Optothermal interference technique applied to the investigation of transparent layered structures

This papa shows the enhanced sensitivity of the optothermal interference te chnique in the detection of local differences (non-homogeneity in thickness and optothermal parameters), compared to the conventional optical interfer ence, when investigating layered transparent structures. The measured signa l is sensitive to the reflectance variation at the distinct interfaces, fun ction of temperature, as well as to the optical phase lag between the refle cted beams. Measurements made on solar cells show contrast of the order of 100% in the optothermal interference, while the conventional optical interf erence presents a contrast of only 15%. A model based on the reflectance va riation at each interface describes the signal behavior as a function of mo dulation frequency.