# IR Pulsed Laser Ablation of Carbon Materials in High Vacuum
## 3 Results
Similar values can be calculated from the other CCD images, from which the plasma temperature may range between about 30 eV (for graphite) and 58 eV (in the case of the active carbon target). For a first approximation, the volume of the ellipsoidal plasma can be calculated by its shape. For example, in the case of graphite ablation in vacuum, reported in Figure 5b, the ellipsoidal shape has a volume of about V\({}_{g}\) = 4.8 cm\({}^{3}\), useful to calculate the plasma atom density at 1 \(\upmu\)s from the laser shot, as will be carried out in the following. The CCD images also provide a first approximation of the angular distribution of the carbon atoms emitted in a vacuum, indicating that it is a reduced and more forward-directive emission in the case of graphite and active carbon targets, in which the measured angular aperture is about \(\pm\)40\({}^{\circ}\). The largest angular distribution was found for the glassy carbon ablated target, estimated at \(\pm\)80\({}^{\circ}\). The angular distribution obtained by irradiating HOPG and charcoal is also high, of the order of \(\pm\)70\({}^{\circ}\), while that due to the irradiation of pencil graphite, which is less dense than graphite, is intermediate, of the order of \(\pm\)60\({}^{\circ}\). A better and more accurate angular distribution of emitted ions can be given by ion collector (IC) measurements at different angles concerning the normal to the target direction. For this, the laser normally impinges on the target surface, and the IC is moved angularly from about 0\({}^{\circ}\) up to about 60\({}^{\circ}\). The IC-TOF spectrum shows an ion peak decreasing in intensity and an increase in TOF with the angle increment from the normal direction. Thus, the ion emission decreases with the angle, both as yield and as kinetic energy, according to the literature [32]. Figure 6 shows the IC-TOF spectra in the case of graphite laser ablation at an incidence angle of 45\({}^{\circ}\) and at four different detection angles concerning the normal direction: 0\({}^{\circ}\) (a), 22\({}^{\circ}\) (b), 45\({}^{\circ}\) (c), and 60\({}^{\circ}\) (d), respectively. Figure 5: CCD image of the carbon plasma produced in 1 \(\upmu\)s from the laser ablation of HOPG (**a**), graphite (**b**), pencil graphite (**c**), glassy carbon (**d**), active carbon (**e**), and vegetal graphite (**f**). Such spectra are rich in information; in fact, they indicate and quantify that the angular emission, in terms of total ion yield (peak area), decreases with the detection angle and that the maximum ion energy (the initial part of the ion peak) decreases with the detection angle. Moreover, a photopeak yield dependence on the angle of emission is also measurable, as reported in each spectrum. This last generally decreases with angular detection, but at low angles, its absorption in the densely produced plasma decreases its detected intensity. The peak tail gives information on the less energetic ion components, which generally decreases with the detection angle. Figure 7 shows the plots of the experimental measurements for graphite ablation relative to the carbon ion yield emission (a), maximum ion energy (b), and photopeak yield (c) versus the angle emission concerning the normal to the target surface. Measurements have an error of the order of 6%. The ion yield decreasing with the angle gives information on the close angular distribution of emitted species; the ion energy decreasing with the angle indicates the ion acceleration along the normal direction to the target surface; the photopeak trend, showing a constancy within about 20\({}^{\circ}\) and 50\({}^{\circ}\), indicates that it is strongly absorbed by the dense plasma along the normal direction to the target surface and decreases at large angles of emission; the angular emission of the ions is larger for low-density vegetable carbon and narrower for high-density graphite.