Abstract :
Phase transition on the surface of an aluminium target and vapour plasma induced by laser irradiation in the nanosecond regime at the
wavelengths of 1.06 and 0.248 mm with an intensity of 108–109 W/cm2 in vacuum are analysed. Particular attention is paid to the wavelength
dependence of the observed phenomena and the non-one-dimensional effect caused by the Gaussian laser intensity distribution. A transient twodimensional
model is used which includes conductive heat transfer in the condensed phase, radiative gas dynamics and laser radiation transfer in
the plasma as well as surface evaporation and back condensation at the phase interface. It is shown that distinctions in phase transition dynamics for
the 1.06 and 0.248 mm radiation result from essentially different characteristics of the laser-induced plasmas. For the 1.06 mm radiation,
evaporation stops after the formation of hot optically thick plasma, can occasionally resume at a later stage of the pulse, proceeds non-uniformly in
the spot area, and the major contribution to the mass removal occurs in the outer part of the irradiated region. Plasma induced by the 0.248 mm laser
is much more transparent therefore evaporation does not stop but continues in the subsonic regime with the Mach number of about 0.1.
