Synthesis of Fe:MgAl$_2$O$_4$ nanopowders into laser plum

The features of production of Fe:MgAl$_2$O$_4$ nanopowders by evaporation of targets made from a simple oxide mixture (Fe$_2$O$_3$, MgO, Al$_2$O$_3$) by repetitively pulsed CO$_2$ laser radiation with I=1.6 MW/cm$^2$ peak power density and P$_{aver}$=600 W average radiation power as well as by ytterbium fiber laser radiation (I=0.4 MW/cm$^2$ and P$_{aver}$=300 W) were studied. It was demonstrated that the nanopowder produced with the use of the CO$_2$ laser has the specific surface of 56 m$^2$/g and contains two crystalline phases, i.e. MgAl$_2$O$_4$ (98.2 wt%) and MgO (1.8 wt%) with Fe ions dissolved in them. At the average radiation power of 600 W the output of the nanopowder was 16 g/h. For the nanopowder produced using the ytterbium fiber laser twofold increase of the specific surface (105 m$^2$/g) was observed. This nanopowder contains four phases, i.e. MgAl$_2$O$_4$ (67.5 wt%), $\gamma$-Al$_2$O$_3$ (24.8 wt%), Fe$_3$O$_4$ (3.2 wt%) and MgO (4.5 wt%). In this case the output of the nanopowder was 2.7 g/h due to formation of a “forest-like” array of 4$\div$5 mm high spikes covered with a semitransparent melt layer. Significant differences in the phase compositions of the nanopowders obtained using these lasers are associated with a higher rate of the laser plume cooling for the ytterbium fiber laser.