Researchers at the Institute of Electrophysics, Ural Branch, Russian Academy of Sciences in Yekaterinburg have suggested that the industrial ytterbium fiber laser should be used to get functional nanopowers. The work published in the Journal of Applied Physics compared productivity and power inputs when getting nanopowders via fiber and carbon dioxide laser. The work substantiated advantages of the first option. The effort has been accomplished with financial sponsorship of the Presidium of the Russian Academy of Sciences and the Federal Targeted Program “Scientific and Educational Research Staff of Innovative Russia”.
Nanopowders are applied in making structural ceramics, they are used in hydrogen power engineering, many of them are capable of luminescence. Target evaporation with the help of laser radiation is a promising method for obtaining nanopowders.
Utilization of carbon dioxide laser, which was also investigated in their previous efforts by the Yekaterinburg researchers, enables to get particles about 20 nm in dimension. Differences in size, which inevitably occur when getting nanoparticles, are insignificant in case of carbon dioxide laser. However, engineering deficiencies of such laser – capacity instability, low efficiency of conversion of electrical energy into emission, impressive dimensions – are connected with considerable inconveniences, and encourage researchers to seek for new solutions.
A group of researchers guided by Yuri Kotov has suggested that ytterbium fiber lasers should be used in a similar process flow. The experiment involved lasers, produced by the Scientific and Technical Association “IRE-Polus”. They are more efficient than carbon dioxide lasers, however, their wavelength makes 1.07 micrometers (10 times less than that of carbon dioxide laser), and possibility of their utilization to get nanopowders required experimental check.
The target – a material blank for getting substances of required composition - consisted of compressed micron-sized powders of yttrium (Y) and zinc (Zn) oxides. Laser radiation was transmitted via fiber cable to the optical system and was focused on the target. The material blank was equipped by a drive that ensured the target horizontal displacement and rotation for uniform surface processing. The molecules vaporized from the surface were taken away by the inert gas stream and they condensed upon a specially prepared substrate layer.
Under uninterrupted seventeen-hour laser work, the powder output was 390 g – it is approximately three times higher than when using carbon dioxide laser. Additional analysis has confirmed obtaining of practically homogeneous nanopowder, which is close in composition to the target. A set of experiments on getting optical ceramics nanopowders has also proved that ytterbium laser utilization ensures that the final composition of the mixture as compared to the initial composition of the target is distorted to a much less extent than in case of carbon dioxide laser utilization. The researchers primarily connect the above effect with high monochromaticity of the ytterbium laser.
Special attention was paid by the specialists to the search of optimum condition for laser operation. The obtained experimental dependence of productivity on pulse duration upon fixed pulse energy has a typical peak in the range of 100 microseconds. Thus, in the researchers’ opinion, already now “ytterbium fiber lasers should be considered more promising for getting nanopowders, taking into account their higher consumer properties.”