The Laser Flash Analysis (LFA) has established itself as a reliable method for determining the thermal diffusivity of materials [1]. In order to extend the measurement range of LFA, the investigation of temperature evolution on the side facing the laser pulse, referred to as the front side, is the focus of this research. This problem is addressed, by applying an adiabatic front side model in a first investigation step [2]. This model provides a fundamental approximation of the temperature profile on the front side of the sample.
To cope with the high dynamics of the front side temperature caused by the pulsed energy input of the laser, a modification of the evaluation models is necessary [3]. In this regard, the temporal development of the front side temperature in the adiabatic state is convolved with laser pulses of different shapes. This convolution allows for a detailed investigation of the effects of various laser pulse shapes and pulse times on the temperature profile on the front side. This analysis considers not only the maximum temperature but also the temporal evolution of the temperature. The investigation of laser pulse shape proves to be a critical aspect, as it significantly influences the response signal of the front side.
Two different convolution methods are compared using numerical solutions. One involves convolution by multiplication in the Fourier domain using Fast Fourier Transformation followed by inverse transformation, while the other is the analytical solution through the convolution integral. Both results are thoroughly compared with numerically simulated front side data from a laser flash measurement on a graphite sample, testing their robustness and applicability (see figure 1 and 2).
To further validate the precision and applicability of the developed analytical model, the temperature data measured on the front side of a graphite sample is fitted with the newly created model. The fitting result for thermal diffusivity is compared with the result obtained for thermal diffusivity using a standard evaluation method from the simultaneously measured temperature development on the back side of the graphite sample, assessing the suitability of the analytical models.