Thermal properties measurement using Mirage-Effect experiment

Abstract

The analysis of the heat transport in insulator crystals has always been the focus of research because the knowledge that can be gained on the fundamental physical mechanisms governing the heat transport can help in the development of efficient thermal management strategies for many technological applications. Thermal properties of materials usually give us practical information about its properties. Experimental measurement of thermal properties is the main subject for this thesis. We built a Mirage-Effect experiment to measure thermal properties of materials where its main concept is to focus a modulated heat source on the surface of the sample. As heat is absorbed, it will create a temperature gradient arising in the gas near the surface which will create a gradient of refractive index of the gas. This gradient is detected by another probe laser skimming the surface of the heated spot where the deflection of this probe beam is detected through a four position detector. The main concept of the experiment is based on generating thermal waves on the surfaces of the elaborated samples. These waves are determined by the thermal properties of the samples. Their propagation in the air just above the boundary will create a gradient of refraction index in the air. This will allow the probe laser beam to deflect. The deflection of the probe laser beam as a function of the distance from the heating spot will allow the determination of the thermal properties of sample under consideration. The deflection of the probe beam has two components: transverse and normal. We do a multi-parameter fit of the experimental results with the expression of the deflection where we can deduce the values of thermal diffusivity and thermal conductivity of the material. We also measure the thermal diffusivity and thermal conductivity of a set of silicon carbide samples characterized by different dozes of proton bombardment in order to study the effect of bombardment of protons on the thermal efficiency of SiC.