Laser‐induced bursts of subsurface superheated liquid Mo

Abstract

Laser‐induced subsurface superheating of molybdenum causes an inrush and ejection of liquid molybdenum at the surface. The inhomogeneous, intermittent turbulent pattern is frozen by ultrafast cooling when the laser pulse is switched off. Corresponding Reynolds numbers are estimated to span the range from 11 000 to 90 000, similar to the R_e number for ‘turbulence in a boundary layer’. The similarity with the morphology of supersonic jets indicates that the velocity of ejected liquid molybdenum is close to Mach 6. The eddies of the turbulent pattern follow a lognormal distribution. Analysis of the two‐dimensional turbulent pattern from a fractal aspect was performed on the basis of an iterated function system of the ‘dragon’ type. Most of the real turbulent formations were obtained as union sets by contraction mapping (contraction factor S = 0.66) of the basic hyperbolic set C (the dragon image). Fractal dimensions (capacity D, information δ, and correlation coefficient v) were found to be in the range 1.53–1.68, giving, for the universal constant μ, the range of values 0.6–0.9, characteristic of irregular cascading. To our knowledge this is the first observation of this kind.