Optimization of Recording of Thermal-Wave Images in BDM Method

Abstract

The beam displacement modulation (BDM) method is very difficult to implement and has a lot of features and parameters which require optimization to improve the effectiveness of detection of thermal non-uniformities. The most important parameters that have to be taken under consideration during the optimization process are the width of the excitation source, the displacement speed of the excitation source, and the distance between the excitation and measuring spots. The width of the excitation source (e.g., diameter of laser beam) and speed of beam dislocation, in relation to the surface of the object, influence the spectra of excitation’s energy. It allows examination and visualization of thermal properties of the object at varied depths. This article presents the general scheme of a thermal-wave microscope with the implemented BDM mode and describes the process of optimization for which the assignment is to find the microscope’s settings that guarantee the highest temperature contrast of non-uniformities at the surface of the examined object.