Dynamics of Thermal Emission Attendant to Tungsten Vapor Condensation in Gaseous and Superfluid Helium

A tungsten target has been exposed to pulsed laser ablation in vacuum, gaseous helium, and superfluid (liquid) helium, and ablation products have been studied by means of pyrometric measurements. It has been shown that quantitative measurement data for thermal emission characteristics shed light on nanostructure condensation mechanisms in these media. From these data, the cross sections of emitting particles have been calculated. It has been found that submicrometer particles emit mostly in vacuum, whereas emission from nanoparticles has been observed in superfluid helium. The obtained data are substantiated by electron microscopic data.