The laser flash analysis or laser flash method is used to measure thermal diffusivity of a variety of different materials. An energy pulse heats one side of a plane-parallel sample and the resulting time dependent temperature rise on the backside due to the energy input is detected. The higher the thermal diffusivity of the sample, the faster the energy reaches the backside. A laser flash apparatus (LFA) to measure thermal diffusivity over a broad temperature range, is shown on the right hand side.
In a one-dimensional, adiabatic case the thermal diffusivity is calculated from this temperature rise as follows:
Where
As the coefficient 0.1388 is dimensionless, the formula works also for and in their corresponding SI units.