Principle of the LFA Method
The laser or light flash method dates back to studies by Parker et al. in 1961.
In carrying out a measurement, the lower surface of a plane parallel sample (see fig. 1) is first heated by a short energy pulse. The resulting temperature change on the upper surface of the sample is then measured with an infrared detector. The typical course of the signals is presented in figure 2 (red curve). The higher the sample’s thermal diffusivity, the steeper the signal increase.
a: Thermal diffusivity
ρ: Density
cp: Specific heat capacity
λ: Thermal conductivity
T: Temperature
Using the half time (t1/2, time value at half signal height) and sample thickness (d), the thermal diffusivity (a) and finally the thermal conductivity (λ) can be calculated by means of the formula in figure 2. Furthermore, the specific heat (cp) of solids can be determined using the signal height (ΔTmax) compared to the signal height of a reference material.
LFA investigations generally take much less time than thermal conductivity measurements by means of GHP (Guarded Hot Plate) or HFM (Heat Flow Meter).
