Efficiency of fractal structure formation during laser evaporation

The formation of fractals during laser evaporation of various media (metals and dielectrics) by 10-ms Nd laser pulses is studied experimentally as a function of the laser radiation power density and external pressure. It is established that fractals are formed during the action of a laser pulse in the bulk of a plasma plume. It is found that finely dispersed phase forms under a certain critical pressure a bound shell (macrofractal) in peripheral layers of the plume. The presence of the shell confining the plasma expansion leads to a threshold variation of the characteristics of the optical discharge.