Time dependences of the effective diameter (a) and concentration of particles of the condensed-phase of zinc (b) at its laser erosion under the action of a submicrosecond pulse. d , μ m; N , cm − 3 ; t , μ sec. 

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... the fine-disperse liquid drop phase of the target material. After 450 nsec from the beginning of irradiation the transmission of the erosion torch increases, which is explained by the decrease in the number of particles and the increase in their sizes. To determine the numerical concentration of condensed-phase particles and their sizes, we created an experimental facility. This facility differs from the one shown in Fig. 1 in that instead of a semiconductor laser, a free-run- ning ruby laser lasing at a wavelength of 0.7 μ m during 1000 μ sec is used. This permits probing the erosion laser torch during a much longer time interval than with the use of a semiconductor laser. The time resolution therewith is determined by the spike structure of the ruby laser oscillation and is equal to 5–10 μ sec. Another important differ- ence of the given experimental facility is that the laser target is placed in an integrating sphere. This permits simulta- neous control of the incident (probing) radiation intensity of the ruby laser transmitted through the erosion torch and of the probing radiation scattered by it to all sides. The absorbed part of the ruby laser probing radiation is calculated from the energy balance. From the ratio of the absorbed and scattered components of the probing radiation one can control in real time the sizes of particles, as well as their numerical concentration. These methods are described in more detail in [12]. Figure 3 shows the time dependence of the coefficient of transmission by the erosion laser zinc torch of the ruby laser probing radiation. Probing is carried out at a height of 1 mm from the target surface. The acting radiation parameters are the same as in Fig. 2. As is seen from Fig. 3, the erosion torch transmissivity increases in the course of time up to 180 μ sec (from the moment of action), after which the probing radiation losses are insignificant. This points to the fact that in the course of time the number of particles of the liquid-drop phase decreases and their sizes increase. Results and Discussion. With the use of the laser probing methods [12], the time dependences of sizes (effective parameters) of particles (Fig. 4a) and their numerical concentration (Fig. 4b) have been obtained. These dependences are in good agreement with the shape of the curves shown in Figs. 2 and 3. As is seen from Fig. 4, the particle sizes are much smaller than those given in [11] and in the course of time they increase, which points to condensation as a probable mechanism of their formation. In so doing, the numerical concentration of particles markedly decreases, which also confirms the presence of condensation processes. Thus, from the experiments performed it follows that from a certain instant of time after the onset of irradiation of the zinc target by submicrosecond laser radiation an erosion laser torch with intensive luminescence of destruction products is formed. As the acting radiation decays, the luminescence intensity of the torch decreases with some time delay from the acting pulse and small liquid-drop particles of the target material condense from the torch vapors. In the course of time their sizes increase and the concentration decreases, which makes it possible to speak of condensation as the most probable mechanism of their formation. Erosion laser torch transmittivity measurements by both the semiconductor and ruby lasers also point qualitatively to the proceeding of condensation processes in the torch. Conclusions. The results of the investigations performed show that the use of submicrosecond laser pulses is promising for obtaining nanoparticles of metals. The application of modern frequency lasers for generating short pulses makes it possible to develop technologies of forming media containing nanoparticles of ...