Free-Jet Expansions from Laser-Vaporized Planar Surfaces

Abstract

Characteristics of free-jet vapor expansions created by the pulsed-laser vaporization of some refractory materials are examined. Such expansions were generated from planar surfaces at laser power densities up to 2.5 MW/sq cm. Time-integrated and time-resolved photography were used to show that the structure and pressures of such flows are correlated by the same relationship that is valid for free jets from orifice flows. Data show that the vapor velocity becomes sonic at or very near the vaporizing surface. A method is presented for deriving vaporization pressure from flow-field photos; such pressures from carbon-vaporization data for temperatures to 4500 K are in good agreement with extrapolated equilibrium vapor pressures. It is shown that this technique may be a means to determine vapor pressures of refractory materials at high temperatures.