In Active Thermography energy is deposited on the sample surface by illuminating it in a controlled way. This excitation results in a local temperature enhancement and a temperature gradient which drives a heat current through the sample. The diffusion of heat is influenced by material properties as well as by the existence of defects inside the sample. Thus from measurements of temperature transients, which can be done either on the same side of the excitation (reflection mode) or on its opposite side (transmission mode), conclusions can be derived with respect to material and defect properties.
