Laser flash analysis

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 ${\displaystyle a}$ is calculated from this temperature rise as follows:

${\displaystyle a=0.1388\cdot {\frac {d^{2}}{t_{1/2}}}}$

Where

• ${\displaystyle a}$ is the thermal diffusivity in cm²/s
• ${\displaystyle d}$ is the thickness of the sample in cm
• ${\displaystyle t_{1/2}}$ is the time to the half maximum in s

As the coefficient 0.1388 is dimensionless, the formula works also for ${\displaystyle a}$ and ${\displaystyle d}$ in their corresponding SI units.