  We study methods for calculating the thermal diffusivity of solids from laser
flash experiments. This experiment involves subjecting the front surface of a
small sample of the material to a heat pulse and recording the resulting
temperature rise on the opposite (rear) surface. Recently, a method was
developed for calculating the thermal diffusivity from the rear-surface
temperature rise, which was shown to produce improved estimates compared with
the commonly used half-time approach. This so-called rear-surface integral
method produced a formula for calculating the thermal diffusivity of
homogeneous samples under the assumption that the heat pulse is instantaneously
absorbed uniformly into a thin layer at the front surface. In this paper, we
show how the rear-surface integral method can be applied to a more physically
realistic heat flow model involving the actual heat pulse shape from the laser
flash experiment. New thermal diffusivity formulas are derived for handling
arbitrary pulse shapes for either a homogeneous sample or a heterogeneous
sample comprising two layers of different materials. Presented numerical
experiments confirm the accuracy of the new formulas and demonstrate how they
can be applied to the kinds of experimental data arising from the laser flash
experiment.
