Characteristic properties of laser ablation of translucent targets

Abstract

This study reveals the characteristic features of the laser ablation of the solid Nd:Y 2 O 3 targets, such as the dynamics of the laser plume, the crater depth, and the weight and size distribution of liquid melt droplets. The ablation was initiated by the ytterbium fiber laser radiation pulses with constant energy (0.67 J) and with different power densities. The dependence on the power density of such parameters as the injection time of drops, mass distribution of drops, crater depth, and productivity of synthesis of nonopowder was revealed. To explain the formation of deep craters a model was proposed, stating that the formation of liquid droplets is a consequence of the Kelvin-Helmholtz instability's appearing and developing on the border between the liquid melt on the crater's wall and the vapor flow from the crater. The increment of this instability and its characteristic size was determined.

From the Laser Plume to the Laser Ceramics

“…If such defects are located inside the target in the area of the laser beam incidence, the initial heating also occurs inside the target (in the area of these defects). Then, due to the strong temperature dependence of the absorption coefficient, a heat wave is formed [33], which moves along the laser beam from the defect to the target surface, upon reaching which a laser plume is formed. This process is compounded by the fact that after repeated exposure, the surface of the initial target is covered with a layer of transparent melt 100-400 μm thick, in which the defect concentration is much lower than in the initial target made of sintered micro-powder.…”

“…When nanopowders are obtained using both lasers, in addition to nanoparticles, spherical particles with sizes from 0.5 to 150 μm are also formed [29,33], as well as shapeless target fragments of the same size. Fragments are formed after the end of radiation exposure to a specific part of the target due to thermal splitting of the cooling fused layer [30].…”

“…A similar pattern is observed in the evaporation of targets from YSZ and FeMgAl 2 O 4 . Theoretical analysis [33] allowed us to establish that one of the reasons for the appearance of drops in the laser flare is related to the presence of melt in the crater and is due to the development of the Kelvin-Helmholtz instability that is formed between the liquid wall of the crater and the flow of expiring vapor. This analysis made it possible to establish the characteristic size of the instability: 100 ,…”