Thermal diffusivity is a thermophysical property that quantifies the ratio of the rate at which heat is conducted through a material to the amount of energy stored in a material. The pulsed laser diffusion (PLD) method is a widely used technique for measuring thermal diffusivities of materials. This technique is based on the fact that the diffusivity of a sample may be inferred from measurement of the time-dependent temperature profile at a point on the surface of a sample that has been exposed to a pulse of radiant energy from a laser or flash lamp. The standard approach to PLD is based on a simple model that produces an explicit relationship between the diffusivity and the time required for the temperature of the sample surface to reach a specified fraction of the peak temperature. However, the standard approach is based on idealizations that are difficult to achieve in practice, so models that represent a PLD measurement system with greater fidelity are desired.
Assessment of the impact of the approximations made in the development of the standard approach showed that neglect of the spatial and temporal variations of the input power leads to significant errors in measurement of the thermal diffusivity. The objective of this paper is to present the Distributed Source Finite Absorption model which represents the spatial and temporal variations in the pulse with greater fidelity.
The cost of the increased fidelity is an increase in the complexity of the algorithm used to determine values of the thermal diffusivity. A simple relationship between an easily determined characteristic of the measured temperature profile and the thermal diffusivity does not exist. Therefore, a new method of extracting values from measured time dependent-temperature profiles based on a genetic algorithm and on reduced order modeling has been developed. This paper also presents a numerical verification of this proposed new method for measuring the thermal diffusivity.