Grüneisen data from the free surface velocity of thermoelastic materials

Abstract

A technique is presented for the measurement of the Grüneisen parameter Γ of a solid from the free surface velocity induced by pulsed energy deposition. The technique is applied to both energy -(internal energy density) dependent and energy-independent Grüneisen data. The measurements employ a velocity interferometer to determine the free surface velocity of solids exposed to a pulsed electron beam. For the cases where Γ is independent of temperature, or energy density, the Γ values are obtained from the maximum free surface velocity as a function of incident fluence. Energy-dependent Grüneisen data are extracted by an analysis based on the differentiation of the free surface velocity with respect to the initial energy density of the solid. The analysis takes into account the effects of both the finite exposure time of the electron pulses and the delay time of the interferometer. Results are presented for Al, Cu, Ge, and Si in a temperature range where Γ is constant. In addition, for silicon Γ is measured as a function of energy over the temperature range 50–300°K, where Γ is strongly energy dependent. In all cases the results are in excellent agreement with the thermodynamic values.