpendicular to the laser- blackened line on the film parallel to the \(y\)-axis, with \(x=25\) (black) and \(0\) (red) \(\upmu\)m; (**c**) the dependence of Raman peak intensity of the HP-HT nanodiamond on \(x\) coordinate; and, (**d**) an optical image of a blackened line perpendicular to the \(x\) axis. Figure 9a shows an image of a blackened line segment obtained while using a scanning electron microscope in the mode of secondary electrons detection. The notch located along the line of laser exposure is clearly visible. Its width in the transverse direction is 3.2 \(\upmu\)m, which roughly coincides with the width of the notch presented in the AFM image (see Figure 8). In addition, it can be seen that the zone of laser irradiation extends in the form of two parallel dark stripes with unmodified surface relief along the notch on both its sides. As a result, the width of the laser irradiation zone along the axis perpendicular to the direction of movement of the focused laser beam reaches 18-20 \(\upmu\)m, which is significantly larger than the laser beam waist diameter. Figure 9b shows the SEM image of the area that is located at the bottom of the laser-induced notch shown in Figure 9a. It can be seen that the granularity of the film surface is noticeably reduced after laser modification. The experiments have shown that blackening and green emission are unlikely to occur when the film is stationary. In addition to visual observation, this is confirmed by Raman spectra of the same point on a fixed film. Figure 10a shows the Raman spectra of the film recorded at a randomly chosen area, which was irradiated for intervals of time \(\Delta t\) = 0.5, 10 and 120 min. by 65 kW/cm\({}^{2}\) laser radiation. The spectra were measured after \(\Delta t\) irradiation time at 65 kW/cm\({}^{2}\). It can be seen that the presented spectra have a broad luminescence band in the spectral range of 650-700 nm and one sharp diamond peak with a frequency shift of about 1331 cm\({}^{-1}\). Figure 10b depicts HP-HT nanodiamond Raman peak intensity and its shift in a randomly chosen area of the stationary film as a function of laser exposure time at 65 kW/cm\({}^{2}\). Figure 10c shows fitted HP-HT nanodiamond Raman peaks for the film point irradiated for \(\Delta t\) = 0.5 and 120 min. Figure 10b,c demonstrate that an increase in the duration of laser irradiation \(\Delta t\) does not lead to a noticeable change in the Raman intensity and shift of the HP-HT nanodiamond peak. At the same time, the decrease in the luminescence intensity in a wide spectral range is clearly observed, i.e. the longer the film is irradiated, the lower the luminescence intensity at wavelengths in the spectral range of 650-700 nm (see Figure 10d). It should be emphasized that, during the lengthy experiment, the results of which are shown in Figure 10a, laser-induced blackening of the film did not occur and the green emission was not observed.