Characterization Of Wedged Samples Using Laser Induced Photothermal Radiometry

Photothermal radiometry (PTR) technology has been proved to be a powerful tool forcharacterization and nondestructive evaluation (NDE) of thermophysical properties ofvaries materials. It is well known that the photothermal fields are very sensitive to thegeometries of the samples. For different geometries, different theoretical models areneeded. In the past decades, most of the investigations are limited to samples of simple flatstructure. In recent years, PTR investigations are extended to curved samples such ascylindrical and spherical samples. In this paper, we further extended the PTR research towedge-like samples. We established a theoretical model for a wedge-like sampleilluminated by a modulated incident beam by means of the Green function method incylindrical coordinates. An analytical expression for the thermal-wave field in suchsamples is presented. Based on the theoretical model, the characteristics of the thermalwave fields are simulated with different parameters. It is shown that the temperature fieldsshow different behaviors when we change the sample and the experimental parameters,such as the detection point, the open angle of the wedged sample, and the modulationfrequency of incident energy beam. The theory is first theoretically validated by reducingthe arbitrary wedged geometrical structure to the simple ones and comparing the resultswith other theoretical models in literatures in some special cases. Furthermore,experimental validation is also presented with a wedge-like sample. The theory provides asolid theoretical basis to quantitatively characterize the wedge-shaped samples, such assintered wedge samples, using photothermal method in a noncontact and nondestructiveway.