## 3 Results  
It was found that at the threshold laser intensity of 33 kW/cm\({}^{2}\) the HP-HT nanodiamond film surface can start blackening in the laser beam waist area both in ambient and Ar atmospheres. When the film and the focused beam move relative to each other at a low speed (about 0.1 mm/s), blackening light start in some areas of the film. During irradiation of spots on the stationary film blackening typically does not occur. In other words, there are areas where neither green emission generation nor blackening occurs under the laser radiation of even higher than 33 kW/cm\({}^{2}\) (up to 65 kW/cm\({}^{2}\)) intensity. These areas are clearly visible in Figure 1b as white regions. Therefore, it is much easier to get the film blackened moving it relative to the laser beam (i.e. producing a line) than irradiating the motionless film at a single point. Numerous experiments have shown that a stationary film can also be blackened, depending on the region of the film. However, the probability of finding such a region is quite low. The use of 10\(\times\) and 50\(\times\) objectives, which provided maximum power densities of 3 and 20 kW/cm\({}^{2}\), respectively, did not lead to blackening, as the power densities were lower than the threshold of laser blackening (33 kW/cm\({}^{2}\)). It should also be noted that blackening did not occur on the film with a thickness of 0.5 \(\upmu\)m at maximum intensity, whether it was moving or stationary. One can see a line, a square, and a triangle \"written\" on the surface of the 20 \(\upmu\)m thick film in Figure 6. The optical images in Figure 6 were obtained while using a microscope and a camera incorporated into a Raman spectrometer. It can be seen that the width of the blackened segments in the transverse direction is about 5 \(\upmu\)m, which is slightly larger than the diameter of the laser beam waist (4.1 \(\upmu\)m). The blackening of the film was shown to be accompanied by green emission by visual observation through a glass filter of the laser irradiated area (Figure 5a). One can see the red spot of the reflected laser in that area when \(P\) = 5.4 kW/cm\({}^{2}\) and blackening of the film does not occur, and green emission at \(P\) = 65 kW/cm\({}^{2}\)m accompanied by the film blackening in Figure 5c,d. Note that that the observed green emission is a one-time event for the irradiated area, i.e. no emission is observed after blackening the film area. Figure 7a shows the optical transmittance of the blackened region of the film at a wavelength of 633 nm, depending on its coordinate along the \(x\)-axis perpendicular to the \(y\)-axis, which is parallel to the symmetry axis of the blackened line (see Figure 7d). The presented dependence was obtained using a photodetector, the photosensitive part of which with the diameter of 1 cm was placed in the immediate vicinity of the film while the film and the focused beam move relative to each other (100\(\times\)). The transmittance of the film is shown to be significantly decreased after laser exposure. Figure 7b shows the Raman spectra that were obtained for non-blackened and blackened regions of the film at an intensity of 5.4 kW/cm\({}^{2}\) using a 100\(\times\) objective. One can see a strong Raman signal with a frequency shift of 1331 cm\({}^{-1}\), slightly different from that of a bulk crystalline diamond [32], in the spectrum of a non-blackened region (Figure 7b, black curve). Note that, depending on the wavelength of the pumping laser and the nanoparticle mean size, the Raman shifts of detonation nanodiamonds, CVD nanodiamonds, and HP-HT nanodiamonds are known to be in the range of 1325-1332 cm\({}^{-1}\)[33; 34; 35; 36; 37; 38]. In the Raman spectrum of a blackened region, there is no diamond signal (see Figure 7b, red curve), but  
Figure 6: Laser written patterns on the HP-HT nanodiamond film surface: (**a**) line, (**b**) square, and (**c**) triangle under white light illumination.