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.

is calculated from this temperature rise as follows: Where As the coefficient 0.1388 is dimensionless, the formula works also for

[1] In a vertical setup, a light source (e.g. laser, flashlamp) heats the sample from the bottom side and a detector on top detects the time-dependent temperature rise.

[3] Blumm and Opfermann improved the Cape-Lehman-Model with high order solutions of radial transient heat transfer and facial heat loss, non-linear regression routine in case of high heat losses and an advanced, patented pulse length correction.